Horticulture - Higher Intellect · Horticulture Gail M. Lang, Ph.d. Series Editor William G....

Horticulture

Ethnobotany

Forestry

Horticulture

Photosynthesis and Respiration

Plant Biotechnology

Plant Cells and Tissues

Plant Development

Plant Diversity

Plant Ecology

Plant Genetics

Plant Nutrition

Horticulture

Gail M. Lang, Ph.d.

Series EditorWilliam G. Hopkins

Professor Emeritus of Biologyuniversity of Western ontario

Horticulture

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Dedicated to my husband Jonathan, and to our parents Ron, Jane, and Annie who nurtured a love for things green and growing

1 10,000 Years of Horticulture 2

2 Classification of Plants 16

3 Propagation and Breeding 30

4 Cultural Requirements 46

5 Ecology and Pest Management 62

6 Commercial Horticulture 78

7 Garden Design 90

8 Horticultural Professions 102

Glossary 108

Bibliography 115 FurtherReading 118 Index 120

vii

“Have you thanked a green plant today?” reads a popular bumper sticker.Indeed,weshouldthankgreenplantsforprovidingthefoodweeat,fiberfortheclothingwewear,woodforbuildingourhouses,andtheoxygenwebreathe.Withoutplants,humansandotheranimalssimplycouldnotexist.Psycholo-giststellusthatplantsalsoprovideasenseofwell-beingandpeaceofmind,whichiswhywepreserveforestedparksinourcities,surroundourhomeswithgardens,andinstallplantsandflowersinourhomesandworkplaces.Giftsofflowersarethemostpopularwaytoacknowledgeweddings,funerals,andothereventsofpassage. Gardeningisoneofthefastest-growinghobbiesinNorthAmericaandtheproductionofornamentalplantscontributesbillionsofdollarsannuallytotheeconomy.

Humanhistoryhasbeenstronglyinfluencedbyplants.Theriseofagri-cultureintheFertileCrescentofMesopotamiabroughtpreviouslyscatteredhunter-gathererstogetherintovillages.Eversince,theavailabilityoflandandwaterforcultivatingplantshasbeenamajorfactorindeterminingthelocationofhumansettlements.Worldexplorationanddiscoverywasdrivenbythesearchforherbsandspices.ThecultivationofNewWorldcrops—sugar,

By William G. Hopkins

viii

cotton,andtobacco—wasresponsiblefortheintroductionofslaverytoAmerica,thehumanandsocialconsequencesofwhicharestillwithus.ThepushwestwardbyEnglishcolonistsintotherichlandsoftheOhioRivervalleyinthemid-1700swasdrivenbytheneedtoincreasecornproductionandwasafactorinprecipitatingtheFrenchandIndianWar.TheIrishpotatofaminein1847setinmotionawaveofmigration,mostlytoNorthAmerica,thatwouldreducethepopulationofIrelandbyhalfoverthenext50years.

As a young university instructor directing biology tutorials in aclassroomthatlookedoutoverawoodedarea,Iwouldaskeachgroupofstudentstolookoutthewindowandtellmewhattheysaw.Moreoftenthannot,thequestionwouldbemetwithablank,questioninglook.Plantsaresomuchapartofourenvironmentandthefabricofoureverydaylivesthattheyrarelyregisterinourconsciousthought.Yet today, facedwithdisappearingrain forests,explodingpopulationgrowth,urbansprawl,andconcernsaboutclimatechange,theproduc-tivecapacityofglobalagriculturalandforestryecosystemsisputunderincreasingpressure.Understandingplantsisevenmoreessentialasweattempttobuildasustainableenvironmentforthefuture.

The GreenWorld series opens doors to the world of plants. Theseriesdescribeswhatplantsare,whatplantsdo,andwhereplantsfitintheoverallschemeofthings.Horticultureshowsushowhumanshavelearnedtocultivateplantsforuseasornamentalsandtoproducefruitsandvegetables.Wealsolearntheimpactofhorticulturalmethodsontheenvironmentandtheimportanceofdevelopingsustainablemeth-odsforfuturefoodproductionandprotectionoftheenvironment.

IntroductIon

2

10,000YearsofHorticulture

Agriculture is not the result of a happening, an idea, an invention, discovery or instruction by a god or goddess.

It is the result of long periods of intimate co-evolution between plants and man.

-- Jack Harlan (1917–1998)American geneticist and plant breeder

The practice of horticulturehas been around for thousands of years,buthowis itrelevanttolife inthetwenty-firstcentury?Plantsstillrepresentanimportantsourceoffood,fuel,clothing,shelter,medicine,perfume,andrecreation;theyalsoaddoxygentotheatmosphereandhelpintheremovaloftoxicwastefromthesoil.Wehavebecomedependentoncommercialhorticulturetosupplyourproduceandotherplantproducts.Whatifyourfavoritefruitsorvegetableswerenolongercommerciallyavail-able?Youwouldeitherhavetocultivatetheplantsyourselforgowithoutthem.Theactofcultivationcouldbeassimpleastheuseofahoetoweedandloosenthegroundunderaberrybushyoufoundinthewoodsorascomplicatedasthedesignandmainte-nanceofayear-roundvegetablegarden.

Horticultureisthescientifictermfortheactofgardening.Itfirstcameintousearoundtheeighteenthcentury,thoughgar-deningitselfhasbeenpracticedformanythousandsofyears.Agardenermustprepareandmaintainthesoil,selectplantsbasedontheclimateandpurposeforthegarden,protectplantsfromadverse weather conditions and pests, and encourage growthwith water and nutrients when necessary. Other roles of thegardenermayincludethepropagation andbreeding of newplants.Allofthesetopicswillbedescribedingreaterdetailthroughoutthisbook.

Forestry,agronomy,andhorticulturemakeupthreebranchesofagriculturalscience.Forestry isadisciplinethatconcentratesontreesthatgrowinaforest.Agronomyfocuseson cerealcrops,suchasoats,barley, andwheatplus the forage crops that feeddomesticatedanimalsinpastures.ThewordhorticulturederivesfromtheLatinwordhortus,whichwasusedinRomantimestodefineagardenonanestate—usuallyonesmallerthanfiveacres.Anythinglargerthanthiswasreferredtoasafarm.

Horticulturecanbedividedintofourareasofspecialty,twoofwhicharededicatedtotheproductionoffood. Thebranchofhorticulturethatspecializesinthegrowthofvegetablecropsis

4

10,000YearsofHorticulture

510,000 Years of Horticulture

calledolericulture,whereaspomologyisdevotedtotheartoffruitcultivation.Vegetablesandsmallfruitssuchasstrawberriesaregrown ingardensbutmayalsobegrown in largecommercialfields.Fruitsfoundontrees,suchasapples,pears,andpeaches,arecultivatedinorchards,whereascitrusandolivetreesaregrowningroves.Grapesareproducedinvineyardsinaprocesscalled

viticulture (Figure1.1).Cultivationofornamentalhouseplantsandfloweringplants

isthethirdbranchofhorticultureandiscalledfloriculture whenconductedonacommercialscale.Thefourthbranch,landscape

horticulture, focuses on woody ornamentals (shrubs and trees),whicharecultivated innurseries fordistributiontothepublic,aswellasturfgrassesusedforlawns.Plantsgrowninorchards,

Figure 1.1 A man inspects grapes in a Burgundy vineyard near Beaune, France. Viticulturalists, scientists who study the cultivation of grapes, plan and oversee the growing of grapes that are used to make wine.

6 Horticulture

vineyards,groves,gardens,greenhouses,andnurseriesallbelongintherealmofhorticulture.

ORIGINSOFHORTICULTURETheoriginsof horticulture arevaguebecausethefirstactsofplantcultivationbyhumanspredatehistoricalrecords.Archaeological dataindicatethatthecultivationofplantsonalargeanddetectablescalecoincidedwithglobalclimatechangesapproximately10,000yearsago.Thewarmer,wetterweatherthatfollowedtheendofthelasticeage causedchangesinsealevel,increasededibleplantdiversity,andcausedhumanmigrationsintonewareas.Thislarge-scalecultiva-tioneventisreferredtoastheneolithic revolution.

Cultivationofplantsonasmallscalemayhavebeenpracticedformany thousandsofyearsprior to this.Theprotectionandencouragementofthegrowthofwildfoodplantsthroughweed-ing,pruning,irrigation,andpestcontrol,alongwiththesimplepropagationofseedsorcuttings,mostlikelyconstitutedsomeofthefirsthumanhorticulture.Theuseoffiretoremovedeadveg-etationandpromotethenewgrowthofdesirableplantsisanotherexampleofhowancienthumansengagedinplantcultivation.

Archaeological evidence suggests that cereal crops weredomesticated first. Domesticated crops have genetic and mor-

phological differencesfromtheirwildancestorsthatmakethembettersuitedforhumanuse.Thesedifferencesweretheresultofnaturalmutationsforcharacteristicssuchasalargergrainsizeinwheat,whichwasselectedforovertimebecausetheearlyhorti-culturistsplantedonlythelargerseedsthatcontainedthegeneticsequencesforthesetraits.Mostofthedomesticated,edible plantswecultivatetodayaredescendedfromwildplantsfoundintheNearEast,China,SoutheastAsia,andtheAmericas.

HORTICULTURALMETHODOLOGYOvertheyears,humanshavecompiledanimpressivecompen-diumofhorticultural techniques through trial anderror.The


earliestwritten recordsofhorticulturalpracticesare fromthefirstmillenniumb.c.inChina,Mesopotamia(nowcalledIraq),andEgypt,followedbyGreeceandRome.Someofthepracticesmentionedintheseancientwritingsincludetheuseofirontools;manure applications; crop rotation; double cropping; large-scaleirrigationprojects;pollination,pruning, andgraftingof fruit trees;pestanddiseasecontrol;aswellastheidentification,classifica-tion,anduseofplants.Manyofthesemethodsarestillappliedtoday.Thesetextsalsodescribemethodsthatmaynothavebeenincommonuseeveninancienttimes.Similarly,moderntextsonculturalmethodsincludesomepracticesthatarenotwidelyusedbutthathavebeendocumentednonetheless.

AncientEgyptianscreatedformalgardenswithpools,aspiceandperfumeindustry,andcollectionsofmedicinalplants.Mes-opotamiahadirrigatedterraces,gardens,andparks.Significantcontributionstotaxonomyandplant physiologyweremadebytheGreeks.Romansfosteredthedevelopmentofornamentalhor-ticulturewith topiary gardens,andtheyalsousedrudimentarygreenhousesmadeofmicatoforcevegetableproduction.

ThemajorityofthepopularedibleplantswegrowtodaywereculturedbytheseancientcivilizationsaswellasthosefoundinCentral and SouthAmerica. Many cultivars (cultivated variety)weregeneratedfromwildplantsby2000b.c.Sinceourancestorshadaremarkableknowledgeofwild,ediblefoodplants—likelyunsurpassedbycontemporaryhumans—itisprobablethattheysucceededinthecultivationofthemajorityofplantsthatcanbeusedforthispurpose.Comparativelyfewnewfoodplantshavebeendomesticatedinrecenttimes,althoughmanynewvarietiesorcultivarsoftheancientplantshavebeenbredsincethen.

CONVENTIONALVERSUSORGANICPRODUCEConventionalproduceisgrownusingmethodsbasedontech-nologyfromtheindustrialrevolutionandthedevelopmentofagricultural chemistry. Nineteenth-century scientists such as

8 Horticulture

JeanBaptisteBoussingaultandJustusvonLiebigdemonstratedthat plants obtain nutrients from minerals dissolved in water.Thisisthebasisof hydroponics (Figure1.2),asystemwhereplantsaregrownwithoutsoilinasolutionofminerals.Previouslyitwas

Proposed Geographic origins of Edible domesticated Plants

Near East, Egypt, and the Mediterranean – apple, cherry, date, fig, grape, olive, pear, plum, cabbage, broccoli, cauliflower, caraway, leek, carrot, hazelnut, melon, garlic, lettuce, pea, onions, beet, chard, pistachio, almond, dill, parsley, poppy, lentil, carob, and flax

Mountains of Central and Western China – apricot, peach, cucumber, adzuki bean, water chestnut, wasabi horseradish, ginger, cinna-mon, and bamboo

Southeast Asia and the Pacific Islands – grapefruit, orange, lemon, lime, tangerine, banana, mango, clove, nutmeg, black pepper, turmeric, cardamom, sugarcane, coconut, mung bean, taro, and eggplant

Central America – pepper, green bean, squash, pumpkin, sweet potato, sunflower, vanilla, corn, scarlet runner bean, lima bean, pineapple, guava, and jicama

South America – avocado, tomato, potato, chocolate, peanut, cashew, beans, squash, yam, and papaya

The relatively recent domestication of the sunflower, blueberry, strawberry, cranberry, and bramble fruits (raspberry and blackberry) were bred from wild plants of the eastern United States.

Source: Jack R. Harlan, Crops & Man (Madison, Wisc.: American Society of Agron-omy, Crop Science Society of America, 1975).


Figure 1.2 In this photograph, farmers plant lettuce in a hydroponic channel system in a commercial greenhouse. Commercial hydroponic crop production is more expensive than traditional soil-based crop pro-duction, which is why it is less common.

10 Horticulture

believedthatplants“ate”humus (alsocalledcompostororganic

matter).Compostis theresiduefromdecomposedorganicmat-terderivedfromplantsandanimals.Itisnowwidelybelievedthatbothmineralsandcompostcontribute to thegrowthofhealthy plants. Hydroponics methods are often used to pro-ducecommercialgreenhousecropsandaredescribedfurtherinChapter6.

Conventional methods use chemical fertilizers in place ofhumus plus large quantities of pesticides to control insects,microbialdiseases,andweeds.Heavytillage (plowingofthesoil)with oil-fueled machinery to reduce human labor and largefieldsplantedwithasingletypeofcropyearafteryear,aprac-ticereferredtoasmonocropping, werealsointroduced.Themainbenefittomonocroppingisthatplantsallgrowatthesamerate,havethesamewaterandnutrientneeds,andcanbeharvestedatthesametime.Thishelpstoreachthegoaloftheconventionalapproach,whichistomaximizebothyield andprofit.

Vegetables and fresh-cut flowers were traditionally growninfieldsclosetotheirmarkets;thegrowershadawidevarietyofproduce.Farmfieldsbecamelessdiversewiththeadventofgoodroadnetworksandrefrigerationtechnologiesthatallowedforproducetobeshippedtodistantpartsofthecountry.Theincrease in competition from regions with mild climates andlonggrowingseasonscausedothergrowerstospecializeincropsthattheycouldgrowmoreeconomicallyintheirarea.

Although the use of conventional methods may initiallyresult in higher yields than the old-fashioned methods, thereare problems with regard to long-term use since it decreasessoilfertilityandcauseswaterpollution.Thedrawbackstothismethodwerenotimmediatelyapparent,butwenowknowthatover time the heavy use of chemical fertilizers and pesticidesharmsthemicrobesinthesoil,whichultimatelyreducesyieldbycausinginfertility.Themicrobesinthesoilaredirectlyrelatedto the availability of nutrients for plant growth. Soil infertil-ityleadstoweakplantsthataremoresusceptibletomicrobial


pathogensorinsect infestationandthusrequiretheapplicationofmorepesticides.

Many pesticides contain chemicals that are toxic to wild-lifeandhumansandthatpersistintheenvironmentforyears.Insecticides influencetheevolutionofthetarget insect, whichbecomesresistanttothechemical.Thisnecessitatesthecontinualintroduction of new chemicals into the environment (Figure1.3).Entryofthesechemicalsintothegroundwater endangersourfreshdrinkingwatersupplies.Someinsecticidescancausedamagetothenervoussysteminhumans.

Excessive amounts of fertilizer also enter into the ground-water and the surface water. Soluble chemical fertilizers havehistoricallybeenaddedtothesoilinamountsgreaterthantheplantscouldimmediatelyconsume.Heavyrainorirrigationofthecropsdrainssolublefertilizerfromthesoilintotheground-

Figure 1.3 In McAllen, Texas, a plane sprays insecticide on a field of carrots. Although they have been credited for an increase in the agri-cultural production of the twentieth century, insecticides can be toxic to both humans and the environment.

12 Horticulture

waterinaprocesscalledleaching.Manywellshavebeenclosedovertheyearsbecauseofexcessivenitratesthatwereaddedtothesoilasnitrogenfertilizer.

Excessnutrientssuchasnitrateorphosphatemayalsorun offintothesurfacewaterbecauseofsoilerosionfromheavyirriga-tionorrainfallevents.Thiscausesproblemswithexcessivealgal

growth,whichreduceshabitat for fish.Aregion in theGulfofMexicoiscalledtheDeadZonebecauseitbecomesovergrownwithalgaeeverysummerasaresultofnutrientsthatentertheGulffromtheMississippiRiver.Asthealgaedecompose,oxygeninthewaterisusedupandthefishdie.TheDeadZoneisaboutthesizeofthestateofRhodeIsland.

Anadditionalproblemistheuseofheavyequipment,whichcausescompactionofthesoilandresultsinthelossofgoodsoilstructurenecessaryforplantgrowth.Toavoidthisproblemandalsotolessenthepossibilityoferosion,somegrowersdeclinetotillthesoil.Usually,theyinsteadaddlargeamountsofherbicides tokill weedsthatwouldotherwisebedugupbytillage.Someherbicideshavebeenreportedtoaffectthereproductivesysteminanimals.

ORGANICPRODUCEOrganicproduceisgrownwiththeold-fashionedmethodsusedpriortotheIndustrialRevolutioninanefforttostoporreversedamagedonetotheenvironment.Overtheyears,thesemethodshavebeen improved.SirHowardAlbert isknownas the fatheroftheorganicmovement,whichisbasedontheuseofcompost.HedevelopedtheIndoremethodofcomposting,whileworkingasaBritishagronomistinIndiafrom1905to1934.Thebenefitsofcompostascomparedwithchemicalfertilizersincludeimprovedsoil structure, better ability to retain water, higher retention ofnutrientsinthesoil, andtheintroductionof beneficialsoilmicrobesthatsuppresspathogensandhelpplantsobtainnutrients.

The nutrients are released more slowly from compost andarenotleached asrapidlyfromthesoilasarethehighlysoluble


chemicalfertilizers.Compostbeginswithplantresiduesand/oranimalmanuresthatareaged3to6months(Figure1.4).Ani-malandplantresiduesthatwouldotherwisecontributetothepollutionofwaterwaysandlandfillsarerecycledintoalow-costfertilizerandsoilamendment.

BiodynamicmethodswereintroducedbyRudolphSteinerin the 1920s. Specialized compost recipes and soil amend-mentsareusedtodevelopbeneficialsoilmicrobes.Astrologicalconditions,suchasphasesofthemoon,areusedtodeterminewhentosowseedsandtransplant.Thisapproachhasalimitedbut dedicated following worldwide, as does another form oforganiccultivationcalledpermaculture,developedinAustralia

Figure 1.4 Kitchen scraps have been added to the top of this compost pile and should be mixed into the center of the pile with a pitchfork or shovel. Mixing the pile provides for optimal decomposition and discour-ages animal scavengers. Composts are used to improve soil fertility and are made up of organic materials.

14 Horticulture

byBillMollison.Permacultureintegratesthegardenintothenaturallandscape.

J.I. Rodale edited the Encyclopedia of Organic Gardeningin 1959 in response to the American public’s request for anapproachtothecultivationofproducefreefromchemicalresi-dues.Themethodhasbeenpopularwithhomegardenerseversinceandhasgrownsteadilyinthecommercialsectorthroughthe1990sandintothe21stcentury.Thecommongoalwithallorganicapproachesistogrowhigh-qualityproducewhilehavingonlyalowimpactontheenvironment.Themethodscanalsobeappliedinfloricultureandlandscapehorticulture.

Companion plantsandcroprotationsareusedtotakeadvan-tageofnatural interactionsbetweenplants,soilmicrobes,andinsects and thus reduce the need for fertilizer and pesticides.Highgenomicdiversityincropsisencouraged,asitreducesthechanceofdisease-inducedcropfailureandoffersagreaterselec-tionofproducetothegrowerandconsumer.

Theorganicapproachrequiresmoreplanningandcanbemorelabor-intensivethantheconventionalapproach;however,organicproducecanbesoldinthemarketformoremoneythanconven-tional produce. Increased consumer demand for pesticide-freeproducehasresultedinariseinthenumberoforganicfarmsandincreasedthedistributionfromlocalfarmersmarketstoorganicproducesectionsinlargesupermarketchains.

