Flowering Bulbs

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Transcript of Flowering Bulbs

  • 1Agricultural Extension ServiceThe University of Tennessee

    PB 1610

    Flowering

    GardensTennesseeBulbs for

  • 2ContentsBulbs ........................................3Corms .......................................3Tubers .......................................3Rhizomes .....................................4Culture ......................................4

    Introduction ................................4Site Selection................................5Site Preparation..............................5Selecting Plant Material ........................5

    Planting Spring-Flowering Geophytes................6Iris .......................................6

    Planting Summer-Flowering Geophytes ..............7Caladium ..................................7Canna .....................................8Dahlia .....................................8Gladiolus ..................................9

    Maintenance of Geophytes ....................... 10Forcing Spring-Flowering Geophytes in the Home ... 11Forcing Tender Geophytes in the Home ........... 12Amaryllis ................................. 12

    Dictionary of Bulbous Plants...................... 13The Bulb Selector .............................. 21Mail Order Sources ............................ 22U.S.D.A. Hardiness Zone Map.................... 23

  • 3A wealth of spring-,summer- and fall-flowering bulbs canbe used to extend the gardenfloral display from earlyspring until late fall. Some ofthese will be winter hardyand remain in the groundyear-round. Others will notsurvive freezing temperaturesand must be replanted eachspring. Many are not eventrue bulbs, but are often soldalong side true bulbs in mailorder catalogs and at gardenstores. The different types ofunderground storage struc-tures that are frequentlycalled bulbs include corms,tubers, tuberous roots, tuber-ous stems and rhizomes.These underground storagestructures collectively arecalled bulb-forms or geo-phytes. Geophyte comes fromthe Greek word geo mean-ing earth, and the Greekword phyte meaninggrowth or plant; therefore,geophyte means earthgrowth or earth plant.

    Bulbs:The true bulb

    consists of amuch-com-pressed, fleshystem, the basalplate. Attachedto the basal plate

    are thick, fleshy, modifiedleaves, the scales. The scalesare organized to form twodistinct types of bulbs. Lami-

    nate (tunicate)bulbs areconcentric,cylindricalscales. Theouter layers ofscales becomedry and

    papery, forming the tunic.This protects the bulb fromdisease, insect and mechani-cal damage. Daffodil andonion are common tunicatebulbs. The scaly (non-tuni-cate) bulb has numerousindividual scales whichreadily break off the basalplate. This bulb has no tunic,making it somewhat moresusceptible to disease, insectand mechanical damage. Lilyis a common scaly bulb.

    Corms:A corm is

    the swollenbase of a stemwith typicalstem parts:nodes and internodes. Thedry, papery leaf bases en-close the swollen stem base,forming the protective tunic.The tunic, as with the bulbtunic, protects the corm fromdisease and water loss. A

    corm does notpersist fromseason toseason. Rather,a new corm isformed abovethe old corm formed theprevious year. Gladiolus andcrocus are the two mostcommonly grown corms.

    Tubers:Tubers are

    producedwhen the tipsof a stolon (ahorizontallygrowing stemjust at the soilline) becomesswollen from stored foods.Tubers are formed belowground. Close examination ofthe tuber will reveal typicalstem structures of nodes, theeyes of a potato and intern-odes. Besides the Irish po-tato, another commonlygrown tuber is caladium.

    The tuberous root and thetuberous stem are commonlymislabeled as tubers. Thetuberous rootforms from theswelling of roots.Tuberousroots donot haveany fea-tures

    Lily

    Daffodil

    Crocus

    Gladiolus

    Caladium

    Dahlia

    Flowering Bulbsfor Tennessee Gardens

    Mary Lewnes Albrecht, Professor and HeadOrnamental Horticulture and Landscape Design

  • 4common to stems (there areno nodes or internodespresent); they have all theinternal and external featuresof roots.

    On the other hand, thetuberous stem does havefeatures of stems. The tuber-ous stem forms from theswelling of the area of theplant known as the hypo-cotyl. This is the transitionregion between the root andthe stem.

    Tuberous roots are formedon the sweet potato and thedahlia. Tuberous stems areformed by tuberous begonias,cyclamen and gloxinia.

    Rhizomes:A rhizome is a specialized

    stem which grows just at orbelow the soil surface. There

    are many economicallyimportant plants which

    form rhizomesincludingbamboo,iris, lily-of-the-

    valley and many grasses.There are two types of

    rhizomes found in nature,leptomorphic rhizome andpachymorphic rhizome. Thelily-of-the-valley has aleptomorphic rhizome: a verythin rhizome with indetermi-nate growth (the rhizomedoes not terminate in a flowerstalk; it remains vegetative),branches freely and formsmany flowering shoots.Plants withleptomorphic rhizomescan formverydensemats.