InOctober2002,theUnitedStatesDepartmentofAgricul-ture(USDA)adoptedasetofregulationsforthenationalcerti-ficationoforganicfarms.Priortothis,certificationwasgrantedon a state-by-state or regional basis only. These regulationsprohibitthesaleofgenetically modified organisms(GMOs)undertheorganiclabelbutdoallowforthechemical-andradiation-inducedmutationsusedforplantbreedingpurposes.Addition-ally,theuseofchemicalfertilizersisprohibitedandtheuseoforganicpesticidesistightlyregulated.

Organicpesticidesarederivedfromplantsandothernatu-ral sources. Since some organic pesticide substances may be


toxictohumansandwildlife,theyareusedinsmallquantitiesandonlyasalastresort.Theconsumermaynotknowwhichpesticideswereusedandhowsoonpriortoharvesttheywereapplied;thereforeitisadvisabletoalwayswashyourproducethoroughlytoremovepotentialpesticideresidue.

SUSTAINABLEHORTICULTURESustainable horticulture combines conventional and organicmethodsinanefforttotransitionconventionalgrowerstoamoreecologicallysensitiveapproach.Thisapproachusesknowledgeofthenutrientrequirementsforspecificstagesofgrowthforeachcrop inorder toapply supplemental fertilizers,water,andpestcontrolmeasuresonlyatthetimeandintheamountsneededforthatstageofgrowth.Integrated pest management(IPM) strategiesusebiological controlandcroprotationtoreducepesticideuse.

In1985,CongresssetuptheLISA(LowInputSustainableAgri-culture)program,whichhassincebeenrenamedSARE(Sustain-ableAgricultureandResearchEducation).In1991,SAREandtheEPA(EnvironmentalProtectionAgency)launchedajointventureto reduce agricultural pollution. Although sustainable methodsarepromotedbytheU.S.governmentandland-grant collegeswithextensiveresearchinthefield,theyhaveyettobeadoptedbythemajorityofgrowersintheUnitedStatesbecauseofthefearthatrelianceonorganicmethodswillreduceyieldandbeincompatiblewithsocioeconomicneeds.

SUMMARYThischapterintroducedyoutothe10,000-yearhistoryofhor-ticulture,thegeographicaloriginsofdomesticated,ediblefoodplants,andthemethodologiesusedtogrowthem.Thegeneralprinciplesandphilosophiesofthedifferentmethodsusedintheconventional, organic, and sustainable approaches to growingwerealsodescribed.Thechaptersthatfollowwillacquaintyouinmoredetailwiththeskillsrequiredofahorticulturistandpres-entsomeoptionsfortheprofessionalapplicationoftheseskills.

16

ClassificationofPlants

If you do not know the names of things the knowledge is lost.

—Carolus Linnaeus (1707–1778)Swedish botanist

Can you imagine how confusing life would be if we had no names andeverytimeyouwantedtorefertoaperson,place,orthingyouhadtodescribeitanditsrelationshiptoallothersofitskind?Wearefortunatethatourpredecessorscameupwiththeideaofnames and that knowledge about plants has been successfullypasseddownfromgenerationtogeneration.

Classificationisatermusedtodescribetheprocessofgroup-ingrelatedplantstogetherandnamingthegroups.Thesegroupshavebeenhistoricallybasedonmorphologicalandanatomicalfeaturesand,morerecently,ongenetics.Membersofaspecieshavecharacteristicsthatsetthemapartfromallotherpopula-tionsofplants,andtheynaturallybreedwitheachother.Closelyrelated species with similar characteristics are grouped into agenus.Thegeneraaregroupedintofamiliesandthefamiliesaregroupedintoclasses.Allthelandplantclassescollectivelyformtwodivisions,thebryophytesandthetracheophytes.

Bryophytesarecallednonvascularplantsbecausetheyhaveaverypoorlydevelopedvascular system.Sincethevascularsystemisinvolvedinthetransportofwaterthroughouttheplant,bryo-phytesaregenerally—butnotalways—foundinmoistplacesandgodormantwhenwaterisscarce.Thereareapproximately24,000speciesofbryophytes,mostofwhicharemosses.Theseplantsarenotwidelycultivatedcommerciallybutmaybeofgreatinterestto botanists and naturalists. Mosses may sometimes be foundgrowingonmoistsurfacesingreenhouses.

Tracheophytes have a well-developed vascular system thatenablesthemtogrowtallerthanbryophytesandtosurvivetem-poraryshortagesofwater.Theyaredividedintoseedplantsandseedlessplants.Theseedlessplantsreproducebysporesandmanyarefoundinwethabitats.Fernsareseedlesstracheophytesthataresometimesgrowningardensorashouseplants.

Tracheophytesthatproduceseeds aredividedintotwogroups,the gymnosperms and the angiosperms. Gymnosperms areplantsthatproduceseedsthatarenotenclosedinanovary,such

18

ClassificationofPlants

19classification of Plants

as the cycads,gingko, conifers, andgnetinae.Thecycadshavepalmorfern-likeleavesandproducecones.Gingkotreeshavebroad,deciduousleavesandstinky,fleshyfruits.ConiferssuchasthePinus spp. (pines)andPicea spp. (spruce)haveneedle-likeevergreen leavesandproduceseedsin cones,whereasJuniperus spp.(junipers)mayhavescale-likeleavesandproducetheirseedsinberries.Thegnetinae,whichincludeEphedra spp., havexylem

vesselssimilartothosefoundinmosses,horsetails,andferns.Ofallthegymnosperms,theconifersarethemostwidelycultivated.Gingkotreesarealsooftenusedforlandscaping,especiallyalongroadsandinpublicplaces.

Angiospermsareseedplantsthatproduceflowers.Theseedsareenclosedinamatureovary,whichformsafruit.Therearemore than 250,000 species of angiosperms; this group is themostwidelycultivatedgroupofplantsonEarth.Angiospermsaredividedintotwoclasses,themonocotsandthedicots,basedonmorphologyandanatomy.Monocotshaveseedswithasinglecotyledon;dicotseedshavetwocotyledons.Thesetraitsarethebasisforthesegroups’names:monocotisshortfor“monocotyle-don”(mono-means“single”)anddicotisshortfor“dicotyledon”(di-means“two”).Thepartsofmonocotflowers(sepals,petals,stamens, ovary) usually occur in multiples of three, whereasthe parts of dicot flowers are found in multiples of four orfive.Additionally,monocotleaveshaveparallelvenation.Dicotleaves have net venation because of the arrangement of theirvascularsystem. Figures2.1and2.2showsomeof thediffer-encesbetweenmonocotanddicotplantparts.

Thevascularsystemisatransportationnetworkofconnectedcells that form tunnels in the plant that extend from the rootsthroughthestemtotheleaves,flowers,andfruits.Xylemtrans-portswaterandmineralsupwardsfromtherootsanddistributesitthroughouttheplant.Phloemtransports thesugarscreatedbypho-

tosynthesis fromtheleavestootherpartsoftheplant.Thesetunnelsarebundledtogetherandcanbeseenastheveinsonaleaf.

20 Horticulture

Figure 2.1 (TOP) The lily is an example of a monocot with flower parts typically found in multiples of three. There are three outer sepals, which in this example look identical to the three inner petals. The stigma has three lobes and there are six stamens. Florists will often remove the anthers from the stamens because they shed large amounts of pollen. (BOTTOM) The veins of leaves of monocots, such as this lily leaf, run parallel to each other.


Figure 2.2 (TOP) The hibiscus flower is a dicot with five petals, five small green sepals, a five-lobed stigma, and many yellow stamens fused to the style. (BOTTOM) This hybrid camellia is a dicot with a rose-like flower. The veins of leaves of dicots form a net-like pattern, known as net venation.

22 Horticulture

Themonocotanddicotclassesare subdivided further intofamilies.Membersofbotanicalfamiliessharesimilarcharacter-istics. For example, plants in the Lamiaceae family have char-acteristicallysquarestems,andmanyhavetrichome hairs.Thesehairs can make the leaves or stems feel rough, and they helpreduceairflowacrossthesurfaceoftheleaf.Glandulartrichomehairsecretesessential oilsandresins,whichcanmakethesesur-facesstickyorfragrant.Manymedicinalandculinaryherbs,suchasmint,sage,lavender,andthyme,aregrownfortheirabilitytoproduceessentialoilsandresins.

Plants in the family Solanaceae produce mildly to highlypoisonousalkaloidsandhavesimilarflowers.TheintroductionoftomatoandpotatocropsfromtheAmericastoEuropetooksometimebecauseofthereputationoftheirhighlytoxicrela-tives,suchasthedeadlynightshade.

Plants in the family Leguminosae also have similar flowersandproducefruitscalled legumes.ThepeaflowerandpeapodsareexamplesofLeguminosaeflowersandfruits.Manyoftheseplantsalsohaveimportantrelationshipswith soilbacteria thatarecapableofnitrogen fixation.Thebacteriaformnodulesintherootsoftheplants.

Seedcatalogs,plantencyclopedias,andgardencentersoftengroupplantsinwaysotherthanbyfamily—forexample,bylifecycle, edibility, cultural requirements, or geography. Life cyclecanbeannual,biennial,orperennial.Annualplantsflowerandsetseedinthefirstyearandthendie.Theygenerallybloomallsummerbutneedtobereplantedeveryyear;sometimestheywillself-sowiftheflowershavebeenallowedtogotoseed.Biennialsflowerandproduceseedinthesecondyearandthendie.Peren-nialstaketwoormoreyearstoflowerandsetseed,andtheyliveformanyyears.Theygenerallybloomeveryyearafterthefirstflower.Perennialsusuallybloomforashortperiodeachseasonandthen dieback untilthefollowingspring.Theycanbeshort-lived(fourtofiveyears)orlong-lived(manythousandsofyears)likethebristleconeandSequoiapinetrees.


the Wide World of AngiospermsThere are approximately 250,000 known species of angiosperms. The table below lists angiosperm plants divided into the dicot and monocot classes and further divided into families and genus. The binomial nomenclature is in italics and the common name is in parentheses. The approximate num-ber of species is listed after the common name. Each species may have numerous cultivars (the daylily has over 30,000) that are developed for specific traits and adapted to different growing conditions. Some cultivars improve crop yield and others are grown because of their unique appear-ance or taste.

Source: Christopher Brickell and Judith D. Zuk, The American Horticultural Society A–Z Encyclopedia of Garden Plants (New York: DK Publishing, 1996).

DICOT PLANTSLamiaceae Lavendula spp. (lavender) 25 Mentha spp. (mint) 25Salvia spp. (sage) 900Thymus spp. (thyme) 350

Leguminosae Glycine max (soybean)Medicago sativa (alfalfa)Phaseolus vulgaris (common bean)Pisum sativum (garden pea)

RosaceaeFragaria spp. (strawberry) 12Malus spp. (apple) 35Prunus spp. (plum, peach, cherry, almond) 200Pyrus spp. (pear) 30Rubus spp. (raspberry, blackberry) 250

SolanaceaeCapsicum annuum (chili, sweet pepper) Lycopersicum esculentum (tomato)Solanum tuberosum (potato)

MONOCOT PLANTSAmaryllidaceaeAllium cepa (onion)A. sativum (garlic)Narcissus spp. (daffodil) 50

Liliaceae Hemerocallis spp. (daylily) 15Lilium spp. (lily) 100Tulipa spp. (tulip) 100

PoaceaeFestuca spp. (fescue) 400Poa spp. (bluegrass) 500Zea mays (sweet corn)

24 Horticulture

Deciduousplants losetheir leaves inthefall,whereasever-green plants retain their leaves year round. Some deciduousplantshavebrilliantdisplaysofcolorfulfoliage inthefallpriortoleafdrop.Thisisduetothecarotinoidpigments,whicharecoloredinshadesofredandyellow.Thegreenchlorophyllpigmentsaremorenumerouswhentheplantisgrowing,soduringthistimecarotinoidpigmentsaremaskedbythegreen.Whentheplantgetsreadytogodormant,itstopsproducingchlorophyllandtheredandyellowpigmentsbecomevisible.

Culturalrequirementsincludetheamountofsunandwaterrequiredbyplants,thepreferredtemperatureandsoiltype,andnutrient needs as described in Chapter 4. Xeric plants surviveperiodsofdrought;theyareadaptedtohot,drysummersandcool,moistwinters.Shadeplants,asyoumayhaveguessed,liketobeshadedfromthesummersun.Vegetablesareoftenseparatedintowarm-seasonandcool-seasoncropsbasedonthetempera-turesatwhichtheirseedsprefertogerminate.Grassesarealsoclassifiedaswarmorcoolseason.Annualflowersaresometimeslabeledasfrosttolerantorfrostsensitive.

Nativeplantsarethosethatarebelievedtohaveoriginatedintheregionwheretheyaretobecultivated.Generally,thecultiva-tionofnativeplantsrequireslessworkbecausetheyarealreadyadapted to the soil and climate. Plants may also be groupedaccordingtotheecosystemwheretheyarefoundgrowingwild,such as alpine, tropical, desert, or riparian. Alpine plants arefoundathighaltitudes,tropicalplantsinrainforests,andripar-ianplantsbyriversandstreams.

PLANTNAMESManyplantshavebeengivencommonnames.Thesetendtobelocallyderived,somultiplenamesmayexist forasingleplantspeciesifitgrowsnaturallyindifferentpartsoftheworld.Therearealsoinstanceswherethesamecommonnameisusedfordif-ferentplants.Thymeisthecommonnameusedformorethan350speciesinthegenusThymus.Onlyafewofthesespeciesare


What Exactly Is a Fruit? Some foods we commonly think of as vegetables, such as the tomato or pea pod, are actually, botanically speaking, fruits. Peppers, squash, eggplant, cucumber, and sweet corn are also technically fruits. Fruits are formed after fertilization as the ovary ripens; while it develops, the other flower parts wither and die. The wall of the ovary becomes the pericarp (the outer layer of the fruit) and the fertilized ovules turn into seeds. Fruits can be fleshy or dry.

FLESHYFRUITSThe drupes (olive, plum, cherry) develop from a single ovary with a single ovule that becomes the pit. Pome fruits (apple, pear) grow from a compound ovary with many ovules and have distinct chambers with many seeds. Berries (tomato, pepper, grape) also have many seeds. Pepo fruits (melon, pumpkin, squash, cucumber) are fleshy with many seeds and a hard rind. Raspberries, strawberries, and blackberries are fleshy aggregate fruits that form from the fusion of many flowers. Parthenocarpic fruits do not develop seeds and can occur naturally (banana) or be chemically induced (oranges, watermelon).

DRYFRUITSDry fruits that break open to free the seeds while still attached to the plant are described as dehiscent. Some examples are legumes (pea pod), which develop from a single ovary that splits down both sides and capsules that grow from a compound ovary and open at the top (poppy). The pericarp of indehiscent fruits remains closed until after it falls off the plant; examples of these types of fruits are corn and nuts.

used for culinary purposes, so it is important to purchase thecorrectplantifyouwanttoeatit.

Horticulturists use a system of binomial nomenclature andcultivarnamestoidentifyaspecificplantandthusavoidthecon-fusionthatcanbecausedbycommonnames.Binomialnomen-clatureisasystemthatassignsauniquetwo-wordnametoeach

26 Horticulture

species,madeupofagenericname(thegenus)plusaspecificnamethatdefinesthespecies.ItwasdevelopedbyCarolusLin-naeusintheeighteenthcentury(Figure2.3).Linnaeusbuiltupontheworkofmanypriorbotanists.Theearliestrecordsmadebythefathersofbotanydatefromthefifthcenturyb.c.tothethirdcenturya.d.andrecountknowledgefromMesopotamia,Egypt,Greece,andRome.ArabandAsiaticbotanicalrecordsfromtheeighthtothetwelfthcenturya.d.andtheworkofbotanistsfromthe1500stothe1700swerealsodescribedbyLinnaeus.

BinomialnomenclaturewascreatedinLatin,asthiswasalan-guagecommontobotanistsfromdifferentcountries.ThegenusnameisaLatinnounthatmaybethenameofapersonwhodis-coveredtheplantoritmaysomehowdescribeacommontraitofalltheplantsinthegenus.ThespeciesnameisaLatinadjectivethatmodifiesthenounbasedonaparticularcharacteristicofthespe-cies,suchasthecoloroftheflowersorsizeoftheplant.Thegenusisalwayscapitalized;thespeciesnameisinlowercaseandthefullnameiseitheritalicizedorunderlined.(Forexample,thebinomialnameforcornisZea mays.)Thegenuscanbeabbreviatedbythefirstletterfollowedbyaperiodininstanceswhereithasbeenpre-viouslyreferredtoinamanuscript.Sometimesthespecificepithetisdesignatedassp.orspp.(plural)incaseswhereitiseithernotknownorifthewriterwantstorefertoallplantsinthegenus.

Thebinomialnomenclature,orLatinname,maybemodi-fiedtoreflectabotanicalvarietyorahorticulturalcultivar thatis noticeably different from other plants of the same species(thoughallmembersofaspecies—includingtheuniquevariet-iesandcultivars—can interbreed).Themodificationaccountsfordifferencesthatoccurinplantsbecauseofgrowthinvarioustypesofsoilorspontaneousmutationsthatmayproduceadif-ferentcolorflowerorvariegatedleaves,amongothertraits.

Varietiesareplantspecimensidentifiedintheirnaturalenvi-ronment, whereas cultivars are those that were cultivated andbredbyman.However,manysubspeciesofvegetablesarecalled


varietiesandthetwotermsareoftenusedinterchangeably.Thecultivarorvarietynameissetinsinglequotes,isnotitalicized,andislimitedtothreewords.Thecultivarnameeitherfollowsthebinominalorisusedinplaceofthespeciesname.Collectionsofcultivarsmaybecombinedintolargerhorticulturalgroups.

Figure 2.3 Carolus Linnaeus was a Swedish botanist and taxonomist, referred to as the father of modern taxonomy. In 1749, Linnaeus laid the foundation for the classification of living organisms when he introduced binomial nomenclature.

28 Horticulture

Examples of Latin names, followed in parentheses by thecommonname(s),fortheculinaryspeciesofthymeincludeThy-mus vulgaris(commonthyme,gardenthyme),T. herba-barona(carawaythyme,herbbaron)andThymus × citriodorus (lemon-scentedthyme).The×inT. × citriodous isusedtodesignateitasahybrid.Hybridsarearesultofcross-breedingasdescribedinthenextchapter.T. serpyllum ‘Coccineus’(redcreepingthyme)isnotanedibleplantbutisappropriateforuseinagardenpathorrockgardenbecauseofitscreepinghabit andcolorfulflowers.Theword‘Coccineus’setinsinglequotationmarksindicatesthatitisacultivar name.

Plantsneedtobedescribedbeforetheycanbeidentified.Plantanatomicalandmorphologicalcharacteristicsareusedtogener-atedescriptionsofplantsandtogroupthemaccordingtotheirsimilaritiesinordertoidentifyandnamethem.Thebesttimestodescribeplantsarewhentheyareinfullflower.Alternately,fruit-ingstructureswillyieldagreatdealofinformation.Theorderofthedescriptionfollowsthegrowthoftheplant.Itbeginswiththeroots,movestothestemandleaves,andendswithadescriptionofthereproductivestructures(flowersandfruits).

Oncethesefeatureshavebeennoted,onecanconsultabotan-icaltextwithadichotomouskey,fieldguides,illustratedency-clopedias, seed and plant catalogs, garden centers, botanicalgardens,andherbariumsfordescriptionsofsimilarplantsthathavebeenpreviouslyidentifiedandnamed.Adichotomouskeyconsistsofpairedstatementsthatdescribethecharacteristicsofaplant.Oneofthestatementswillapplytotheplantanddirectstheusertoanothersetofpairedstatements.Thiscontinuesuntiltheplantisnamed.Pictures,illustrations,ordriedspecimenscanbeveryhelpfulintheidentificationofplants.

Dried specimens are made by pressing the whole plantbetweensheetsofpaper,thenmountingwithglue.Herbariumsarecollectionsofpressed,driedplantsthathavebeenidentifiedbybotanistsandcanbefoundinbotanicalgardens,atuniversi-ties,andinprivatecollections(Figure2.4).Driedspecimenscan


bebroughttoanherbariumforidentificationbycomparisontootherplantsinthecollection.

SUMMARYThis chapter presented a classification of horticultural plantsaccording to division, class, family, genus, and species, withan emphasis on the angiosperms—the most widely cultivatedgroup of plants—and described the binominal nomenclaturemethodfornamingplants.Otherpopularmethodsforgroupingplantswerealsopresented.Itisimportanttoknowhowplantsarerelatedtooneanotherandtheenvironmentswheretheyarenaturally found,as thisgenerallyhelps inunderstandingtheirculturalrequirementsandindeterminingwhichplantsshouldbe grown together. Plants of the same species will interbreed.PlantpropagationandbreedingarethetopicsofChapter3.

Figure 2.4 Botanists are photographed in Guyana as they identify and catalog plant specimens for an herbarium. An herbarium is a collection of preserved plant specimens.

30

PropagationandBreeding

Animals are not essential; plants supply over 90% of the food consumed by humans.

--Jack Harlan, The Living Fields (1995)

Seed formation is initiated by changes in environmental conditions, such as the difference in daytime and nighttimetemperaturesandtherelativenumberofhoursofdaylightver-susdarkness,andalsobytheproductionofplanthormones.Theprocessbeginswiththedevelopmentofflowerbuds.Pol-linationoccursaftertheflowerbloomsandinvolvesthedeposi-tionofthemalepollenontothefemalestigma.Pollinationisfollowed by fertilization, which is required to produce viableseeds. Fertilization occurs when sperm cells from the pollengrainreachtheovulesintheovaryandcombinewithanegg.Thefertilizedeggdevelopsintoaseedthatcontainsanembry-onic plant in a dormant state. Reproductive structures areillustratedinFigure3.1.

PROPAGATIONOFNEWPLANTSFROMSEEDSSeedsaredormant,embryonicplantsdevelopedfromfertilizedovules.All seeds contain an embryonic stem, an embryonicroot,andmeristems.Theseedissurroundedbyaprotectiveseed coat. In addition, monocot plants have a single largenutritiouscotyledon,whereasdicotshavetwonutritiouscoty-ledons. The cotyledons supply food to the seedling until itbeginsphotosynthesis.

The most important factors for seed germination are aproperlyprepared seedbed, consistentmoisture, andadequatetemperature.Seeds fromdifferentplantshaveawiderangeoftemperatures and moisture conditions required to break dor-mancy. Dormancy occurs to protect the plant embryo fromemergenceunderadverseconditionsthatcouldkillitwhileitisstillyoung.Theconditionscanbequitespecificandareprovidedwiththeseedswhentheyarepurchased.

Temperature requirements range significantly; some plantsrequirevernalization,whereassomewillnotgerminateunlesstheyhavebeeninvolvedinafire,suchastheseedsofthePonderosapine.Plantsthatrequirevernalizationmustbeexposedtocold

32

PropagationandBreeding

33Propagation and Breeding

or freezing temperatures for a set length of time, followed byexposure towarmtemperature.Thishappensnaturallyas theseasonprogressesfromwintertospring.

Pretreatmentsmaybeapplied.Seedsaresometimesboiledinwatertokillvirusesortreatedwithpesticidestoinhibitdiseasesthatwouldkilltheseedling.Seedsthatneedcoldtreatmentcanbeputinacoolerorfreezerorplantedinpottingsoilandput

Figure 3.1 The female reproductive organ is called the carpel. The car-pel is made up of a stigma and ovary connected by the style. The male reproductive organ is a stamen. The stamen consists of anthers, which contain the pollen grains, suspended on a thin filament. Pollen grains land on the stigma, which has a sticky surface, and develop a pollen tube that grows downward through the style until it reaches the ovary. The ovary contains ovules (eggs), and the pollen grains produce sperm. The sperm cells travel down the pollen tube and fertilize the ovules. The ovary grows into a fruit and the other parts wither away.

34 Horticulture

outsideoverthewinter.Theycanalsobesowninthegroundafterthefirstfrostsotheywillgerminateinthespring.

Seedsofcool-seasonplants,suchaspeasandcarrots,canbeplantedoutdoorsearly in thespring.Warm-seasonplants liketomatoesandpeppersaremoresensitivetolowertemperaturesandcanbestartedindoors(inahouse,greenhouse,hotbed,orcoldframe)andtransplantedintothegardenafterthelast aver-

age frost date.Cool-seasonvegetablesarecharacterizedashardy

Specialized Flowers and PollinationPollination occurs in several different ways, depending on the structure of the flower:

Plants that self-pollinate are called selfers. For example, the reproductive structures of pea flowers are enclosed between two fused petals, called a keel, which ensures that self-fertilization takes place.

Wind-pollinated plants, such as trees and grasses, generally produce large amounts of small, light pollen that is not sticky. The flowers are not usually colorful, do not produce nectar, and have no odor. The flowers form before the leaves do and the stamens and stigmas are exposed to the wind. When these flowers are blown about by the wind, the pollen shakes loose from the anther of one plant and is deposited on the stigma of another plant. Most pollen can be carried up to 330 feet (100 meters) from the plant. These types of flowers are usually found in temperate regions and are rare in the tropics.

Insect pollinators pick up pollen grains as they feed on nectar from one plant and deposit it on subsequent plants that they visit. The flowers pol-linated by insects tend to have sticky pollen that adheres to the hairs on the legs of the insects. There are approximately 20,000 species of bees attracted to sweet-scented flowers that produce nectar and 16 families of beetles that are lured to flowers with fruity, spicy, or pungent odors. Flies


orhalf-hardyandwarm-seasonvegetablesastenderorvery tenderbasedontheirabilitytotoleratefrost.

Frostoccurswhenthetemperaturedropstofreezing(32°F)orbelowandisvisibleasawhitesubstancethatneedstobescrapedoffofcarwindshieldsinthemorning.Itisfrozenwatervaporandcandamagesensitiveleaves.Frostpocketsareregionswherecoolairsettles,suchasatthebottomofahill,andarepronetofrostearlierandlaterintheseasonthenotherareas.Youcanfind

also pollinate flowers as they feed. Butterflies have a long, thin proboscis to suck nectar from tubular flowers or flowers with a long style, but the pollen tends not to stick to their bodies and so they are not efficient pollinators (Figure 3.2).

Figure 3.2 A butterfly uses its proboscis to suck nec-tar from a thyme flower.

36 Horticulture

outyourlastaveragefrostdatefromtheUnitedStatesNationalArboretumWebsitelistedintheFurtherReadingsectionofthebook.Yourlocalcooperativeextension(describedinChapter8)oralocalgardencentercanalsoprovidethisinformation.

Seeds that are sown directly in the garden will need to bewatereddailyforatleastseveralweeksunlessthereissufficientrainfalltokeepthegroundmoist.Theseedsonlyneedtobekeptmoist;heavyrainfallorirrigationmaywashthemaway.

Seeds that are started indoors are planted in germinationmedia insmallpotsor flats andprovidedwithsupplementalheatandlightduringlatewinterandearlyspring.Germinationmediaisformulatedfrommaterialsthatabsorbwaterandstaymoist,suchaspeatmoss,whichisfoundinbogsandharvestedforsaleatnurseries.Somepeopleareopposedtotheharvestofpeatmossbecauseittakesalongtimetogrowinthewild,and will use other substances such as coir from coconuts orawell-ripenedcompostthathasbeenpassedthroughafine-meshscreen.

Germinationmediamaynotprovidemanynutrientsbecauseitisassumedthattheseedlingswillbetransplantedintoamorenutritioussoilorpottingmixshortlyaftergermination.If thepots or flats are placed inside a plastic bag or covered withglass, theplantsremainmoistandwillnotneedtobemisted.Theplasticorglasscreatesaminiaturegreenhouseandretainsthemoisturefrompresoakedgerminationmedia.Commercialgrowershavededicatedgerminationroomsthatsupplythenec-essaryheatandhumidityandalsosupplementallightforseed-lingsthathavedevelopedtheirfirsttrueleavesandhavestartedphotosynthesizing.

PROPAGATIONFROMCUTTINGSPlants produced from cuttings will be clones of the parentplant. Clone is the Greek word for “twig” and describesplants that are reproduced without the benefit of sexual


recombination;therefore,the genomeoftheoffspringisiden-ticaltotheparent.Cuttingscanbetakenfromthestem,leaves,or roots.Stemor shootcuttingsarecommonlyused for thepropagationofhouseplants,cutflowers,woodyornamentals,andorchardtrees(Figure3.3).

Figure 3.3 Stem cuttings from a woody ornamental (Pyracantha) that have developed adventitious roots. Cuttings taken from the same plant will be genetically identical to the parent and to each other.

38 Horticulture

Acutismadejustabovethenode,whichisthejunctionofastemandleaf.Acalluswill formatthepointofthecutandadventitious rootswillgrowfromthestem.Somespecieswillmorereadily formroots fromcuttings thanothers.Theprocesscanbe accelerated by the application of root hormones. Cuttingscanalsobetakenfromstemmodifications,suchastubers.Mostfamiliaristhepotato,whichsproutsfromtheeyesonatuber.Thetubersarecutintopiecessothateachpiececontainsaneye;theseareusedasseedplants.Plantsthatformbulbousstems,suchasonions and tulips, produce multiple bulblets that are dug up,divided,andtransplanted.

Stolons, foundon strawberryplants, areaboveground stemmodificationswithnodesthatgenerateadventitiousrootsandshoots when they come into contact with the soil and can beused to generate new plants. Rhizomes are modified under-ground stems; some are edible (for example, ginger). Thosefoundontheirisandmanygrassplantsarenotedible.Weedsthatreproducewithrhizomesmaybecomeinvasiveanddifficulttocontrolbecauseiftheentirerhizomeisnotremovedtheplantwillregenerateitself.

Grafting is a method that involves the combination oftherootstockfromoneplanttothescion(stemcutting)ofasecond. The rootstock is usually from plants that have beenwell established in the orchard or vineyard. They may haveexcellentdisease resistanceor someothercharacteristic thatmakes them vigorous growers. The rootstock includes therootsandthelowerportionofthestem.Thescionisfromaplant that produces a fruit with a new trait that the growerwantstoreproduce.Inasuccessfulgraft,thevascularsystemswillcombineandthescionwillgrowandsetfruitonthehost’srootstock.Thisprocedure isoftenusedwithappletreesandgrapevines.


TISSUECULTURESomeornamentalplants,includingorchidsandmosttransgeniccrops,arereproducedbytissueculture(Figure3.4). Thisinvolvestheinflictionofawoundtotheparentplantsothatitformsa

callusfromparenchymacells.Parenchymacellsaremostsimilar

Figure 3.4 Round-leaved sundews (Drosera rotundifolia) are grown from tissue cultures on a gelatin media in a petri dish. In this process, known as micropropagation, clones are grown from single cells of a cal-lus that formed from a wound inflicted on the parent plant.

40 Horticulture

tomeristemcellsandrepresentupto80%ofallthecellsintheplant. Meristem cells have a large nucleus and can repeatedlydivide to produce daughter cells. Meristem cells are the plantequivalentofanimalstemcellsandarefoundinthemeristemregionatthetipsofrootsandshootsandinseeds.Itisonlywhenmeristemcellsmigrateoutofthemeristemregionthattheydif-ferentiateintospecializedcellsthatmakeuptherestoftheplant.Onceameristemcelldifferentiates,itgenerallywillnotdivideagain,butparenchymacellscandivideinresponsetoawoundandproduceacallus, whichisamassofundifferentiatedcells.Theseundifferentiatedcells fromthecalluscanbe inducedtodifferentiate into the specialized cells that will produce a full-grownplant.

Thecalluswillgenerateasomatic embryowhengrownonanutritiousgelatinousmediasupplementedwith hormones.First,thecallusisplacedina receptaclecalledapetridishthatcontainsamixofchemicalnutrients,highconcentrationsofcytokinin,andlowconcentrationsofauxin,allofwhichhavebeensolidifiedwithgelatin.Thisratioofhighcytokinintolowauxinpromotesshootgrowth.Aftertheshootsareformed,theplantletsaretrans-ferredtoasecondpetridishwithahighauxintolowcytokininratio,whichinducesrootgrowth.Afterrootgeneration,theyaretransferredtopottingsoil.

TRANSPLANTINGTransplantingissimplythetransferofaseedlingoryoungplantfromonecontainertoanotherorintotheground.Someplants,such as those that form taproots, would rather not be trans-plantedandshouldbesownwheretheyaretogrow.Taprootsareenlargedprimaryrootsthataresometimesusedforfoodstorage.Carrots and parsnips are examples of swollen taproots. Somehorticulturistsbelievethatmultipletransplantsintonutritiouspottingmediaorsoilwillbenefittheplantandgivehigheryields.


Othersthinkthattransplantingcausesshocktotheplantandwillcauseittobelessvigorous.Bothoftheseviewpointsarecorrectwhentakeninthepropercontext.

Whetherseedsaresowndirectlyinthegroundwheretheywillgroworaretransplantedfromcontainertocontainerdependsupon the type of roots formed by the plant and its culturalrequirements,aswellasthetypeofsoilandclimate.Rootscanbedamagedintheprocessandmayhavetroubleaccessingnutri-ents,especially if thesoilbedhasnotbeenproperlyprepared.Phosphorousfertilizerisoftenapplied,asitisthemostdifficultnutrientfordamagedrootstoaccessanditpromotesdevelop-mentofnewroots.

PLANTBREEDINGCropsthatrelyonwindorinsectpollinationbutaregrowninagreenhousemayhave tobepollinatedbyhand.Cultivatedplantsmaybehand-pollinatedwithasmallpaintbrush.Thehorticulturist brushes the anther of the stamen to retrievepollen grains and then deposits them on the stigma of thefemalefloweronanotherplant.Handpollinationisalsousedto cross-pollinate plants to create new hybrids. Plants thatbelongtothesamespecies,includingallthesubspecies(vari-eties or cultivars), will naturally interbreed with each othertoformhybrids.TheapproachtoclassificationdevelopedbyLinnaeus,describedinthepreviouschapter,gaveinsightintothe relationship between speciation and plant breeding thatwasdevelopedfurtherbytheworkofCharlesDarwininthe1800s.

LutherBurbankwasaprolificplantbreederwhowasinspiredbyabookwrittenbyDarwinin1868calledThe Variation of Ani-mals and Plants Under Domestication.Burbankbredhundredsofnewcultivars;thefirstofthesewastheRusset(orBurbank)potato in1873.He then importedberries,plums,andnuts to

42 Horticulture

Californiaandexperimentedwithwidecrossesbetweendomes-ticandforeigncultivars.Widecrossesdonotnaturallyoccurandhaveunpredictable results thatoftencausemutations thatareharmfultotheplant.Therefore,thismethodinvolvesthepropa-gationandscreeningofmillionsofplants to findonehealthycultivarwithadesirablenewtrait.

Chemical-andradiation-inducedmutationswereintroducedinthe1900s.Theplantisexposedtocertainchemicals,X-rays,or gamma radiation, and this treatment produces unpredict-ablemutationstothetargetplant.Whenthemutationoccursin a somatic (nonreproductive) cell, the mutation may affecttheplantitselfbutnottheoffspringunlessthesomaticcellsareusedtoclonenewplants.Whenitoccursinagermcell(spermoregg),themutationispassedtotheoffspring.Mostofthesemutationsarenotbeneficialtotheplantortohumanssothismethodalsorequiresthepropagationandscreeningofmillionsofplantstoestablishausefulnewcultivar.Rioredgrapefruitandwheatarecommercialcropswithradiation-inducedmuta-tions.Achemicallymutatedbarleycultivar,introducedin1995,iswidelyusedinbeerandamutatedcommercialpeanutcultivarwasbredin1959.

Transgenicplants areplants thathavehadgenes fromanunrelatedorganisminsertedintothechromosomebygenetic

engineeringforthepurposeofbreedinganewcultivar(Figure3.5).Sourcesofthesegenesincludeotherplants,microbes,andfish.Thegenesthathavebeenusedtotransformplantscodefor traits such as resistance to specific microbial infections,resistance to cold temperatures, resistance to drought andsalt,parthenocarpy,resistancetoherbicides,andthecreationofpesticides.

Themostcontroversialtransgenicplantsarethosethatcre-atepesticides.Governmentregulatoryagenciesclassifythegeneproductasapesticideandnotafoodadditive;therefore,theFDA


Figure 3.5 Genetically engineered crops, or products involved in ongo-ing or planned transgenic studies, are photographed above. Genetic engineering, the process of manipulating genes, remains a controversial issue around the world.

44 Horticulture

(FoodandDrugAdministration)isnotinvolvedintheestablish-mentof safetyguidelines forpesticide residue in transformedcrops.

Biologists cannot control where on the chromosome theintegrationoftheinsertedgeneoccurs,andtheprocesswillmostlikelycauseaproblembyinterferingwiththefunctionofotherimportantgenes.Becauseofthis,geneticengineeringoffersnotime-orlabor-savingadvantageoverwidecrossesandchemical-orradiated-inducedmutations,asthisprocessalsorequiresthepropagationandscreeningofmillionsofplantstocomeupwithahealthynewcultivar.

The unpredictable results obtained from wide crosses,chemical-andradiation-inducedmutations,andgeneticengi-neeringmaybearesultoftransposableelements.Transposableelements are naturally occurring, mobile segments of DNA(deoxyribonucleicacid).Theyplayanimportantroleingeneticengineering.Transposableelementscancauseawholesegmentof chromosome to be duplicated, moved to another chromo-some,orevendeleted.Thegenomecanberadicallyalteredandtheresultisoffspringthataredifferentfrombothparents.Trans-posableelementsarefoundinallgenomesthathavebeenstudiedtodateandareinhibitedbynaturallyoccurringmodificationstotheDNA.Thesemodificationsmaybeinheritedandpreventtheactivityofthetransposableelement.TransposableelementscanbetriggeredbyX-rays,gammarays,widecrosses,andtissueculturetechniques,whichexplainstheunpredictableresultsofbreedingmethods.

Ithasbeen suggested thata rise in thenumberofpeoplesusceptibletofoodallergiesmaybeattributedtotheintroduc-tionofnewcultivarsbredwithmethodsthatcantriggertrans-posableelements.Peanuts,wheat,soy,andbarleyareexamplesofcropsthatmayhaveacquiredsubtlemutationsthattriggerallergies. Extensive research would be required to confirmwhetherthisisthecase.


SUMMARYThischapterprovidedanintroductiontothemethodsinvolvedinplantbreedingandpropagation.Thebreedingofplantsthatareresistanttodiseaseisveryimportant,asithelpstoreducetheamountofpesticidesthatmustbeapplied.Itwasshownthatregardlessof themethodused forbreeding,millionsofplants must be propagated before a useful cultivar can beestablished. This illustrates why the science of horticulturetookmanythousandsofyearstoestablish.

46

CulturalRequirements

Not every soil can bear all things.--Virgil (70 B.C.–19 B.C. )

Ancient Roman poet

If you only ate one meal a week, do you think you would grow as tall asyouwouldotherwise?Howlongcouldyoulastwithoutwaterorair?Weallhavebasicrequirementsnecessarytomaintainahealthybody.Theseincludeoxygen,water,carbohydrates,andothernutri-ents.Plantsarenodifferent.Theyrequirethesethingsaswell,anditisthejobofthehorticulturisttomakesurethattheygetthem.

Wegetouroxygenfromtheatmosphere.Sodoplants,butitmustfirstdiffuseintothesoilbecausetheyrespireor“breathe”with their roots. For this reason, there must be a balance ofair and water in the soil. Many plants die from overwateringbecausetheydonotgetenoughoxygen.Ontheotherhand,iftheplantdoesnotreceiveenoughwater,itwiltsandeventuallydiesbecauseitaccessesnutrientsfrommineralsdissolvedinthewaterandbecausewaterisnecessaryforphotosynthesis.

We get carbohydrates from eating plants. Plants, however,maketheirowncarbohydrateswithphotosynthesis.Photosyn-thesis runs on solar energy, which is used to combine carbondioxideandwater into the sugarcalledglucose. Ithappens inthegreen-pigmentedchloroplastsfoundintheparenchymacellsofleaves(Figure4.1).

Thedurationandintensityofsunshine;thequalityofthesoil;andsuchenvironmentalfactorsastemperature,annualrainfall,humidity,andwindareallvariablesthataffectplantgrowth.Asyoumayhavenoticed,noteveryonerequiresthesameamountoffoodorwater.Also,someofusactuallylikecoldweather,whereasothersprefer theheat.The specific cultural requirementsofaplantinavegetablegardenaredifferentfromthoseofaplantinthewildflowermeadow,asarethosethatevolvedinalpineversustropicalversusdesertenvironments.Culturalrequirementsforsunshine,soilquality,water,andclimatearedescribedbelow.