    The pachymorphic rhizomeis a large, fleshy, horizontalstem which has determinategrowth. Once the terminalgrowing point or meristem ofthe rhizome forms an inflores-cence (the flower stalk), therhizome will form two branchesbehind the meristem. Thebearded iris is a very commonpachymorphic rhizome.

    Culture:Introduction

    Geophytes are normallygrouped based upon theirability to withstand freezingweather. Knowing thisinformation is essential toproper culture.

    Hardy geophytes, onceplanted and established, willsurvive freezing temperaturesunder normally good growingconditions. Examples of hardygeophytes are narcissus, tulip,hyacinth, crocus, lily andbearded iris. Semi-hardyspecies may be hardy insomewhat milder climates, butcannot be relied upon tosurvive extended exposure tobelow-freezing temperatures.Many of the anemones,ranunculus, bulbous iris andcannas fall into this class.

    Those species which willnot tolerate hard-freezingtemperatures and can only beleft in the ground in warmclimates are referred to astender. This includes many ofour summer-flowering geo-phytes such as dahlia, gladi-olus, caladium, callas andtuberous begonia.

    The bulbous plants can beused in a number of ways

    and make an attractive addi-tion to gardens: perennialborder, naturalized areas,rock gardens, foundationplantings, flower borders andcontainers. Areas to avoidinclude painted walls, pavedwalks or driveways. Reflectedheat from these areas duringmidday through late after-noon can cause damage tomost plants. If such an area ischosen, the plants will de-velop and flower faster. Themain disadvantage is thefoliage will die back morequickly due to excessive heat.

    This will result in bulb de-cline, since not enough foodwill be stored before completedie-back occurs. Plantingunder trees with surface rootssuch as Norway maple, beechor linden should be avoided,since there will be competi-tion between tree roots andbulbs for necessary moistureand nutrients. For the samereason, vigorous shrubs, suchas forsythia and Pfitzer juni-pers, and dense ground

    Iris

    Calla-lily

    Lily

  • 5covers, such as ivy, pachys-andra or creeping euonymus,should also be avoided. Manylarger spring-flowering,bulbous plants will competesuccessfully with the groundcover Vinca minor, periwinkle.Also consider adding many toperennial beds where theperennials can actually hidethe unsightly bulb foliage asit dies.

    Site SelectionWhen choosing a site,

    consider sunlight, drainageand air circulation. Mostgeophytes require a minimumof five to six hours of dailysunlight. Notable exceptionsare lily-of-the-valley andcaladium, which can thrive inshade (see the Dictionary ofBulbous Plants and The BulbSelector lists at the end of thispublication for others). Formaximum growth from yearto year, eight to 10 hours ofsunlight are better. Adequatesunlight results in largerblooms and healthier, hardierplants due to the ability tomaximize photosynthesis.

    A sandy loam is the besttype of soil for geophytes,since it has very good drain-age coupled with good water-holding capacity. To check anarea for drainage, dig a holeabout 1 foot deep and fill itwith water. Come back thenext day and fill it again. Ifthis second application ofwater drains completely ineight to 10 hours, the soil hasadequate drainage. If not, thesoil most likely has a high claycontent and organic amend-ments such as compost, leafmold or peat moss should be

    added to improve drainage.The third essential criteria

    is adequate air circulation. Aircirculation is necessary toreduce the incidence of dis-ease with these plants.

    Site PreparationIf the chosen site has poor

    drainage, several things canbe done. Drain pipes can belaid to facilitate the removal ofexcess water. If this is notdesirable or feasible, addingorganic matter to a heavy claysoil will improve drainage.Adding up to 30 percentorganic matter by volume willmake a difference (spread a 4-inch thick layer of organicmatter over the bed then till itinto the soil to a depth of 12inches). Adding organicmatter from composts willalso aid sandy soils wheredrainage is too rapid andwater-holding capacity isreduced. If the area has suchpoor drainage that organicmatter incorporation will notbe of much benefit, raisedbeds can be constructed.Materials such as landscapetimbers, stone or brick can beused to build raised beds.Walls can be made highenough for use as additionalseating in the smaller gardensof todays urban settings.Regardless of the methodchosen to improve drainage, itis essential that the soil isprepared to a 12-inch depth sofertilizers are placed in therootzone. Bonemeal, at therate of 4 to 6 pounds per 100square feet of bed area, willprovide plants with phospho-rus, calcium, manganese andsome nitrogen. A reported

    problem using bonemeal is