SUNSHINEPlantshavespecificrequirementsforlightintensity,quality,andnightlength.Lightintensityreferstothestrengthofthesunlight.

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CulturalRequirements

49cultural requirements

Theoptimumintensityforplantgrowthisthatatwhichtheplantismostproficientatphotosynthesis.Higherthanoptimumlightintensitycandamagechloroplasts,whereaslowerlevelsdonotyield enough energy for photosynthesis. Shade cloth is oftenusedtoprotectsensitiveseedlingsandplantsfromstrongsunbypartiallyblockinglightandreducingtheintensity.

Figure 4.1 A plant cell consists of numerous specialized organelles. Photosynthesis occurs within the chloroplast. Other organelles include ribosomes, mitochondrion, smooth and rough endoplasmic reticulum, and the nucleus, which contains the plant cell’s DNA.

50 Horticulture

Light quality is based on the wavelengths of visible light,whichrangesfromviolet(theshortestwavelength)tored(thelongest),withall thecolorsof therainbowinbetween.Belowvioletthereistheultravioletrange,orUVlight.Aboveredthereisthefarredandinfrared.Photosyntheticpigmentshaveevolvedtointeractwithlightatwavelengthsofblueandred.Theshorterblue wavelengths provide greater energy. Far-red light causeslong, thin stemsandalso triggers the transfer fromvegetativegrowthtoflowering.Placementinthegardenaffectsthequalityofsunlight thatreaches theplant,assunlightcoming inatanangleclosertothehorizoncontainslesshigh-energybluelightthansunlightarrivingbyashorteroverheadpath.

Floweringinangiospermsistriggeredbynightlength.Photo-

periodisatermthatdescribestherelativenumbersofhoursofdaylightanddarkness.Nightbeginswithfar-redlightatduskandendswithfar-redlightatdawnandthesewavelengthsareinvolvedintheplant’sabilitytokeeptrackofthelengthofthenight.Someplantshavespecificrequirementsastohowlongtheperiodofdarknessmustlastinordertotriggerflowering.Itiscalledthecriticalnightlengthanditappearstobemeasuredbyapigmentfoundinleaves.Thoseplantsthathaveevolvedtobloomwhenthedaysarelongandthenightsareshorter(asinthelatespringandearlysummer)arecalledlongday/shortnightplants.Manyannualplantsbelongtothisgroup.Somewaitforshorterdayswithlongernights,likechrysanthemums,whichcanbloominthelatefallorevenwinter;thesearetheshort day/long night plants. Some plants, such as roses andgeraniums, are not controlled by the photoperiod and areconsidereddayneutral.Inthiscase,floweringiscontrolledbyotherfactors.

Naturaldaylightranges from8hoursatwintersolstice to14 hours at summer solstice. Ancient calendars marked thesolstices with physical structures. If you know when solsticeis,youknowwhentoplantvegetablestoensureharvestbefore


wintersetsin.Knowledgeofphotoperiodrequirementsisalsorequiredtodesignflowergardensthatwillbeinconstantbloomfromthespringthroughfall.Photoperiodcanbemanipulatedbyusinginfraredlight,whichisastrategyusedtoinduceflow-ering in commercial greenhouses. This will be described inChapter6.

Lightintensityandlightqualityareusedtoseparateplantsintogroupsthatrequirefullsun,partsun,partshadeorshade.Full-sun plants like a full day of high-quality light, part-sunplants require 5 to 6 hours of high-quality light, part-shadeplantsneedtogetfilteredlightallday,andshadeplantsrequirefullprotectionfromstrongsunallday.Thelightrequirementsforgrowthareincludedinseedcatalogsandontheseedpacket,aswellasonthetagthataccompaniesaplantforsaleinagardencenter.Thebloomtimeisalsoprovidedandmaybereportedasamonthorseasonorintermsofthephotoperiod.

SOILSoilsareoftendescribedbytheirpredominantminerals,suchassand,silt,orclay.Waterdrainsquicklyfromsandysoils;theyalsotendtobelowinnutrients.Claysoilsarehigherinnutrientsbutdonotdrainwellandcanbequitesticky.Soilsthathaveabal-ancedmixofsand,silt,andclayparticlesarecalledloams.Whenaloamsoilismixedwith3%–5%organicmatter,ithastheidealtextureforcultivationofagardenbecauseitprovidesadequatedrainageandnutrients.Soilswithlessthan1%organicmatterarenotveryfertile.Soilsthatareinthebestconditionforgrowingplantsaresaidtohavegoodtilth.Themixofmineralsinthesoilisreferredtoasthetexture andcanbedeterminedbysendingasampletoasoiltestinglaboratory.Soilstructurealsoaffectstilth.Ifasoilhasbeencompactedduetoheavyequipment,itwillbemoredifficultforplantrootstospread.

Natural soils are evolving, dynamic entities that consist ofminerals plus live microbes and decomposed organic matter.

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Organic matter is the result of decomposed plant, insect, andanimal matter plus the microbes that decompose it. Organicmatterhasbeendecomposedbeyondrecognitionoftheorigi-nalmaterial.Itisblackandcrumblyandhastheabilitytoholdlargeamountsofwaterandnutrients.Itisoftencalledhumusorcompost.TheprocessofcreatingcompostiscalledcompostingandisdescribedinChapter6.

If the soil has an abundance of clay, compost is added inordertoimprovethetilth.Addingsandtoclaysoilisnotrecom-mended,asthisproducesamaterialsimilartocement,whichasyoucanwellimagineisnotveryconducivetogrowingplants.Likewise,ifthesoilissiltyorsandytheadditionofcompostwillalso improve the tilth. However, many wildflowers and someculinary herbs prefer to grow in nutrient-poor, sandy soil sohowyouamendyour soildependsupon the soilyouhave tostartwithaswellaswhatyouwanttogrowinit.

Thereare17nutrientsthatplantsrequireinordertogrow.Theyaresuppliedbytheair,water,andsoil.Nutrientsareele-mentsusedbygrowingplantcellstosynthesizemorecellsandtohelpfuelphysiologicalprocesses.Theseelementsarecycledthrough theenvironment inaprocesscalledbiogeochemistry.Biogeochemical transformations of elements are mediated bymicrobes that may derive energy for growth and/or nutrientsfromthetransformationreactions.

Somenutrientsareconsideredmacronutrientsbecausetheyarerequiredinrelativelylargeconcentrations.Hydrogencomesfromwater;potassiumandphosphorous comefromthesoil;andcarbon,oxygen,andnitrogencomefromtheair.Sulfur,magne-sium,andcalciumarerequiredinlowerconcentrationsandalsocomefromthesoil.Othersoil-derivednutrientsthatarerequiredinevenlowerconcentrationsarecalledmicronutrientsortraceelementsandincludechlorine,iron,manganese,boron,copper,zinc,molybdenum,andcobalt.Ifanyoneofthesenutrientsisnotpresentintherequiredamount,growthoftheplantwillbe


inhibited.ThisisknownasLiebeg’sLawoftheMinimum.Toomuchofagoodthingisnotgoodinthiscase,asmicronutrientscanbecometoxictoplantswhenappliedinexcessiveamounts.Silica, a major component of sand, is also believed to be animportantmineralforplantgrowth.

Hydrogenisthemostcommonelementandisalsoanimpor-tantmacronutrient.Itisacomponentofwaterthatisfoundinsoilpores.Whenwatermolecules(H2O)split,astheyoftendo,theygeneratepositivelychargedhydrogenions(H+)andnega-tively charged hydroxy radicals (OH-). A pH meter measuresthenumberofhydrogenionsinasaturatedsoilandreturnsthevalueasanegativelogfunctionthatrangesfrom0to14.Ifthereareanequalnumberofhydrogenionsandhydroxyradicals,thepHisneutralandhasavalueof7.ApHoflessthan7isacidic;thelowerthenumber,themoreacidic itis.IfthepHisgreaterthan7thesoilissaidtobealkaline;thehigherthenumber,thegreaterthealkalinity.

MostcultivatedplantspreferasoilwithapHbetween6.5and6.8althoughafewtenthsofauniteitherwayisusuallytolerable.ThereasonforthishastodowiththeeffectofpHontheavail-abilityofnutrients.WhenthesoilpHisinthisrange,allofthenutrientsaresolubleandtheplantcanaccessthemthroughitsroots.WhenthepHismorealkalineormoreacidic,someofthenutrientswillforminsolublecompoundsthattheplantcannotaccesseventhoughtheyarepresentinthesoil.

Minerals such as calcium, magnesium, potassium, andsodium contribute to alkalinity and are called soluble salts.Theymaybeleachedoutofasoilthathasformedinhot,humidconditionswithhighannualrainfall(tropical,subtropical).ThesoilbecomesveryacidicandmayhaveproblemswithaluminumtoxicitybecausealuminumchangestoasolubleformatlowpHandtheplantscantakeitupthroughtheroots.

Solublesaltstendtoaccumulateinaridandsemiaridregionsthatareheavilyirrigated—especiallyinpoorlydrainedclaysoils

54 Horticulture

(Figure 4.2). Water evaporates quickly in these environmentsandthesaltsbecomeconcentratedintheupperlayersofthesoil.Thesesoilsarenotgoodforgrowingagardenandmaybecomehometomicrobialcommunitiesandplantsthatareadaptedtothe high salt concentration. Soils that have accumulated veryhigh concentrations of some salts (such as sodium) are verydifficulttobringintogoodtilth.Someplantbreedersarework-ingonthecreationofhybridcropsthatcanwithstandhighsaltconcentrations.

SoilpHcanbe increasedbyadding lime,which iscrushedlimestoneminedfromquarriesandcontainscalciumcarbonate.Sometimesitismixedwithmagnesiumandcalledgypsum.Theadditionofwoodashes,whicharehighinpotassium,alsoraises

Figure 4.2 The excessive use of fertilizers and irrigation in arid regions can cause overly alkaline soil. The alkalized soil forms a white crust of accumulated salts on the surface of the fields, which is toxic to most plants and detrimental to the land.


thepHofthesoil.Thisneedstobedonecarefully,severalmonthspriortoplantingtoallowthechemicalreactionstotakeplace.ToomuchcalciumorpotassiumcanelevatethepHbeyondwhatistolerabletogardenplants,anditmaytakeyearsforthepHtoloweragaintoasuitablerange.

SulfurlowersthepHofthesoil.OrganicamendmentssuchaspineneedlesandpeatmossalsolowerthepH.TheamounttousedependsuponthepHofyoursoil,thesizeoftheareayouneedtocover,andwhatyouplantogrow.Someplantssuchasblueber-riesandazaleaspreferasoilpHof6.0,moreacidicthanformostgardenplants.SoiltestresultscanindicatetheappropriaterateofapplicationofmaterialstoalterthepHofyoursoilforthepar-ticularplantsyouintendtogrow.Soiltestresultscanalsoindicatewhetheryouneedtoaddnutrientsandinwhatamounts.

If your compost and mineral soil do not supply enoughnutrients,youmayneedtosupplementwithfertilizer.Therearemanyfertilizersonthemarket.Organicandchemicalfertilizersareformulatedtosupplyamixofthethreenutrientsrequiredin abundance, which are nitrogen (N), phosphorous (P) andpotassium(K).TheamountoffertilizerisshownonthelabelasaratioofN-P-K.Somefertilizersareformulatedtosupplythemicronutrientsas traceminerals.Chemicalnitrogenfertilizersaregeneratedbytheconversionofnitrogengasintheairtoasoluble powdered form. This process requires energy becausethegaseousnitrogenbondsaredifficulttosplit.Rockphosphateisasubstanceminedfromtheground;largesuppliesarefoundinFlorida.Rockphosphatesupplieshighphosphorousandalsoaddscalcium.Greensandisfromancientseabeddepositsandisasourceofpotassiumandmanytraceminerals.Seaweedisalsohighinpotassium.

Organicfertilizerssuchasbloodmealandfishmealalsosup-ply high nitrogen. They come from slaughterhouses and pro-cessingplants.Ifyouprefernottouseanimalproducts,legumessuchassoybeanmealandalfalfamealcanbeusedasanitrogen

56 Horticulture

fertilizer.Manygrowersplantalfalfatoincreasethenitrogeninthesoil.Homegardenersoftenplantpeasorbeans,whicharealsolegumes.

Plantshavedifferentrequirementsfornutrientsatdifferentstagesofgrowth.Nitrogenpromotesvegetativegrowthandtoomuchmayresultinpoorflowerandfruitformation.Phospho-rousstimulatesrootgrowthandflowerproductionandisuse-fultoaddtoanewtransplantandwhenplantsbegintoflower.Potassiumisrequiredinthetransportofnutrientsandalsoisinvolvedin turgor pressureandtranspiration.

WATERThewaterfoundintheporesofthesoiliscalledthesoilsolutionandcarriesdissolvednutrientsaswellasmicrobiallife.Waterisnecessarytotransfersolublenutrientstoallpartsoftheplantandmustbepresentinsufficientquantitiesfortheelongationofplantcellsthatcontributetogrowth.Inwaterloggedsoils,watermoleculesdisplacethesoilairthatcontainsoxygen.Thiscauseslowerrespirationratesintherootsandcanactuallydecrease theabilityoftheplanttotakeupwaterfromthesoil,whichcausestheplanttowilt.

Rainwater is slightly acidicbecauseof the carbondioxidenaturally present in the atmosphere and may become evenmore acidic as a result of pollution. Rain is also a transportvehicleformicrobesthataresweptintotheatmosphere.Ifthereisinsufficientrainfallforhealthyplants,asupplementalsourceis required. Commercial growers may have access to surfacewater,suchaspondsandriverswithirrigationditchesusedtodivertwatertothecrops.Theymayalsouseasprinklersystem.Alternatively, wells are often used to supply irrigation waterand are preferred because the water is less likely to transmitdisease.

Waterqualityshouldbetestedpriortoplanting.Ifthewatersupplyisfromsurfacewaterorawell,thiscanbedonebysending


awatersampletoalaboratory.YouwanttocheckforpH,mineralcontent,andsolublesalts,aswellastoxicchemicalsthatcouldinjureyourplants.Ifyouareusingmunicipaltapwatertowaterplants,you shouldask thecountyormunicipality forawaterqualityreport,whichtheyshouldprovidetoyouatnocharge.Highlevelsofchlorineorfluorideintapwatermayinjureyourplants.Ifyourwaterisnotgood,youcaninvestinequipmenttopurifyit.

Themethodusedtoirrigatewatermaydependuponclimate,thesizeofthegarden,andproximitytothewatersource.Onemethodistoirrigatefromoverheadandtheotheristoprovidewaterdirectlytotherootzone.Fertilizerissometimesapplieddissolvedintheirrigationwater;thisisreferredtoasfertigation.Thereareadvantagesanddrawbackstobothmethods.

Overhead water washes off leaves and may help deterfoliagepests,butwater canbe lost toevaporationandmaynotreachtheroots,especiallyinhot,dryweather.Overheadrinseswithorganicamendmentssuchascompostteaorkelpextracts have been reported to increase plant vigor. Pivotirrigationisanoverheadsprinklersystemthatprojectswateroutfromacentralsourceinacircularmotionmovinglikethehandsonaclock,whichresultsinacircularpatchofirrigatedlandthatlookslikebiggreencircleswhenviewedfromover-head(Figure4.3).

Whenplantsareexposedtoafrost,anearlymorningrinsewithwatertowashfrostofftheleaveswillpreventdamageaslongastheleaveshavenotyetbeenexposedtosunlight.Plantscanbeprotectedfromfrostbycoveringthemwithclothorplasticorbymovingpottedplantstoashelteredarea.Yourlocalweatherreportwillgiveyounoticeifafrostisexpectedovernight.

Water applied directly to the root zone by drip irrigationconcentrates thewaterby therootswhere theplantcanaccessit.Dripirrigationdeliverswaterthroughasoakerhose,whichisperforated.Thismethodismoreeasilyappliedinthesmallgarden

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Figure 4.3 Center pivot irrigation creates circular farms such as the ones seen above. Center pivot irrigation is a type of crop irrigation in which equipment rotates around a fixed point. Computer-controlled center pivot irrigation systems allow farmers to operate from a remote location.


thaninlargecommercialfields,whichmayhaveproblemswithclogging.Thehoseislaidonthegroundclosetothestemsofyourplantsandcanbecoveredwithmulchtoreduceevaporation.

Water that is applied too late in the day, close to dusk, orafternightfallmaycreateproblemsbecauseofconditionsthatfavorthegrowthoffungi.Manytypesoffungithriveincool,moist conditions and reproduce with spores. The spores are

Plant Water requirementsHow much water does a plant need? That depends upon the plant, the cli-mate, and the rate of transpiration. Transpiration is the passage of water as a vapor from the leaf to the atmosphere. Water molecules move from areas of higher concentration to areas of lower concentration. High temperatures, low humidity, and wind can increase the rate of transpiration because they remove water from the air. If there is less water in the air than in the plant leaf, water will move from the plant into the air.

Plants that do not receive adequate water intake through the roots dur-ing times of increased transpiration may wilt, and if the conditions persist, they will die. The amount of water required varies among species that have evolved in climates with different amounts of rainfall. Plants that are native to arid and semiarid regions have modified leaves and stems that conserve water and reduce transpiration. These plants are sometimes referred to as drought tolerant or xeric.

Plants that are native to tropical regions with warm, moist air tend to have broad leaves that shed water and may transpire at a higher rate than xeric plants when exposed to hot, dry weather. High transpiration combined with evaporation dries out the soil. Plant water requirements are often listed as low, moderate, or high, with xeric plants at the low end and tropical plants at the high end. Plants with shallow lateral roots are usually not drought tolerant and require more frequent water than plants with deep taproots, which will do well even if the soil dries out between watering.

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transportedinwater.Itisimportanttoavoidworkinginawetgarden,asthiscanspreadmicrobialdiseasesthatareinwaterdroplets.Thesporescanbecomeattachedtoyourshoes,gloves,ortoolsandcauseyoutoinfectotherplants.Itisnotagoodideatotransfergardentoolsfromoneplacetoanotherunlesstheyaresterilizedbetweenuses,asresidueleftontoolscanspreadmicrobial diseases. Wet soil can also be easily compacted byfootstepsorheavymachinery,whichmakesitharderforplantstogrow.

CLIMATETheclimateof aparticular region isbasedonannual averagehigh and low temperatures, annual rainfall, and the numberof frost-free days. Wind and altitude are modifiers. Linnaeussaidthataltitudeismoreinaccordancewiththehabitationofplantsthanlatitudeorlongitude.Thisisbackedupbyresearchthatfoundthatplantsgrowinginalpineregionsaresimilarindifferentpartsoftheworld,whereasplantsgrowingatthesamelongitudeorlatitudeareoftendifferent.

TheUSDAhasgeneratedclimatemapsthatdividethecoun-try into zones based on climate. The United States NationalArboretumWeb site listed in theFurtherReading sectionhasan interactive USDA Plant Hardiness Zone Map that you canaccess to determine the zone for your region. It also providesinformationonhowtochooseperennialplantsthatwillsurvivethewinterinyourarea.

SUMMARYThischapterdescribedhowplantphysiologicalprocessessuchas photosynthesis, respiration, and transpiration are tied to aplant’sculturalrequirements.Sunshine,soil,andwaterprovidethe plant with nutrients and energy for growth. Plants differin termsof thequalityandquantityof sun,water, andnutri-ents they require, and also in their preferred soil texture. The


horticulturist’sjobistoprovideplantswiththehighestqualitylight,water,andsoilpossibleinaccordancewiththeirindividualneeds.Growersmustbeawareoftheculturalrequirementsofeachoftheplantsinthegarden.Thenextchapterpresentstheinteractionsbetweenplantsandotherorganismsandhowtheymaybebeneficialordetrimentaltothegarden.

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EcologyandPestManagement

Nature never deceives us; it is always we who deceive ourselves.

--Jean Jacques Rousseau (1712–1778)Swiss philosopher

Let’s suppose that you have done all your homework and arefamiliarwiththeculturalrequirementsofyourfavoriteplants.You have started a garden and your plants are growing great.Thenonemorning,aftersixweeksofhardwork,yougotowateryourvegetablesandalltheleavesaregone.Whatifitwasacom-mercialcropandnowyouhavenothingtosell?Theprotectionofplants fromhungrypests isanage-oldproblem.Integratedpest management (IPM) is a decision-making process that isusedtomanageorganismsthatareharmfultothegardenandisbasedonafundamentalknowledgeofecology.Itappliesanintegrated approach of chemical, biological, mechanical, andculturalcontrols.

Plants interact with insects, animals, microbes, and otherplants.Someinsects,animals,andmicrobesarebeneficialtothegarden and others are destructive. Nonbiological factors suchas climate and soil conditions affect the ecological balance ofthe garden. For example, an unusually cold, wet summer canpromotefungalinfectionsinplants.Alternatively,dryanddustyconditions may contribute to outbreaks of destructive plant-eating mites. This chapter introduces some of the beneficialandharmfulaspectsoftheinteractionsthatmayoccurbetweenplants and other organisms in either the rhizosphere (belowground)orthephyllosphere(aboveground).

THERHIZOSPHERETherhizosphere is thearea inthesoilaroundtheplantroots.Itconsistsofsoil,insects,microbes,androots.Somesoilfauna,suchasspidersandtheirrelatives,themites,arenottrueinsectsandarecalledarachnids.Theyhaveeightlegs.Spidersdonoteatplants;theyeatinsectsthathurtthegarden.Othercreatures,suchasslugsandsnails,arealsofoundinthesoilandfeedonplants.Microbesareorganismsthataretoosmalltobeviewedwithoutamicroscopeandincludebacteria,viruses,fungi,protists,algae,andnematodes.

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65Ecology and Pest Management

Somesoilmicrobesareopportunisticpathogens.Theydonotaffecthealthyplants,butifaplantisweakenedbyenvironmentalconditions,themicrobewillentertheplantandcauseinfection.Beneficialsoilmicrobesmakenutrientsavailabletoplantsandinexchangegetcarbohydratesfromtheplants.Beneficialrhizo-spheremicrobesarealsoresponsibleforthegenerationofcom-postfromanimalandplantmatter.Earthwormsarealsohelpfulin the composting process and in the recycling of nutrients(Figure5.1).Wormsshouldnotbeintroducedintoecosystemswheretheyarenotnaturallyfound,however,becausetheycan

Figure 5.1 Earthworms are an important component to composting. In vermicomposting, or worm composting, red earthworms are used to consume and digest organic matter in order to produce castings, an odor-free soil additive.

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causeextensivedamagetotheorganiclayerinforestsandreducethehabitatfornativecreatures.

Composting of green plants directly in the soil is knownas greenmanuring.Greenmanures areusually supplied fromyoungweedsthathavebeenmechanicallyremovedwitha hoe

andturnedbackintothesoiltodecompose.Somegrowersplantacold-tolerantcerealorlegumecropthatgrowsoverthewinterandthenturn it into thesoil in thespring.Thesoilmicrobesbreakdowntheplantandrecyclethenutrientsintothesoil.

Thenutrientthatismostoftendeficientinthesoilisnitro-gen. Soil microbes that belong to the genus Rhizobium formnodulesontherootsoflegumesandconvertnitrogenfromtheatmosphere into a form that becomes soluble in the soil andavailable for plant uptake. Free-living nitrogen-fixing bacteriasuchasAzospirillumandCyanobacteria arealsofoundnaturallyinthesoil.

Mycorrhizal fungi form long hyphal filaments that stretchintothesoilinsearchofnutrients;theyalsoformassociationswithplantroots.Thefungibringnutrientssuchasphosphorousto theplant inexchange for carbohydratesandmayalsopro-tect the plant from fungal pathogens.Additionally, the hyphahelpstobindthesoilparticlestogetherandgivethesoilgoodtilth.Manyplantsformsymbioticassociationswithmycorrhizalfungi.Plantsthatarenormallyfoundinassociationwithmycor-rhizalfungiwillnotthriveiftheydonotformtheassociation.It may take years to establish the associations, which are veryimportantinforestedandnaturalecosystems.Wildflowersoftendieifyoutrytodigthemupinthewildandplanttheminyourgarden,becausetheirsymbioticmychorrhizalfungidonotsur-vivethetrip.

Somesoilbacteria,suchasStreptomyces,produceantibioticsthatkillothermicrobes.Streptomycesalsoproduceasubstancecalledgeosminthatisresponsiblefortheearthysmellofgardensoil and ripened compost. Bacteria from the genera Bacillus


and Pseudomonas are used to kill fungal pathogens. They areaddedtoseedsor sterilizedpottingmediaandarelabeledandtreatedasfungicides.Theseorganismsarenaturallypresentinfertilesoilandinproperlyagedcompost,sothereshouldbenoneedtopurchasethemifyouaddhigh-qualitycomposttoyourgarden.

Fungal and viral diseases can be spread by water dropletsthatbounceoff thesoiland landon leaves.Theuseofplasticmulchforplantsthataresusceptibletoviraldiseaseshasgivengoodresults.Themulchcreatesabarrierbetweenthesoilandthe leaves. Many other types of mulch, such as cedar or pinebark(whichsmellslikethetrees),areavailable.Theyareyelloworreddishincolor.Cocoamulchsmellslikechocolateandhasadarkbrowncolor.Gravelisalsosometimesused,especiallywithdrought-tolerantplants.Strawandhayareverypopularandcanbeeasilypickedupandmovedwhenneeded,althoughyouhavetobecarefulthatthehaydoesnotcontainweedseeds.

Mulchshouldnotbeplacedtooclosetothestem,asoverlymoistconditionsmayleadtofungalinfections.Mulchisusedtolessentemperaturefluctuationsandtoconservewaterinthesoilandpreventerosion.Temperatureaffectsplantsatallstagesofgrowth.Thetemperatureofthesurfaceofthesoil,whereplantgrowthoccurs,mayfluctuatewidelyoverdailyandannual(sea-son-to-season)intervals.

Croprotationsalsohelpbecausediseaseorganismscansur-vivethewinterinthesoil.Manydisease-causingmicrobesandinsectsarespecificaboutwhichplantstheywillinfect.Ifnohostplantsareavailableforafewyears,thepathogenpopulationwilldiebackfromlackofahost.Cropsthatgrowinthesameplaceyearafteryearcancauseanincreaseintheinsectpestpopulationinthesoil.Thisiswhygrowerswhopracticemonocroppingoftenuse largequantitiesof insecticides.For example, conventionalcommercialstrawberrygrowersusedtoroutinelyfumigatethesoilwithmethylbromidetokilldiseasemicrobesaswellasweeds.

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ThissubstancehasbeenrecentlybannedbytheEPA,however,becauseitistoxictohumansanddepletesozone.Italsokillsthebeneficialorganismsinthesoil.

Weedsareplantsthatgrowinaplacewhereyoudonotwantthemtobe,suchasinavegetablegardenorinthemiddleofalawn.ManyweedsareescapedgardenplantsfromEuropeanset-tlersthatarenolongerinfashionorforeigngrassesthathitcheda ride in grain shipments.Weeds compete with garden plantsfornutrientsandwaterandmaycauseovercrowdingandleadtoconditionsthatspreaddisease(Figure5.2).

Weedscanbepulledbyhandorscrapedoffthesurfacewithahoe.Hoeshaveasharpedgethatisusedtoremovetheweedjustbelowthesurfaceofthesoil.Anyweededplantsthatarenot

Figure 5.2 A weed called giant foxtail grows between rows of corn on the right-hand side of this photograph. The corn on the left has been treated with an herbicide that prevents foxtail growth. Weeds compete with crops for nutrients and water, and they spread diseases.


ediblecaneitherbeturnedbackintothesoilasgreenmanureorputintoacompostheap.Plantsreleasecompoundsfromtheirrootsintothesoil.Someoftheseareweakacidsthathelptoreleasenutrientsfromthesoil.Plantsalsocanreleaseallelochemicalsthataffectotherplants.Someweeds,suchastamariskandknapweed,producechemicalsthatpreventthegrowthofotherplants.

Herbicidesarechemicalsused tokillweedsandarewidelyappliedbybothcommercialgrowersandhomegardeners,espe-ciallyonlawns.Sometargetthebroadleafdicotplantsbutallowthemonocotgrasses tocontinue togrow,whereasothersmaytargetthemonocotgrasses. Misuseofcommonlyusedherbi-cidescanresultincontaminationofwatersuppliesandmaybetoxictohumans.Theyarenotusedinorganichorticulture,asmechanicalmethodsofweedremovalareeffectiveandtheweedsareasourceofcompostmaterial.Weedscanbepreventedbytheuseofsmothercrops,whichareplantedinbetweenrowsorinotherplaceswhereweedsmightgrow.

THEPHYLLOSPHEREPhyllosphereisatermusedtorefertotheenvironmentintheareasoftheabovegroundportionsofaplant,especiallytheleaves.Itattractsmanyinsects.Thestudyofinsectsiscalledentomologyandahorticulturistmustlearntorecognizethebeneficialandharmful insects in a garden. Insect pollinators are beneficial.Insectsthateatplantpartsaredestructive.Commondestructiveinsectsaremealybugs,aphids,whiteflies,thrips,caterpillars,andgrasshoppers.Plantvirusesareoftenspreadfromplanttoplantbyaphidsandthrips,aswellasmealybugsandsomeleafhoppers,soyouneedtowatchforsignsofviralinfectionsinplantsthathavebeeninfestedwiththeseinsects.

Dailywalksthroughthegarden,greenhouse,orcommercialfieldwillalertyoutopotentialinsectinfestationsbeforetheygetoutofhand.Thisisoneoftheresponsibilitiesofthegreenhouseor farm manager. If plants become heavily infested, physical

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composting: How to Make Black GoldCompost, the black crumbly material that remains after decomposition of plant residues and animal manures, is worth its weight in gold to the organic or sustainable grower, but it must be of good quality. Compost heaps can be made directly on the ground or in containers. A source of microbial inoculation, such as soil or commercially available compost starter, is also required. A proper mix of carbon and nitrogen in the starting materials is very important. Straw and dried leaves are high in carbon and are often combined in layers with grass clippings or kitchen scraps, which are high in nitrogen. Straw also helps to keep air in the pile, which encourages aerobic decomposition and prevents the formation of noxious gases. Growers may also add fresh animal manure or fish scraps to the compost pile as a source of nitrogen. Fresh manure is not appropriate for direct application to the garden, as it is too strong and may burn plant roots or spread disease-causing microbes such as E. coli. Manure sources should be investigated, as some farmers give their animals high quantities of antibiotics that can inhibit microbial decomposition.

The composting process takes about six months but is sensitive to cold temperatures. A correctly built compost pile heats up to more than 60ºC. This high heat kills pathogens and weed seeds while special microbes adapted to the high temperature continue the decomposition process. The pile should be turned regularly to rotate freshly added materials into the center of the pile and keep it aerated. After the temperature stabilizes and cools, the compost should ripen prior to addition to the garden. Municipal compost piles may include sewage sludge, the residue from sewage treat-ment facilities, which contains concentrated toxic heavy metals, such as cadmium, mercury, and lead. There are strict EPA regulations with regard to how much composted sewage sludge can be applied to the soil. Compost made with sludge should be avoided by home gardeners.


methodsmaybeusedtoremovetheinsectpest.Thesemethodscanincludetheapplicationofwaterorshakingtheplantoveracontainertocatchtheinsectsastheyfall.Ifitisalocalizedinfes-tationofannualplants,theaffectedplantsareremovedfromthegarden.Iftheplantsareperennial,otheroptionstoridtheplantsofthepestmaybetriedbeforeremoval.Textsonorganicgarden-ingcanbeconsultedforadviceonaparticularproblem.

Predatoryinsectsandspidersthatfeedondestructiveinsectsarebeneficialtothegarden(Figure5.3).Ladybeetles(commonlycalled ladybugs), parasitic wasps, spiders, lacewings, syrphideflies,damselbugs,assassinbugs,andminutepiratebugsareallbeneficials.Beneficialinsectscanbeencouragedtoliveandeatinthegardenifthereisahighdiversityofplantsandtheuseof

Figure 5.3 Lady beetles, also known as ladybugs, feed on aphids, which are a common garden pest.

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insecticidesisavoided—manyinsecticidesdonotdiscriminatebetweentheharmfulandbeneficialinsects.

Somespeciesofbeneficialinsectsmaybepurchasedforinten-tionalreleaseintoafieldorgreenhouse.Thisisknownasbiologi-calcontrolandisarelativelynewmethod.Microbescanalsobepurchasedforuseinbiologicalcontrol.Bacillus thuringiensis(Bt)isacommonlyusedmicrobialbiologicalcontrol.Experimentsareunderwaytodeterminehoweffectivetheintentionalreleaseofinsectsandmicrobesareforcommercialapplications.Othercreaturessuchasbirds,toads,reptiles,bats,snakes,androdentsalsoeatharmfulinsects.

Trapcropsareplants thatarenot intended forharvestbutsupplyhabitat for insectsandareplantedalongtheperimeterofagarden.InthefoothillsofnorthernColorado,thewildsun-flowerplantsandnativeyuccaaregoodexamplesoftrapcrops.Trapcropscanprovideabreedinggroundforbeneficialinsectsthatfeedonpests.Thisensuresahighpopulationofbeneficialsavailabletoprotectyourcropduringthegrowingseason.

Companioncropssometimesworkbecausesomeplantspro-ducechemicalsthatareadeterrenttotheinsectpestofthecropyouplantnexttoit.Thescentofthecompanionplantmayover-whelmthescentofthecropthattheinsectisattractedtosuchthattheinsectisunabletofinditsfoodsource.Otherscentsmaybeunpleasantenoughthattheinsectstaysawayfromthearea.Forexample,Frenchmarigoldsandbasilemitascentthatdetersmanyinsectpestsandareoftenplantedamongvegetableplantsinthegardenascompanions.

Staggeredplanting is thestrategyofplantingacropearlierorlaterintheseasonthanusualtoconfoundtheinsectpestthatisexpectingtofinditataparticulartime.Thisworksforcropsthataredayneutralanddonotrelyonthedaylengthtoinitiateflowering.Tomatoesareoneexample.

Commercialgrowersmayfindthatinsecticidesarenecessarytosaveacropindistress,butitisimportanttoidentifytheunder-


lyingcauseof the infestationand try tocorrect it.Sometimesthemethodsused,suchasmonocroppingandamendmentsthatreducethetilthofthesoil,arethecruxoftheproblem.Insecti-cidesmayrequirethatyouobtainapesticidelicensebeforeyoucanapplythem.Sincetheyaretoxic,theyrequireasafeplaceforstorageandmayrequirespecialdisposalmethods.Theymayalsorequirespecialequipmenttoapply.Manyinsecticidespersistinthesoilorcontaminatewatersupplies.Also,insecticidescanbeexpensive.

ANIMALPESTSAnimalssuchasrabbits,deer,andbirdsmayeatflowers,leaves,and fruits, andgophers eatbulbs—allofwhichcan leaveyouangryandfrustrated.Animalsareparticularlyfondofplantsthatarewellfertilizedandwateredfrequently,becausetheyaremoretastyandnutritiousthanthewildplants.Thereareseveralwaysthatgardenershavehandledthisproblem.

The first way is to exclude the animals from your garden.Thisismosteffectivelydonewithgardenwallsorfences.Deerare capableof jumpingquitehigh, so the structurehas tobeabout8feet(2.4meters)tall.Nettingwithameshsmallenoughtokeepoutbirdscanbeplacedover the topsofplantswhenfruitsbegintoripen.Itismoredifficulttoexcludegopherswiththismethod,althoughyoucouldplantyourbulbsincontain-ersthatareburiedinthegroundtopreventthegophersfromreachingthem.

Asecondwaytoexcludeanimalpests is to trickthemintothinkingthatapredatorisnear.Fox,coyote,andbig-caturineobtainedfromzooshasbeenreportedtodeterrabbitsanddeer,who fear the presence of these predators. Scarecrows, shinyreflectiveobjects,ribbons,statuesthatlooklikeowlsorhawks,andbitsofhosethatlooklikesnakeshavealsobeenusedtoscarebirds.Awell-behaveddog that intimidatesanimalgrazersbutthatdoesnottrampleyourgardenmayalsobeeffective.

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Athirdmethodistospraysomekindofconcoctionontheplantsthatgivesthemadisagreeabletaste.Therearemanyfor-mulasonthemarketandhomemaderecipesthatcanbetried,buttheyneedtobereappliedafteritrains.Afourthoptionusesmechanical means that are activated by motion detectors tochaseawayanimals.These includeelectric fences,alarms,andsprinklers.

Lastly,thereareplantsthatdeerandrabbitsprefertoavoid.Deerinsomeregionsmayeatplantsthattheywillnottouchinotherareas.Thismaybereflectiveofthesoilanditseffectontheplant,oritmaybeduetolackofmoredesirablefoodplants.Dur-ingaparticularlyseverewinter,deermayresorttoeatingplantstheynormallywouldnotgonear.

MAINTENANCETherealscienceinhorticulturecomesfromobservationsandrecordkeeping.Takingnotesondailyorweeklywalksthroughthegardenduringthegrowingseasonishighlyrecommended.These notes can include information on any observed insectdamage,nutrientdeficiencies,microbialdiseases,orweeds.Itisalsonecessarytokeeparecordofanytreatmentsthatyouapply,andtheresults.Thesenoteswillhelpyoumakedecisionsaboutchangesthatyoumayneedtomakeforthefollowingyear.

Itismostimportanttorememberthatyouremovenutrientsfrom the soil by harvesting plants and that you must returnnutrientstothesoil.Plantsthatdonotreceivesufficientnutri-entsaremorepronetoattackbyinsectsandmicrobialdiseases.Ontheotherhand,soilsthatareoverfertilizedhaveareductioninthebeneficialmicrobesthatrecyclenutrientsandhelppre-ventdisease.Regularmaintenanceandbest management practicesthatlimittheamountofchemicalfertilizershelptokeepplantshealthy.

Organicgardenersbuildupthesoilwithregularincorpora-tionofcompostandkeepthepHinarangebetween6.5and6.8


toensureplant-availablenutrients.Compostcanbesprinkledontothegardenanddoesnothavetobedugin.Youcanalsosprinklecompostonyourlawn.Whenyoumowyourlawn,youshouldallowtheclippingstostaythere.Thisreturnsnutrientsandlessenstheneedfortheadditionofnitrogenfertilizer.

Exposed soil often forms a hard, crusty surface as waterevaporates.Thenext timeyouwateror thenext time it rains,the water will run off the hard surface instead of penetratingintothesoil.Thisisdesirableinthedesert,wheredesertcrustsdevelop bacterial communities that prevent erosion and addnutrientstothesoil.Inthegarden,thecrustneedstobebrokenupandturnedintothesoil.Agardentoolcalledacultivatorhasmetalprongsthatareusedtobreakupthehardsurfaceofthesoil.Addingmulchtothetopofyourexposedsoilcanpreventthiscrustfromforming.

Manyherbaceousfloweringplantsbloomlongeriftheyaredeadheaded.When the bloom begins to wither, it is removedfrom the plant and added it to the compost heap. Decayingblooms and dead leaves are susceptible to gray rot, a fungaldiseasewithafuzzygrayappearancecausedbyBotrytis cinerea (Figure5.4).

Purchased plants have to be inspected for pests such asmealy bugs, mites, white flies, or aphids because they can betransferredtoyourgarden.Plantsthatarespindly,wilted,orhavedamagedleavesmaycarrymicrobialdiseasesandshouldnotbebought.

Plants shouldnotbecrowdedclosely together, as thispro-motesthespreadoffungaldiseasesthroughpooraircirculation.Thegardenshouldbe thinnedas it isgrowingtoallowplantsroom to spread. The recommended distances between plantsareprovidedonseedpacketsortagswithtransplants.Thinninginvolves removing weaker crop plants or weeds to allow thelarger,healthycropplantsroomtogrow.Perennialplantsmustbedividedeveryfewyears;otherwisetheywillgettoocrowded

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anddeclineinhealth.Theyaredugupeitherinthespringorfall,dependingonthecultivar,thenareseparatedandreplanted.

Climbingplantsneedtobeprovidedwithastructuretoclimb.Fruitingplantsaremorepronetodiseaseiftheyarelyinginthesoil.Cropssuchaspeas,beans,squash,andcucumberscanbetrainedtoclimblengthsofnylonstringthathavebeenattachedtoawoodenframe,oronatrellis.Cropssuchasraspberriesandgrapesneedtohavesupportstructuresaswell.Tomatoesusually

Figure 5.4 Botrytis cinerea grows on a young petunia plant. Plant dis-eases caused by Botrytis fungi commonly infect vegetables, ornamen-tals, fruits, and some field crops. It is one of the most frequent causes of infection in greenhouse plants. Spread of the disease can be controlled by the removal of the dead or dying leaves and flowers.


requirestaking,asdomanytallfloweringplants.Theweightofthefruitorflowermaycausethestemstodroop.Therefore,theyareattachedlooselytoastake.

Woody ornamental plants are pruned once a year or lessoften to remove dead branches, and sometimes live branches,tochangetheshape.Pruningisaccomplishedwithatoolcalledpruningshears,whichcomesinvarioussizestoaccommodateplantswithbranchesofdifferentdiameters.Smallsawsareusedontreelimbs.Treesandshrubscanbedamagediftheyarenotpruned correctly. Fact sheets on the maintenance of woodyplantsarereadilyavailablethroughthehorticulturalextensionservice.

SUMMARYThis chapter presented the interactions that plants have withother plants, microbes, insects, other soil fauna, and animals.Maintenanceofgoodtilthandabalancedgardenecologycangoalongwaytopreventmanypestproblems.Ifyouarerealisticaboutwhattoexpectfromyourgardenandsomewhattolerantofthecreaturesthatshareyourgardenspace,youwillderivemorepleasureandlessfrustrationfromyourefforts.Someofthechal-lengesfacedbycommercialgrowers,aswellasharvestandpost-harvestmethodsandtechniquesforgreenhouseproduction,arediscussedinthenextchapter.

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We abuse land because we regard it as a commodity belonging to us. When we see land as a community to which we belong,

we may begin to use it with love and respect.--Aldo Leopold (1887–1948)

American ecologist

Next time you eat a french fry, think about where the potato camefrom.Mostofusarecompletelydependentoncommer-cialhorticulturetosupplyuswithseeds,plants,produce,flow-ers,herbs,andalltheproductsthatarederivedfromthem.Weexpecthigh-qualityproductsatanaffordableprice.Sowhatdoyouthinkarethebiggestchallengestocommercialhorticultureandwhatcanbedoneaboutthem?Twoofthegreatestconcernsaretheaccesstogoodqualitynaturalresources:waterandsoil.Otherproblemsarethepotentialforcatastrophiccroplossduetodiseaseorbioterrorism,and internationalcompetition thatdrivesdownpricesandmakesitincreasinglydifficultforcom-mercialfarmstomakeaprofit.

Wellwaterispreferredforirrigationbecauseitisusuallyofahigherqualitythansurfacewaterfromponds,lakes,orrivers,which can contain pathogens. Excessive use of groundwaterthroughheavyirrigationcausesgeologicproblems,suchasthoseseen inCalifornia,Texas,Arizona,andsomeof thestates sur-roundingtheGulfofMexico.Oneofthebestexamplesisseenin the experience of Mexico City. The water is withdrawn bywellsfromaquifersataratethatisfasterthantherechargeoftheaquifersbyprecipitationandpercolation; if thesoilpores thatwereoncefilledwithwatercollapse,theaquifercannotberecharged,thewellsrundry,andthelandsinks.

TherateofwaterwithdrawalfromtheColoradoRiverandthecurrentdrought,combinedwithpopulationgrowthinthesunny,warmregionsoftheSouthwest,furtherendangersfresh-watersuppliesandwreakshavocontheenvironment.Commer-cialhorticulturetendstofollowthesunbecausewarmerclimatesmean longergrowingseasons,but there simply isnotenoughwatertogoaroundandthepoorColoradoRiverisdraineddrybeforeiteverreachestheocean.Additionally,heavyirrigationofsoilinsemiaridandaridregionscreatesproblemswithsalinationandpoorsoilfertilitysimilartothosethatcausedthedownfall

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81commercial Horticulture

ofancientMesopotamian,Egyptian,Greek,andRomanagricul-turalproductivity.

Asurbansprawlencroachesonagriculturalland,thereareconflicts.Thewell-drainedloamysoilsthatareperfectforgrow-ingcropsarealsoidealforbuildinghouses,anditisverytempt-ingforafarmerwhoisbarelygettingbytosellthelandtothehighest bidder. When residential neighborhoods come intocontactwith farmland, thereareconcernswithdangersasso-ciatedwithpesticidedriftanddrinkingwatercontamination.AcrosstheUnitedStates,primefarmlandisbeingturnedintohousingdevelopments.Increasedpressureforbiofuels(suchasethanol,whichismadefromcorn)maytranslateintoevenmorelandtakenawayfromfoodproduction,withacorrespondingincrease in the amount of chemical fertilizers and herbicidesapplied.

The frozen-food industry often contracts with farmers togrow specific cultivars because the plants yield fruits or veg-etablesofaconsistentsizeandqualitythatcanbereadilypro-cessedbytheirmanufacturingequipment.OneexampleistheRusset potato, the cultivar bred by Luther Burbank, which istheperfectsizeandhasthebestconsistencyformakingfrenchfries(Figure6.1).Theproblemisthatthispotatocultivarisalsopronetodisease.Heavyapplicationsofpesticidesarerequiredtoproduceacropacceptabletofactoryowners.Thisisnotinthebestinterestsofthefarmer,becauselandabusedwithheavyapplicationsofchemicalfertilizersandpesticidesbecomeslessfertile over time and can endanger the health of the farmer.Othertypesofpotatoesarediseaseresistantanddonotrequirethepesticideuse,butthefactorywantstheRussetssothefarmereitherproduces themor loses thecontract.Factory farmsareonereasonthatfarmerspracticemonocropping.

Aproblem with monocroppingisthereductioninthegene-ticdiversityofourfoodcrops. Highdiversitymeansthatacrop

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Figure 6.1 Technicians inspect Russet potatoes, the potato of choice for french fry processors.


hasmanydifferent varieties.Someofthesemayhavetraits forresistancetoaparticulardisease.Thelowerthediversityofourfoodcrops,themoresusceptibletheyaretooutbreaksofnaturaldiseases or bioterrorism. Low crop diversity has led to cata-strophic failureasaresultofdisease,becauseall theplantsaresusceptibletothesame pathogens.Thecornblightof1970wipedoutmostofthenation’scorncropbecausegrowersallplantedthesamevariety,whichcouldnotresistthismicrobialinfection.Seed gene banksstoregeneticdiversityforbreedingnewhybridsofimportantfoodcrops,butunlessdiversecropsareplantedinthefield,asinglediseasecanwipeoutentireharvests.

Allofthissoundsquitedreadful,butmanycommercialgrow-ers are implementing sustainable methods to overcome theseproblemsandlegislaturesacrossthecountryaretakingstepstoconservefarmlandandgoodfreshwater.Thereisalongwaytogo.Consumerdemandfororganicallygrownproducehelpstoputpressureonthefoodprocessingindustry,whichinturnmayhelpfarmerswhowanttoplantmorediversecropsandreducepesticideuse.

GREENHOUSECROPSOnewaytodecreasetheneedforsoilandwaterresourcesiswithgreenhouseproduction(Figure6.2),althoughnotallcropsmaybesuitableforthis.Greenhousecropssuchastomatoes,cucum-bers, lettuce, peppers, herbs, and strawberries are grown withhydroponics.Technically, the termhydroponicdescribesplantsgrowninwaterthathasbeenamendedwithsolublenutrients,butnowitisalsooftenusedtodescribeplantsgrowninsometype of sterilized material to give the roots a place to anchor.Thesematerialscanbegravel,sand,orrockwool,whichisspunfibersfrommeltedrocksthathavebeencompressedintocubesorslabs.Thebenefitsofhydroponicversusfield-growncropsarelowerwateruse,lessdisease,fewerfertilizersrequired,lesslabor,reducedneedforpesticides,lessdamagetotheenvironment,and

84 Horticulture

Figure 6.2 Traditional greenhouse production of plants involves over-head irrigation as opposed to the method described in the text for hydro-ponics. Greenhouses allow for a controlled environment unsusceptible to harsh weather conditions, but plants are still prone to insect infesta-tions and microbial diseases and must be carefully monitored.


higheryield.Wateriskeptinaclosedsystemandrecycled.ThenutrientlevelsandpHofthewaterarecloselymonitoredandadjustedasneeded.Thewatercanbereusedformanymonths.

Another similar method is the ebb and flow system usedwith potted plants. The pots are filled with a sterilized mediacomposed of various combinations of peat moss, pine bark,vermiculite,orsand.Beneficialmicrobesthathelppreventpatho-gensfromcausingdiseaseareofteninoculatedintothepottingmedia.Organicgrowersmayusewell-ripenedcompostthathasbeensievedthroughasmallmeshscreen.Thepotsarekeptinlarge, waterproof plastic trays, which are periodically floodedwithwater.Theplantsabsorbthewaterfromthebottomofthepotbycapillaryactionintherootsandtheexcesswaterisdrainedintoareservoircontainerandrecycledformanymonths.

Hydroponicandebbandflowmethodscanbemodifiedtomeetmanyoftherequirementsfororganicorsustainablecerti-ficationandtheyarelessdegradingtotheenvironmentthancon-ventionalagricultureinthefield.However,notallgreenhousesarepesticidefree.Insectinfestationsinthegreenhousemaybemoredifficult todealwith thanoutdoors in the fieldbecausepredatory insects and other creatures that normally consumethesepestinsectscannotgetintofeed.

Plantsinfectedwithvirusesorothermicrobialinfectionsaresusceptibletoinsectinfestations,andfungalinfectionsarecom-mon.Therefore,manycommercialgreenhousesregularlysprayinsecticides. Many of these chemicals persist on greenhousebenches,onplants,andonthefloor.Commercialgreenhouseshaveadedicatedquarantineareathatisusedtoholdnewplantsforafewweekspriortotheirintroductionintothegreenhouse.Thisistoallowtimetoobserveandremoveanypeststhatmayhavehitchedaride,beforetheygetintothegreenhouse.

Stickycardscoloredblueoryellowareoftenusedtomoni-torandtrapharmfulinsects,especiallythripsandwhiteflies,inthegreenhouse.Theinsectsareattractedtothecolorfulcardsandgetstucktothesurface.Additionally,pheromonetrapsmay

86 Horticulture

behelpful. Insectsreleasepheromonesto luremembersofthe opposite sex; these can be used to entice pests into thetraps.

Insufficientsunlightmaycauseproblemswithplantgrowthand development. Sunlight in greenhouse structures made ofglassisat89%ofunobstructedlight.Polyethylenedouble-paneplastictransmits84%.Greenhousesmustbekeptcleantotrans-mitthisamountoflight.Plasticalsotransmitslesslightwhenitisscratched.Raincleanstheoutsideofagreenhouse,buttheinsidemustberegularlymaintainedandkeptfreeofplantdebrisandstandingwater.DiseaseisspreadthroughstandingwateronthefloorsandfromfallenleavesandwitheredflowersthatmayharborBotrytismoldspores.

Plantsneedprotectionfromhigh-intensitylightduringthesummer,soshadeclothorwhitewashisusedonthewindowsto block some of the light. The greenhouse must also havean adequate ventilation system since good air circulation isrequiredtopreventdiseases.Carbondioxide,whichisrequiredforphotosynthesis,maybecomedepletedifthegreenhouseisclosed during inclement weather. Injection of carbon diox-ide into the closed greenhouse can increase photosynthesisandspeedupthetimetoharvestaslongasthereissufficientlight.Theamountofcarbondioxiderequiredtoincreaseplantgrowthisnothighenoughtocauseanyproblemstohumanswhobreathetheair.

The temperature in the greenhouse is crucial and must bewithintherangerequiredforthecrops.Heatingcostsarehigherincoolerclimates.Locationsneartheequatorhavelongergrow-ingseasonsandmorehoursofsunlight,andthushavenoneedtoheatthegreenhousesduringthewinter.Asaresult,theycanoffergreenhousecropsatalowercost.InternationalcompetitionhasbeenparticularlytoughontheAmericancut-flowerindus-trybecausethesecropscanbeefficientlytransportedoverlongdistanceswithminimaldamage.


FLORICULTURELongstemroses,thenationalflowerofAmerica,andcarnationsaretwoexamplesofcut-flowercropsgrowninthegreenhouse.Roses are grown in beds on the floor of greenhouses and theplantsproducecuttingsforabout5years.Therosesreceiveafullday of natural sunlight, and specialized lightbulbs extend thetotalamountoflightupto18hoursperday.Thisway,theplantscanbecutfourtimesayearandharvestsaretimedforChristmas,Valentine’sDay,Easter,andMother’sDay.

Floweringpottedplantsincludepoinsettias,marketedaroundthewinterholidays,andgeraniumsthatareverypopularfromMother’s Day through Memorial Day. Poinsettias may havetheir photoperiod manipulated by bursts of infrared light inordertotimethebloomfortheholidays.Greenplants—whicharesometimescalledfoliageplantsorhouseplantsandincludephilodendrons,ficus,andferns—arealsogrownforsaleinpotsorhangingbaskets.

Beddingplantsareraisedforsaletoconsumerswhoplantthemintheirgardensorwindowboxesandincludeabout50differenttypesofflowersandvegetables(Figure6.3).Thesecropsarestartedinplastictrayscalledplugs,whicharemechanicallywateredandfertilized.Theseedlingsaretransferredintotheflats,smallcon-tainers,orsmallpotsthatarefoundatthegardencenter.

HARVESTANDPOSTHARVESTCropsaregrownwithoneultimatepurposeinmind:theharvest.Harvestcanbeginshortlyafterplantingifyouconsiderthatwhenyouthinrootcropssuchascarrots,youcaneatthesmallbabycarrots.Leafygreenssuchaslettuceorspinachcanbeharvestedleafbyleafasneededforsalads.Chivesandotherherbsarealsoharvestedasneededthroughoutthegrowingseason.

Year-round harvest can be achieved with careful planning.Cropsareplantedcontinually,everythreeweeksorso,topreventalltheplantsfrommaturingatthesametime.Cold-seasoncrops

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thataregivensomeprotectionwithacoldframecanbeleftinthegroundwellintothewinterincoolerclimatesandharvestedwhenneeded.

Fruitsareharvestedastheyripen.Commerciallygrownfruitsmaybestoredincontrolledenvironmentswithahigherratioofcarbondioxidethanfoundintheairtoinhibitripening.Thesemustbespecializedroomsthatareenteredwearingprotectiveequipmentbecausetheairisnothealthytobreathe.Ethyleneisagasusedtoinduceripeninginapples,tomatoes,andbananas.Itisalsousedtoharvestcommerciallygrownpineapples,black-berries, blueberries, and cherries. Rotten apples produce highamountsofethyleneandcancauseotherfruitsthatarestored

Figure 6.3 Bedding plants are often grown in greenhouses, such as at the Plantorium in LaPorte, Colorado, pictured above.


withthemtooverripen.Therefore,itisbesttostoreapplessepa-ratelyfromotherfruits.

Crops may be harvested by hand (for example, tomatoes,whicharepronetodamage)orbyspecializedmachines(suchas bean pickers) that have been designed specifically for thatpurpose.Cropsfreshfromthefieldmaystillbewarmedfromthesunandhavewhatiscalledfieldheat. Theheatpresentintheplantcausesrapiddecayafterharvestandcanbereducedbyharvestingearlyinthedayandimmediatelystoringtheproduceinacooler.

Postharvesthandlingofthefruitorvegetablediffersforeachcrop.Somemayneed tobedriedprior to storage.Crops thathavesoilonthemshouldbewashedthoroughlypriortodrying.Perishablecrops,likeleafygreens,lastlongeriftheyarestoredinarefrigeratorwiththestemsinacontainerofwaterandaplasticbagplacedoverthetop.Harvestedproducethatisnotsoldfreshordriedmaybefrozen,canned,fermented,orpickled.Frozenfoodshavebecomemorepopular inrecentyears thancannedgoods,althoughcanning is still thepreferredmethodforpre-servingtomatoes.

SUMMARYThischaptercoveredtheproblemsassociatedwithsoilandwaterusedforcommercialhorticultureandsomeofthewaystheymaybeovercome.Greenhouseproduceandfloriculturecrops,andharvestandpostharvesthandlingofcrops,werealsointroduced.Thefollowingchapterpresentssomeguidelinesforresidentialgardendesign.

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GardenDesign

For thee the wonder-working earth puts forth sweet flowers.

--Lucretius (99 B.C.–55 B.C. )Ancient Roman poet and philosopher

Public and private gardens and parks provide us with placestorelaxandenjoyourselves.Manypeopleenjoygardeningasahobby,andresidentialgardenshavechangedover theyears ina way similar to how fashions change, since new cultivars areintroducedandothersfalloutoffavor.Althoughthedesignofagarden isamatterofpersonal taste,a fewguidelinescanbefollowed.Thesuccessofyourgardendesigndependsmainlyonhowwellyourchosenplantsfitwithyoursoilandclimate.Whatdoyouthinkareimportantfactorstoconsiderwhenchoosingplantsforthegarden?

PLANNINGYOURGARDENFirst,youneedtodetermineyourhardinesszonebyconsultingtheUnitedStatesNationalArboretumsitelistedintheFurtherReadingsection.Thiswillnarrowyourchoiceofperennialplantstothosethatcansurvivethewinterinyourarea.Plantsthatarenativetotheregionwheretheyarecultivatedarealreadyadaptedtothesoilandclimateandrequirelessworkthanexoticplants.Ifyouhaveapassionforanexoticplantthathasrequirementscompletely different from what your climate and soil have tooffer,itwillbemuchmoreofachallengetogrow.

Youcangetageneralideaofthetypesofplantsthatarenativetoyourareabydeterminingthenaturalecosystemoftheregion.Doyoulivehighinthemountains,inthedesert,intheplainsoftheMidwest,alongthecoast,inthecoldNorthorsubtropicalDeepSouth?Cultivarsfromsimilarecosystemsinotherpartsoftheworldmaythriveinyourgarden.

Next, choose the locationof thegarden.Theplacementofthegardenhastoconsidertheangleofthesun,whichdiffersinsummerandwinterandaffectslightquality.Makeadiagramoftheareayouintendtocultivateandnotethenumberofhoursofsunshineitreceives.Shadowscastfrombuildings,trees,walls,andotherstructureschangeoverthecourseofthedayandfromseasontoseason,soithelpstotakesometimetomakeobserva-

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93Garden design

tionsbeforeyoudecideonyourlocationanddesign.Determinewhetherthesitereceivesfullsun,partsun,partshade,orshade,andfurthernarrowdownyour listofplantstothosethatwillthriveunderthoselightconditions.Also,ifyouwanttoplantalawnyoumustdistinguishbetweenturfgrassesthatthriveinsunversusthosethatlikeshade.

Finally,determinethetypeofsoilinyourchosensitebysendingsamplestoalocalsoil-testinglaboratoryandtellingthemthetypesofplantsyouwouldliketogrow.TheywillrecommendwhetheryouneedtoamendyoursoilpHoraddfertilizersorcompost,andinwhatamounts.Alsomakesurethatifyourplantsrequiresupple-mentalwater,youarenearenoughtoasourcethatyoucaneasilywaterthemwhennecessary.Mostplants,includingthosethattoler-atedrought,requiresupplementalwateruntiltheyhaveestablishedastrongrootsystem—thiscouldtakemorethanayear.

Youcangetmore ideas forplants to try inyourgardenbyreadinggardenmagazines,takingtripstolocalgardencenters,orbylookingthroughseedcatalogsandtalkingtoyourneighbors.Seedcatalogsofferthegreatestselection,butifyouwantmoreimmediateresultsyouneedtopurchasebeddingplants.Youmayalso want to incorporate woody ornamentals and a lawn intoyourlandscape.Mostgardensareaworkinprogressandmaytakeyearstocomplete.

Onceyouhavealistoftheparticularplantssuitableforyoursite,youmustgroupthemtogetherinsomesortofanartisticarrangementbycolor, shape,andsizeandmakesure theyaretimedtobloomsothatthegardenhasyear-roundappeal.Usu-allysixofeachtypeoffloweringplantaregroupedtogethertogetamorevividdisplayofcolor.Thecolorandshapeofboththefoliageandflowersareconsidered.Amixofplantswithdifferentphotoperiodsbloomsatdifferent timesandprovidesa longerdisplay than plants that bloom all at once. Annuals bloomfromspring through fall andareoftenused incombinationwithperennialsthatonlybloomforamonthortwoeachseason.

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Fragrantflowersarechosentoperfumetheair.Agardenthatisusedatnightmayhaveplantswithwhiteflowersandsilverfoli-agethatreflectsthemoonlight.

Formal garden designs include geometric patterns createdwithcarefullyprunedwoodyornamentalsandplantswithcolor-fulandsweetlyscentedblossoms,andmayhaveworksofartsuchas statues or frescoes incorporated into the design. There canbefountainstocoolthetemperatureintheheatofthedayandbenchesonwhichtositandenjoythetranquilityofthegarden.Smallpondsorartificiallycreatedwatergardensarecultivatedtoproducewaterliliesandotherwater-lovingplants(Figure7.1).

Figure 7.1 Small ponds with water lilies or other aquatic plants are popular features of formal gardens. The garden above is located in Ravello, Italy.

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Landscapingmayalsoberequiredtoaddplantsbacktosoilthathasbeendisturbedbyconstructionorotherhumanactivity.Plantsthatgrowquicklyfromseedandformfibrousrootsareoftenusedtostabilizesteepbanksthatarepronetoerosion.Youcan increasewildlifehabitatwith the creationof awildflowermeadoworcreateprivacywithtrees,thickets,orhedges,whichwillalsoprovidefoodandshelterforwildlifeandactaswind-breakstoslowthewindandcreatemicroclimates(Figure7.2).

Figure 7.2 Deryl James from Trees Unlimited in Saratoga, Wyoming, stands next to a windbreak planted on a residential building site.

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Plants such as philodendrons are often used in public andprivateindoorspacestoaddvisualinterestandtopurifytheair.Inthesecases,theplantsareusuallychosenfortheirdistinctivefoliageandlowmaintenanceandareplantedindecorativecon-tainers.Theseplantsareusually tropicalplantswithattractivelargeleavesthatdonotrequirefullsun.

BEDPREPARATIONANDPLANTINGOncethegardenisdesigned,itneedstobeplantedbutthebedsmustbepreparedfirst.Therearenumerouswaystoprepareagardenbed.Mostoftheminvolvetillingthesoilwitha shovel.Soilthatisloosenedtoadepthof1foot(0.3meter)willaccom-modatemostgardenplants.Largergardenareasmaybe tilledwithagas-poweredrototiller,whichcanberentedfortheday.Thebeds shouldbenarrowenough thatyoucancomfortablyreachacrossandworkwithplants.Thelengthofthebedscanvaryaccordingtoavailablespaceandtheamountofeffortyouare able to put into the garden, but is usually no longer than50feet(15m).Pathsbetweenbedsneedtobelargeenoughtoaccommodateawheelbarroworgardencart.

Raisedbedsareoftenusedbecausetheyprovideeasieraccessto the crops and require less digging to prepare (Figure 7.3).Theymaybeenclosedwithwoodenboards,orstoneorconcreteblocks. Pressure-treated wood is avoided because it can leachtoxicchemicalsintoyoursoil.Raisedbedsareonaverageabout8inches(20.3centimeters)high.Somerootcropsmayrequireadepthof1foot(0.3m)andsomecrops,suchaslettuce,canbe6inches(15.2cm)high.Thebedscanbefilledwithhomemadecompostandsoilfromyouryard,oryoucanpurchasesoilandcompostfromanursery.

It isalsoimportanttoknowthehistoryof landusewhereyouwanttoplantyourgarden.Iftheformerownershaveusedhighamountsofpesticides, itmayaffectyourability togrowplants.Also, certain soils should not be disturbed to create a

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Figure 7.3 Raised beds can be made from wood, stone, or concrete. Stone was used for raised beds at the Villa Ruffolo in Ravello, Italy (TOP), while wood was the material of choice for raised beds in this private garden in Swanton, Vermont (BOTTOM).

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garden,astheyhaveamoreimportantpurpose,suchashabitatforrareplantsoranimalsandwetlands.Poorsoilmaybedif-ficulttobringintogoodtilth;youmayhavebettersuccesswithcontainers.

Containergrowingisanoptionthathasbecomeincreasinglypopular.Cropsgrownincontainersrequirelesspreparationandmaintenancethanthosegrowningardenbeds,andtheycanbemoved. Two additional benefits to container horticulture arefewerproblemswithmicrobialdiseasesandweeds.Containerscanbemadeofclay,plastic,wood,ormetal.Plasticholdswaterbetterthantheothermaterialsandislighter.Woodhelpskeepthesoiltemperaturefromwidefluctuations.Metalmaygetveryhot.Claydriesoutfairlyquicklyandcanbreakmoreeasilythantheothersbut isgood forusewithplants, suchascactusandsucculents, that prefer to be kept on the dry side. Containersshouldhaveholesatthebottomtoallowfordrainageortheycanbemodifiedsothattheyretainwaterawayfromtheroots,inabottomreservoirunderanabsorbentmaterial.Thesearetheso-calledself-wateringcontainersandareespeciallyusefulinaridclimates.Whenspaceisanissue,youcancreateaverticalgardenwithplantsthatliketoclimb,byplacingcontainersnearwallsorbyusingatrellis(Figure7.4).

Youcancreatemicroclimatesinyourgardentomodifyyourclimateandincreaseyouroptionsforthetypesofplantsyoucangrow.Forexample,youmaybeabletogrowcold-sensitiveplantsagainstasouth-facingwallthatholdsheatifyoucoverthemwithastrawmulchinthewinter.Plantsthataresensi-tivetocoldtemperaturescanalsobeprotectedwithplasticorglassenclosuresor rowcovers.Windbreaksareused to slowthewindbeforeitgetstothegarden.Open-weavefenceswithsomespaces,suchasalatticeorwovenbranches,breakupthewind very well. Solid structures tend to generate wind cur-rents.Livingfencescanbecreatedwithsmalltreesorhedges;

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Figure 7.4 A small lemon grove and flowers in planters create a lush garden in a small space.

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Figure 7.5 The use of a retaining wall to create level garden beds is widely used on the steep Amalfi coast of Italy, as demonstrated by this garden at the Villa Scarpariello.

101Garden design

steepslopescanbemodifiedwithterraces.Terracescreatelevelgardenbedsonsteepslopesthroughtheuseofretainingwalls(Figure7.5).

Ifyouliveinanurbanareaanddonothaveaccesstoabal-conyorrooftop,youmaybeabletojoinacommunitygardeninyourneighborhood.Communitygardensareoftencreatedinvacantlots.Youmayvolunteeryourtimetohelpcleanupthelotinexchangeforaplotinwhichtogrowyourgarden.Youmayalsotrytogrowplantsindoorsincontainerseitheronasunnywindowsillorwiththeaidofsupplementallights.Theancienthorticulturalartofbonsai createsminiaturelandscapesinsmallcontainers.

SUMMARYAgoodgardendesignconsidersthelocationofthegardenandthe amount of sunlight, the limitations of climate, soil, andavailable space, and balances them with the time and moneythatcanbedevotedtoplantingandmaintenance.Thenext,andlast,chapterprovidesinformationonthespecializedprofessionswithinthedisciplineofhorticulture.

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HorticulturalProfessions

A journey of a thousand miles must begin with a single step.--Lao-tzu (c. 604 B.C.–c. 531 B.C. )

Chinese philosopher

Some folks garden to grow good food, others grow gardens for theflowers.Somedelightinagreen,freshlycutlawnoranearlyspringbloomingorchidinasunnyliving-roomwindow.Somelikethefactthatthegardenaddsvaluetotheirrealestate.Thereareeventhosethatturntheirpassionforgardeningintoapro-fession.Therearequiteafewoptionsforthehorticulturist,asdescribedbelow.

A degree in horticulture can provide additional opportu-nities.Horticulturedegreesareofferedat land-grantcolleges(Figure8.1).Everystatehasaland-grantcollegeandtheyareusuallypartoflargestateuniversities.Land-grantcollegeswerestarted in the late1800sbyacongressionalact sponsoredbyJustin Morrill from Vermont, as public institutions to teachagriculture.Youcanfindtheland-grantcollegecampusloca-tionsonlineat theNationalAssociationofStateUniversitiesandLand-GrantCollegesWebsitelistedintheFurtherReadingsection.

Land-grantcollegesoffercoursesthatexposeyoutoallthefacetsofhorticulture.Someareasofspecialtyincludehorticul-turaltherapy,businessmanagement,floriculture,vegetablepro-duction, fruitproduction,woodyornamentals, turf, landscapearchitecture, greenhouse management, seed production, andplantbreeding.

Horticulture therapists work with patients in gardens athospitals,communitycenters,retirementhomes,andschools.Business managers can work in nurseries, greenhouses, andhorticultural supply companies. Floriculturists can work ingreenhouseorfieldproductionofcutflowersandornamentalhouseplants, as wholesale distributors, or in florist shops asflowerarrangers.Fruitandvegetableproductionoffersemploy-ment in production, management, postharvest distribution,andwholesaleandretailofplants,seeds,andproduce.

Landscapearchitectsservediverseclientsandmaydesigngardensforhomeowners,corporations,commercialsites,and

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105Horticultural Professions

publicspaces.Gardenersandlandscapemaintenancecompa-niesareemployedby the sameclientele.Turf specialistscanbeemployedbytheownersofgolfcoursesandathleticfields.Plant breeders and researchers can find employment in thelaboratory or greenhouse, or in field research for botanicalgardens,universities,orwithprivatecompanies.Thosewithadvanced degrees in horticulture also teach at colleges anduniversities.

The cooperative extension service is a nationwide net-workassociatedwithuniversitiesineverystate.Thecoopera-tive extension offers free classes that certify you as a master

Figure 8.1 A horticultural student plucks spent flowers of Pelargonium geraniums at Colorado State University’s trial flower garden.

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gardenerinexchangeforvolunteerservicewiththeextension.You can find more information about this program at theAmericanHorticulturalSocietyWebsitelistedatthebackofthebook.

Plant collectorsOne of the more adventurous horticultural professions is that of the plant col-lector. The earliest recorded expedition was by the Egyptian queen Hatusu (Hatshepsut) in approximately 1495 b.c. The sought-after plants in this trip were those that produced frankincense and myrrh, used in Egypt for embalming, incense, cosmetics, and medicine. The live trees were trans-ported from the Land of Punt (coastal Somalia, Eastern Sudan, Eritrea) via the Red Sea, Gulf of Suez, and the Nile River.

Botanical gardens were created for scholarly purposes. The earliest botanical gardens were in European universities established in the 1500s and 1600s in France, Italy, the Netherlands, and Germany. In the 1700s, the use of a terrarium made possible the survival of many more of the plants collected on explorations, by transportation under glass on long ship voyages. Seeds or cuttings were taken from rare and endangered plants.

The USDA initiated approximately 45 plant collection expeditions in the twentieth century. The USDA horticulturists traveled around the world to col-lect specimens. One of the USDA horticulturists was Dr. Edward Corbett, a professor of horticulture at the University of Connecticut. Dr. Corbett, while employed as a research horticulturist for the USDA in 1966, accompanied Dr. Richard W. Lighty, a geneticist, on an expedition to South Korea to collect specimens of woody ornamentals. Together they endured travel over rough terrain, long boat rides, typhoons, dysentery, and sunstroke but managed to collect approximately 500 specimens, some of which still grow in Longwood Gardens, a 1,050-acre horticultural display garden in Pennsylvania. Such a trip would be more difficult today because of increased security and gov-ernment regulations that seek to limit the entry of nonnative plant species into the United States.

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You can also find out about current trends in horticulturefromperiodicalssuchasHorticulture MagazineorOrganic Gar-den, which may be in your local public library. Field trips tobotanicalgardens,universitygreenhouses, localnurseries,andgardentoursareotherwaysyoucanfurtherexploretherealmofhorticulture.

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Adventitious rootsStructuresevolvedtoabsorbwaterandminerals,whichformonastemcutting.

Agronomy Abranchofagriculturalsciencethatconcentratesoncerealgrainsandcropstofeeddomesticatedanimals.

Algal growth Greenaquaticorganismsthatgeneratecarbohydratesthroughphotosynthesis.Theirgrowthinnonpollutedwaterislimitedbyalackofnutrientssuchasphosphateornitrate.

Alkaloids Secondaryconstituentsproducedbyplantsthatareusuallypoi-sonousbutmayhavemedicinalapplications.

Aquifers Porousgeologicalfeaturesthatretainwater.

Archaeological data Skeletalremains,fossils,andevidenceofhumanactivityfoundinthesoil.

Best management practices Methodsusedtolimittheamountofchemicalfertilizerorpesticidesappliedtothesoil,whichincludesinte-gratedpestmanagementandknowledgeofplantphysiologytoapplyfer-tilizersonlyintheamountsneededbyaplantataparticulartime.

Biological control Theintentionalreleaseorcultivationofbeneficialinsectsormicrobesthatattackpeststhatfeedonplants.

Bonsai Theartofgrowingminiatureordwarfplantsbyrestrictionofrootandshootgrowth.Plantsaregrowninshallowcontainersandtherootsandshootsaremechanicallyprunedorbound.

Breeding Thedeliberatecreationofanewsubspecies(varietyorcultivar)ofplant.

carotinoid Redoryellowpigmentsfoundinleaves,whichfunctionasaccessorypigmentstochlorophyllduringphotosynthesis.

chlorophyll Greenpigmentsfoundinthechloroplast,whichfunctioninphotosynthesisbyabsorbingblueorredwavelengthsoflight.

chloroplasts Plantorganellesthatcontainchlorophyllpigmentsandarethesiteofphotosynthesis.

classification Thegroupingandnamingofplantsbasedonmorphologi-calorgeneticattributes.

climate Theprevailingweatherconditionsbasedonaveragerainfallandtemperature.

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companion plants Plantsthatprovideabeneficialservicetothegardenbyprotectingotherplantsfrominsectinfestation,microbialinfection,ornutrientdeficiency.

compost Materialproducedfromaprocessthatdegradesplantandani-malmatterintosoilorganicmattercalledhumus;atermusedinterchange-ablywithhumustodescribesoilorganicmatter.

cotyledon Firstleaforleavesthatappearaftergermination.

crop rotation Amethodofgrowingspecificplantsinadifferentbedorfieldinsuccessiveyears;itreducestheabilityofinsectpestsandmicrobialdiseaseorganismstoincreaseinpopulationbychangingthelocationoftheirhostplants.

cultivate Totillthesoiltoprepareforseedingortransplanting,forweedcontrol,andtoloosensoilthathasdevelopedacrust.

cultivars Subspeciesbredbyman.

cuttings Piecesofstem,leaf,orroottakenfromaplantandusedtoprop-agateanewplant.

deciduous Aplantthatdropsitsleavesinthewinterandgoesintoador-mantstate.

domesticated Anadjectivetodescribeananimalorplantwhichhasbeenbredforfoodandhasgeneticandmorphologicaldifferencesfromitsclos-estwildrelativethatrenderitmoreusefultohumans.

dormant Astateofrestinwhichaplantisnotactivelygrowing.

double cropping Thepracticeofgrowingtwodifferentplantsinthesameplotduringasinglegrowingseason.Usuallyoneissmallerthantheotherandmaturesearlierintheseason.Thesecondistallerandmatureslaterintheseason.

Erosion Lossofsoilduetotheactionofwindorwater.

Essential oilsVolatilesubstances,suchasalkaloidsandterpenes,thatareproducedbysomeplantsandusedforperfumeandformedicinalandculinarypurposesafteradistillationprocess.

Evergreen Aplantthatretainsitsleavesinthewinter.

Flats Rectangulartraysmadeofplasticorwoodthatareusedtogerminateseeds.

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Floriculture Abranchofhorticulturededicatedtothestudyofornamen-talplants.

Forage Avegetablefoodforanimals.

Genetic engineering Human-mediatedinsertionofforeigngenesintoaplantchromosome.

Genetically modified organisms (GMo) Plantsormicrobeswithahuman-mediatedinsertionofaforeigngene.

Geologic Relatingtothesubsurfacebeneaththesoil,whichconsistsmainlyofrock.

Grafting Combiningascionfromoneplantwiththerootstockofanother.

Groves Collectionsofcitrus,olive,orcoconuttrees.

Half-hardy Aplantabletosurviveamildfrost,butnotahardfrost,with-outinjury.

Hardy Aplantthatisabletosurviveahardfrostwithoutinjury.

Herbicides Chemicalsusedtokillaplant.

Horticulture Abranchofagriculturalsciencethatfocusesonplantsgrowninagarden,withspecialtiesinolericulture,pomology,floriculture,andlandscapeplants.

Humus Thefertileresidueofplantsandanimalmatterleftafternaturaldecompositionorthecompostprocess.Itisalsocalledcompostororganicmatter.

Hydroponics Amethodtogrowplantswithoutsoilinwatersupplementedwithnutrientsorinaspecialpottingmedia.

Indore method AtypeofcompostingdevelopedbySirHowardAlbertinIndiathatplacesspecificratiosoforganicmaterialssuchasvegetablemat-terandanimalmanuresintolargepilescalledwindrows,whichgeneratehighheatduringdecomposition.

Infestation Alargepopulationofdestructiveinsectsgatheredonaplant.

Integrated pest management (IPM) Adecision-makingprocessusedtomanageorganismsthatareharmfultoplantsthatisbasedonafundamen-talknowledgeofecology.

Invasive Aplantthatcrowdsoutnativeplantsintheecosystem.

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Irrigation Theapplicationofwatertocropsfromawellorsurfacewaterbody,suchasapondorriver,tosupplementlowrainfall.

Land-grant colleges State-runpublicinstitutionsthatteachagriculture,initiatedinthelate1800sthroughacongressionalactthatgrantedfederallandtoeachstate,whichwassoldtofundtheestablishmentofthecolleges.

Landscape horticulture Abranchofhorticulturethatspecializesintheuseofwoodyornamentalsandturf.

Last average frost date Adateinthelatespringafterwhichitisgener-allysafetoplanttenderannuals.Itiscalculatedbasedonthehistoricalaveragedateofthelastspringfrostforaparticularregion.

Leaching Themovementofwaterandsolublechemicalsdownwardthroughthesoilasaresultofgravity.

Leguminosae Afamilyofplantscharacterizedbyadehiscentdryfruit(legume)formedfromasinglecarpelthatsplitsdowntheside;manyarecapableofnitrogenfixationwithsymbioticmicrobes.

Mica Analuminosilicatemineralthatseparatesintotransparentthinsheetsorflakes.

Microbes Organismstoosmalltobeseenwithouttheaidofamicro-scope,whichincludebacteria,fungi,algae,protists,nematodes,andviruses.

Monocropping Plantingalargeplotorfieldwiththesameplantvarietyorcultivar.

Morphological Physicalcharacteristicsusedtodescribetheexternalformofaplant.

Morphology Theexternalformofanorganism.

neolithic revolution Aperiodofhumanhistorythatoccurredroughly10,000yearsagoduringthelatestperiodoftheStoneAgeandresultedindetectablenumbersofartifactsrelatedtoagricultureanditswidespreadpractice.

nitrates Aformofnitrogenfertilizerthatisverysolubleinwater.

nitrogen fixation Abilityofspecificmicrobestoconvertatmosphericnitrogentoasolublesoilmineral.

nodules Roundish,knobbystructuresfoundontherootsoflegumes

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involvedinnitrogenfixation.Theyaregeneratedbyaninteractionbetweentheplantanditsassociatednitrogen-fixingmicrobe.Noduleslimittheentryofoxygen,whichcaninhibitthereaction.

nurseries Commercialoperationsdedicatedtogrowingandsellingwoodyornamentals.

olericulture Branchofhorticulturededicatedtothestudyorproductionofvegetables.

orchards Collectionsoffruittrees,suchasapples,pears,andpeaches.

organic matter Theresultofdecomposedplant,insect,andanimalmat-terplusthemicrobesthatdecomposeit.Compostandhumusaretermsthataresometimesusedinterchangeably.

ovary Femalereproductiveorganthatcontainsovules(eggs).

Parthenocarpy Thedevelopmentoffruitwithoutfertilizationorseeds.

Pathogens Amicrobethatiscapableofcausingdisease.

Percolation Themovementofwaterdownthroughthesoiltothegroundwaterasaresultofgravity.

Petals Flowerstructuresthatmaylurepollinatorsthroughbrightcolorsorfragrance.

Pheromone Achemicalsubstancereleasedbyanorganismtoattractmembersoftheoppositesex.

Phloem Vasculartissuethattransportssugarfromtheleavestotherestoftheplant.

Phosphate Aformofphosphorousfertilizerthatisinsolubleinwaterbutmayenterintostreamsandlakesattachedtosoilparticlesthatrunoffdur-inganerosionevent.

Photoperiod Theamountoftimeperdaythataplantisexposedtolight.

Photosynthesis Plantphysiologicalprocessthatoccursinchloroplastsinparenchymacellsandusesenergyfromsunlighttocombinecarbondiox-ideandwaterintosugar.

Physiology Astudyofthephysicalandchemicalprocessesinvolvedinplantdevelopmentandgrowth.

Plantlets Clonedplantsgrowingongelatinousmedia.

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Pollination Thetransferofpollenfromthemalereproductiveorganofanangiospermplanttothestigmaofafemalereproductiveorgan.

Pomology Abranchofhorticulturethatspecializesinthestudyorgrowthoffruit.

Precipitation Rainandsnow.

Propagation Thegenerationofnewplants.

Pruning Removalofdeadbranchesorsometimeslivebranchesofwoodyplantstopromotehealthortochangetheshape.

resins Amorphous,flammablesubstancesformedinplantsecretionsthatcanbeextractedinorganicsolvents.

run off Soilandwaterfromheavyrainfallorirrigationeventsthatmoveindrainagepatternstowardssurfacewaterbodies.

Seed gene banks Collectionsofseedsusedtopreservegeneticdiversityindomesticatedcrops.

Sepals Theindividualunitsoftheouterlayerofaflowerbud.Theymaybegreenorcancloselyresemblepetals,dependinguponthespecies.

Soil pores Spacesbetweenindividualsoilparticlesandbetweenaggre-gatesofsoilparticles.

Somatic embryo Aplantembryogeneratedbytissueculturefromasomatic(nonreproductive)cellthatiscapableofgrowthtoamatureplant.

Spores Small,sometimescylindricalreproductivestructuresproducedbyseedlessplantsandsomemicrobesthatremaindormantuntilfavorableconditions,suchasmoisture,causethemtogerminate.

Stamen Partofthemalereproductiveorganinfloweringplants,com-prisedofantherswithpollensuspendedonafilament.

Stolons Modifiedstemsthatactasasexualreproductivestructuresproducedbysomeplantssuchasstrawberries.Stolonsformadventitiousrootsandshootswhentheycomeincontactwiththesoil,thusgeneratinganewplant.

taxonomy Asystemofclassificationconcernedwiththeheredityandevo-lutionaryrelationshipsoforganisms.

tender Describesanannualplantthatisinjuredbyamildfrost.

terraces Levelgardenbedsonasteepslopecreatedthroughtheuseofretainingwalls.

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terrarium Anenclosedglasschamberusedtogrowmoisture-lovingplants.

tillage Toloosenthesoilandturnit.

tilth Capabilityofasoiltosupportgrowthofgardenplants;referstothetextureandstructure.

topiary Artisticshapingofwoodyornamentalplantsbycarefulpruning.

transpiration Thelossofwaterasavaporfromleavestotheatmosphere.

transplant Tomoveaplantfromonelocationtoanother.

trichome hairs Smallfilamentousstructuresfoundonleavesorstemsthatmaybesoftorroughandmaycontainglandsthatproduceresinoressentialoil.

turf Grassthatismowedtoformalawn,golfcourse,orathleticfield.

turgor pressure Pressuregeneratedfromwaterthatentersthevacuoleinaplantcell;contributestogrowthandkeepstheplantfromwilting.

Variegated Aleafwithamottledappearance.

Vascular system Tissuethatmovesfluidsthroughaplant.

Vermiculite Alightweight,highlywater-absorbentmaterialcreatedfrommicabyexposuretohighheat.

Vernalization Periodofcoldtemperaturerequiredbycertainplantsbeforetheywillproduceflowers.

Very tender Describesanannualplantthatcanbekilledbyamildfrost.

Viable Abletogrowandreproduce.

Viticulture Thestudyorprocessofgrowinggrapes.

Weeds Plantsthatcompetewithcropsorgardenplantsforwaterandnutrients.

Woody ornamentals Plantswithalateralmeristemthatgeneratessecond-arygrowthandresultsinanincreaseinthediameterofthestem.Treesandshrubsareexamples.

Xeric Aclimatecharacterizedbycool,wetwintersandhot,drysummers.Thetermisalsoappliedtoplantsthatthriveinthistypeofclimate.

Xylem Vasculartissuethattransportswaterfromtherootsuptootherpartsoftheplant.

Yield Theharvestedportionofacropmeasuredinunitsorbyweight.

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Anisko,Tomasz.Plant Exploration for Longwood Gardens.Portland,Ore.:TimberPress,2006.

Ashworth,Suzanne.Seed to Seed.Decorah,Iowa:SeedSaversExchange,1991.

Bailey,L.H.How Plants Get Their Names.Mineola,N.Y.:DoverPublications,1963.

Bradley,FernMarshallandBarbaraW.Ellis.Rodale’s All-New Encyclopedia of Organic Gardening: The Indispensable Resource for Every Gardener.Emmaus,Pa.:RodalePress,1992.

Brickell,ChristopherandJudithD.Zuk.The American Horticultural Society A–Z Encyclopedia of Garden Plants.NewYork:DKPublishing,1996.

Campbell,NeilA.Biology 4thed.MenloPark,Calif.:Benjamin/CummingsPublishingCompany,1996.

Childe,GordonV.TheDawn of European Civilization,6thed.NewYork:AlfredA.Knopf,Inc.,1958.

deCandolle,Alphonse.Origin of Cultivated Plants,Reprintof2nded.(1886).NewYork:HafnerPublishingCompany,1959.

Ellis,BarbaraW.andFernMarshallBradley.Organic Gardener’s Handbook of Natural Insect and Disease Control: A Complete Problem-Solving Guide to Keeping Your Garden and Yard Healthy without Chemicals.Emmaus,Pa.:RodalePress,1992.

Fedoroff,NinaV.andNancyMarieBrown.Mendel in the Kitchen: A Scientist’s View of Genetically Modified Foods.Washington,D.C.:JosephHenryPress,1999.

Fernald,M.L.Gray’s Manual of Botany: A Handbook of the Flowering Plants and Ferns of the Central and Northeastern States and Adjacent Canada,8thed.Illustrated.NewYork:D.VanNostrandCompany,1970.

Flint,MaryLouiseandSteveH.Dreistadt.Natural Enemies Handbook: The Illustrated Guide to Biological Pest Control.Berkeley,Calif.:UniversityofCaliforniaPress,1998.

Friederici,Peter.“Earthwormedover.”AudubonMarch2004:28.

Fuller,AndrewS.The Small Fruit Culturist.NewYork:JuddOrangeandCompany,1867.

Hancock,JamesF.Plant Evolution and the Origin of Crop Species, 2nded.Cambridge:CABIPublishing,2004.

Harlan,JackR.Crops & Man.Madison,Wisc.:AmericanSocietyofAgronomy,CropScienceSocietyofAmerica,1975.

116

Harlan,JackR.The Living Fields: Our Agricultural Heritage. Cambridge:CambridgeUniversityPress,1995.

Janik,Jules.Horticultural Science,4thed.NewYork:W.H.FreemanandCompany,1986.

Kohnke,HelmutandD.P.Franzmeier.Soil Science Simplified,4thed.ProspectHeights,Ill.:WavelandPress,1995.

Martin,DeborahL.andGraceGershuny.Rodale Book of Composting. Emmaus,Pa:RodalePress,1992.

Mithen,Steven.After the Ice: A Global Human History, 20,000–5000 B.C. . London,UK:WeidenfeldandNicolson,2003.

Nelson,PaulV.Greenhouse Operations and Management,4thed.EnglewoodCliffs,N.J.:Prentice-Hall,1991.

Poincelot,RaymondP.Sustainable Horticulture: Today and Tomorrow. UpperSaddleRiver,N.J.:PearsonEducation,2004.

Pollen,Michael.“ExploringtheSafetyandEthicsofGeneticallyEngineeredFoods,”inGenetically Engineered Foods, NancyHarris,ed.Farmington,Mass.:GreenhavenPress,2004:13–29.

Rabalais,N.N.,R.E.Turner,andD.Scavia.“BeyondScienceintoPolicy:GulfofMexicoHypoxiaandtheMississippiRiver.”BioScience52(2002):129–142.

Raven,Peter,RayF.Evert,andHelenaCurtis.Biology of Plants, 2nded.NewYork:WorthPublishers,1976.

Smith,MirandaandtheNortheastOrganicFarmingAssociationandCooperativeExtension.The Real Dirt: Farmers Tell About Organic and Low Input Practices in the Northeast.Burlington,Vt.:NortheastRegionSustainableAgricultureResearchandEducation(SARE),1994.

Storl,WolfD.Culture and Horticulture: A Philosophy of Gardening.Wyoming,R.I.:Bio-DynamicLiterature,1979.

Swiader,JohnM.,GeorgeW.Ware,andJ.P.McCollum.Producing Vegetable Crops,4thed.Danville,Ill.:InterstatePublishers,1992.

Taiz,LincolnandEduardoZeiger.Plant Physiology.RedwoodCity,Calif.:TheBenjamin/CummingsPublishingCompany,1991.

Valpuesta,Victoriano.Fruit and Vegetable Biotechnology.BocaRaton,Fla.:CRCPress,2002.

Verzole,Roberto.“GeneticallyEngineeredFoodsHaveHealthRisks,”inGenetically Engineered Foods, NancyHarris,ed.Farmington,Mass.:GreenhavenPress,2004:38–42.

117

vonLinne,Carl.Linnaeus’ Philosophica BotanicatranslatedbyStephenFreer.NewYork:OxfordUniversityPress,2003.(FirstpublishedinLatinin1751inStockholm.)

Ward,BobbyJ.The Plant Hunter’s Garden: The New Explorers and Their Discoveries.Portland,Ore.:TimberPress,2004.

Zohary,DanielandMariaHopf.Domestication of Plants in the Old World: The Origin and Spread of Cultivated Plants in West Asia, Europe and the Nile Valley, 3rded.NewYork:OxfordUniversityPress,2000.

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Appelhof,Mary.Worms Eat My Garbage: How to Set Up and Maintain a Worm Composting System.Kalamazoo,Mich.:FlowerPress,1982.

Bix,Cynthia,PhilipEdinger,andtheEditorsofSunsetBooks.Arranging Flowers from Your Garden.MenloPark,Calif.:SunsetPublishingCorporation,2002.

Coleman,Eliot.The New Organic Grower: A Master’s Manual of Tools and Techniques for the Home and Market Gardener.WhiteRiverJunction,Vt.:ChelseaGreenPublishingCompany,1995.

Doty,WalterL.All About Vegetables.SanRamon,Calif.:OrthoBooks(MonsantoCompany),1990.

Jeavons,John.How to Grow More Vegetables. Berkeley,Calif.:TenSpeedPress,1995.

Kowalchik,ClaireandWilliamH.Hylton,Eds.Rodale’s Illustrated Encyclopedia of Herbs.Emmaus,Pa.:RodalePress,1998.

Ondra,NancyJ.andSaxonHolt.Grasses: Versatile Partners for Uncommon Garden Design.NorthAdams,Mass.:StoreyBooks,2002.

Riotte,Louise.Carrots Love Tomatoes: Secrets of Companion Planting for Successful Gardening.Pownal,Vt.:StoreyCommunications,1975.

Stickland,Sue.Greenhouses: Natural Vegetables, Fruit, and Flowers All the Year Round.Coventry,UK:TheHenryDoubledayResearchAssociation,1993.

Wilson,GilbertL.Buffalo Bird Woman’s Garden: Agriculture of the Hidatsa Indians.St.Paul,Minn.:MinnesotaHistoricalSocietyPress,1987.

Web SitesAmerican Horticultural Society

www.ahs.org/master_gardeners/index.htm

This Web site has a link to the horticultural cooperative extension Master Gardening Program and links to various publications.

Environmental Protection Agencyhttp://www.epa.gov

This site has information on pesticides and legislation for the conserva-tion of water and soil.

National Association of State Universities and Land-Grant Collegeswww.nasulgc.org/campus.htm

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Land-grant college Web sites have links to the horticultural cooperative extension for your state, which provide fact sheets online and can rec-ommend a soil testing lab.

Natural Resources Conservation Services http://www.nrcs.usda.gov

This site has a link where teachers and students can find out about con-servation of soil and water with Backyard Conservation Tip sheets. There is also a plant database.

USDA Web site http://www.usda.gov

This site has links for information on organic certification and commer-cial horticultural crops.

United States National Arboretumhttp://www.usna.usda.gov

This site has an interactive USDA Plant Hardiness Zone Map, virtual tours and plant galleries of woody ornamentals, a list of state trees and flowers plus horticultural links with information on pest management.

The following sites offer virtual tours, image galleries, and links to garden and horticultural information on plants from different ecosystems.

Brooklyn Botanic Garden (http://www.bbg.org) is in New York City.

Denver Botanic Garden (http://www.botanicgardens.org) is in Colorado.

Desert Botanic Garden (http://www.dbg.org) is in Arizona.

Hawaii Tropical Botanical Garden (http://www.htbg.com) is in Hawaii.

Longwood Gardens (www.longwoodgardens.org) is in Pennsylvania.

Missouri Botanic Garden (http://www.mobot.org) is in St. Louis.

Royal Botanic Gardens: Kew (http://www.rbgkew.org.uk) is in England.

The Berry Botanic Garden (http://www.berrybot.org) is in Oregon.

United States Botanic Garden (http://www.usbg.gov) is in Washington, D.C.

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agronomy,defined,4Albert,Howard,12alkalinity,53–54alkaloids,22allergies,44allochemicals,69angiosperms,18–19,23animalpests,73–74annualplants,22auxins,40

Bacillussp.,66–67,72Bacillus thuringiensis(Bt),72beddingplants,87,88binomialnomenclature,25–26biofuels,81biogeochemistry,52biologicalcontrol,15,72bioterrorism,80,84bloodmeal,55Botyris cinerea,75,76,86Boussingault,JeanBaptiste,8breeding,41–44bryophytes,18Burbank,Luther,41–42

calciumcarbonate,54–55calli,40capillaryaction,85capitalization,26carbondioxide,86,88careers,104carotenoids,24cereals,6chemicals,10–12,41,85chlorophyll,24chloroplasts,48,49classificationofplants,18–24claysoils,51,52climate,60climbingplants,76–77coldtreatment,33–34colleges,15,104

ColoradoRiver,80–81commercialhorticulture,80–89commonnames,28communitygardens,101compaction,51companioncrops,14,72composting,10,12–14,52,65–66,70conifers,19containergardens,98conventionalproduce,7–12Corbett,Edward,106cornblight,84cotyledons,19criticalnightlength,50croprotation,7,14,67–68crowding,75crusts,75cultivars,26–27,81culturalrequirements,48–51,51–53,

56–60cuttings,6,36–39cycads,19cytokinins,40

Darwin,Charles,41–42DeadZone,12deadheading,75deciduousplants,24deer,73,74dichotomouskeys,28dicotyledons,19,21,22,23diseases,67,74,84diversity,81–83division,75–76DNA,44dormancy,32–33doublecropping,7dripirrigation,57–59droughttolerantplants,59drupes,25

earthworms,65–66ebbandflowsystem,85

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Encyclopedia of Organic Gardening,14entomology,69ethylene,88–89

fertilizers.See alsocompostingcommercialhorticultureand,81conventionalmethodsand,10,

11–12organicgardeningand,14,55–56soilalkalinityand,54transplantationand,41

fieldheat,89floriculture,5,87,104flowers,5,19,28,33–35,50fluoride,57FoodandDrugAdministration(FDA),

44forestry,4foxtail,68frankincense,106frost,35–36frozen-foodindustry,81fruits,5,25,88–89fungi,59–60,66,75

gardens,92–96,96–101genebanks,84geneticdiversity,81–83geneticallymodifiedorganisms

(GMOs),14,39,42–44genusnames,26geormin,66germinationrequirements,32–33gnetinae,19grafting,7,38grapes,5grayrot,75,76greenmanuring,66,68–69greenhousecrops,83–87greensand,55groundwater,11–12,80gymnosperms,18–19gypsum,54–55

half-hardiness,35handpollination,41handling,post-harvest,89hardiness,34–35,92harvesting,87–89herbariums,28–29herbicides,12,69herbs,22hibiscus,21hoes,68hormones,40horticulturetherapists,104houseplants,87humidity,59humus,10,52hybrids,28hydroponics,8–10,84–85

Indoremethod,12infraredlight,51insecticides,10–11,67–68,72–73,85insects,34–35,69–73,85–86integratedpestmanagement(IPM),

15,64–72,73–77intensity,light,48–49,51irradiation,41irrigation,7,56–59,80–81

jobs,104

K.Seepotassium

landbeetles,71land-grantcolleges,15,104landscapearchitects,104landscapehorticulture,5lastaveragefrostdate,34,35–36Latin,26,28leaching,12legumes,25,55–56,66Leguminosaefamily,22,23Liebeg’sLawoftheMinimum,52–53

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light,48–51,86Lighty,RichardW.,106lilies,20,23lime,54–55Linnaeus,Carolus,26,27loams,51location,selectionof,92–93LowInputSustainableAgriculture

(LISA)program,15

macronutrients,52maintenance,overviewof,74–77media,36meristemcells,40methylbromide,67microbes,10,13–14,64–66,70,85microclimates,98micronutrients,52–53minerals,8–10,51,53–54moisture.SeewaterMollison,Bill,14monocotyledons,19,20,22,23monocropping,10,67–68,73,81–83mulching,67,75mutations,breedingand,41mycorrhizalfungi,66

namingofplants,24–29nightlength,50nitrates,12nitrogen,55,56,66nitrogenfixation,22,66,70nodules,22nutrients,36,52–53,55,70,74

olericulture,5orchards,5orchids,39organicgardening,55–56,74–75organicmatter,10,52organicproduce,12–15ovaries,18–19,25oxygen,56,70

parenchymacells,39–40parthenocarpicfruits,25,42pathogens,65,66–67perennialplants,22,75–76,92permaculture,14pesticidedrift,81pesticides,10,14–15,33,42–43,81,85pests,69–74pH,53–55,56,74–75pheromonetraps,85–86phloem,19phosphorus,55,56photoperiod,50–51photosynthesis,19,48,49phyllosphere,69–73pigments,24,50pollination,7,34–35,41,69pomology,5ponds,94post-harvesthandling,89potassium,54–56potatoes,41,81,82predators,73pretreatments,33–34propagation,32–36,36–39,39–44pruning,7,77Pseudomonas,67

rain.Seewaterraisedbeds,96,97resins,22retainingwalls,100rhizomes,38rhizosphere,64–69ripening,88–89rockphosphate,55Rodale,J.I.,14roots,38,41,57–59rot,gray,75,76rototillers,96

salts,54sandysoils,51

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seeds,18–19,32–36,84selfers,34shadecloth,49,86silica,53smothercrops,69soakerhoses,57–59soil,51–53,64–69,80–81,93,96solstice,50–51solublesalts,53–54somaticembryos,40speciesnames,26spores,18,59–60staggeredplanting,72Steiner,Ralph,13stickycards,85stolons,38Streptomyces,66sunshine.SeelightSustainableAgricultureandResearch

Education(SARE),15sustainablehorticulture,15

taproots,40temperature,32–33,59,70,86,98tenderness,35terraces,101terrariums,106texture,51thinning,75tillage,10,12tilling,96tilth,51tissueculture,39–40traceelements,52–53tracheophytes,18–19transgenicplants,14,39,42–44

transpiration,56,59transplantation,40–41transposableelements,44trapcrops,72trichomehairs,22turgorpressure,56

UnitedStatesNationalArboretum,36,60,92

urbansprawl,81USDA,14,60,106

varieties,26–27vascularsystem,18–21vegetables,5,26–27ventilation,86vermiculite,85vernalization,32–33viticulture,5VonLiebig,Justus,8

water,32–33,36,56–60,80,84–85wavelength,50weeds,10,38,66,68–69wildflowers,52wind,34windbreaks,95,98wine,5woodashes,54–55

xericplants,59X-rays,41xylem,19

yields,10

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Gail M. Langhasstudiedplantsformorethan20years.SheholdsaPh.D.inenvironmentalmicrobiologyfromColoradoStateUniversity,anM.S.ingenetics,andaB.S. inagronomy fromtheUniversityofConnecticut.Shehas professional experience in the commercial greenhouse and botanicalgarden;hasconductedresearchinthefield,laboratory,andgreenhouse;andwasaninspectorforcertificationoforganicfarms.ShecurrentlygardensinthefoothillsoftheRockyMountainsandresearchesplantbiodiversityatanavianpreserve.

Horticulture - Higher Intellect · Horticulture Gail M. Lang, Ph.d. Series Editor William G....

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