Agaricus Mushroom Growing

16
for Agaricus Mushroom Growing Basic Procedures College of Agricultural Sciences Agricultural Research and Cooperative Extension

Transcript of Agaricus Mushroom Growing

Page 1: Agaricus Mushroom Growing

forAgaricus MushroomGrowing

Basic Procedures

College of Agricultural SciencesAgricultural Research and Cooperative Extension

Page 2: Agaricus Mushroom Growing

2

Introduction

Hippocrates first mentioned mush-rooms when he wrote about theirmedicinal value in 400 B.C. The firstmention of mushroom cultivation,distinct from a chance appearance inthe field, was in l652. Unfortunately,they were described as excellent for“making into compresses for ripeningboils” but not as good to eat. In l707,a French botanist wrote about mush-rooms as “originating from a horse.”He went on further to note, “Sporesupon germination developed into afluff, this fluff, planted into horsemanure and covered with soil, wouldgrow mushrooms.” The first record ofyear-round commercial productionwas in l780 when a French gardenerbegan to cultivate mushrooms in theunderground quarries near Paris. Afterthe Civil War, gardeners introducedmushroom growing to North Americaby using dark areas underneathgreenhouse benches to grow mush-rooms.

In spite of some articles that saymushrooms can be grown in any darkhole or building, successful commer-cial mushroom growing requiresspecial houses equipped with ventila-tion systems. While mushrooms areusually grown in the absence of light,darkness is not a requirement. Mush-rooms have been grown in unusedcoal and limestone mines, old brewer-ies, basements of apartment houses,natural and man-made caves, rhubarbsheds, and many other unusualstructures. Mushrooms were report-edly grown in an old dairy barn,which was so damp that cows living init had died of pneumonia. In l894, thefirst structure specifically designed togrow mushrooms was built in ChesterCounty, Pennsylvania, which isusually referred to as the mushroomcapital of the world.

Growing mushrooms is a waste-recycling activity. Mushroom farmsbenefit the environment by usingmany tons of mulch hay, straw-bedded horse manure, and poultrymanure. These products are consid-ered agricultural waste products andwould not have a home if it were notfor mushroom production. Mush-room production is both an art and ascience with many complex anddistinct stages.

This fact sheet will outline the overallmushroom production cycle and givea brief description of each of theproduction stages. Phase I and PhaseII composting, spawning, spawncolonization (Phase III), casing, caserun, pinning, and harvesting are theprimary stages of the mushroomproduction cycle. The specific criteria(temperature set points, carbondioxide concentrations, and so forth)involved in each stage will changedepending on different mushroomcrops and different mushroomgrowers, but the basic concepts andmethods of mushroom productionremain constant. Although a writtendescription of mushroom growingmay seem simple, the process ofpreparing a composted substrate andits pasteurization is quite complex.Potential growers are encouraged togain cultural experience on an existingfarm before embarking on a privateenterprise.

A few mushroom farms are located inlimestone caves where the rock acts asboth a heating and cooling surface,depending on the time of the year.Mushroom growing is not necessarilyappropriate for caves or abandonedcoal mines since they have too manyintrinsic problems to be consideredreliable sites for mushroom farms. Thesame is true for other dark, humidspaces of any sort. Limestone cavesrequire extensive renovation and

improvement before they are suitablefor mushroom growing. Compostingtakes place above ground on a wharf,and only growing and harvestingoccur in the cave.

A Review of MushroomGrowing

The mushroom is a fungus and isquite finicky about its food source.Mushrooms lack the ability to useenergy from the sun. They are notgreen plants because they do not havechlorophyll. Mushrooms extract theircarbohydrates and proteins from arich medium of decaying, organic-matter vegetation. This rich organicmatter must be prepared into nutri-ent-rich substrate composts that themushroom can consume. Whencorrectly made, this food may becomeavailable exclusively to the mushroomand would not support the growth ofmuch else. At a certain stage in thedecomposition, the mushroom growerstops the process and plants themushroom so it becomes the domi-nant organism in that environment.

The sequence used to produce thisspecific substrate for the mushroom iscalled composting or compost sub-strate preparation and is divided intotwo stages, Phase I and Phase II. Eachstage has distinct goals or objectives. Itis the grower’s responsibility toprovide the necessary ingredients andenvironmental conditions for thechemical and biological processesrequired to complete these goals. Themanagement of starting ingredientsand the proper conditions forcomposting make growing mush-rooms so demanding.

Page 3: Agaricus Mushroom Growing

3

Making a CompostedSubstrate

Many agricultural by-products areused to make mushroom substrate.Straw-bedded horse manure and hayor wheat straw are the common bulkingredients. “Synthetic” composts arethose in which the prime ingredient isnot straw-bedded horse manure. Ifbulk ingredients are high in nitrogen,other high-carbohydrate bulk ingredi-ents—such as corncobs, cottonseedhulls, or cocoa bean hulls—are addedto the mix. All compost formulasrequire the addition of nitrogensupplements and gypsum.

Additional nitrogen-rich supplementsare added to composts to increase thenitrogen content to 1.5–1.7 percentfor horse manure or 1.7–1.9 percentfor synthetic; both are computed on adry weight basis. Poultry manure isprobably the most common andeconomical source of nitrogen. Avariety of meals or seeds, such ascottonseed meal, soybean meal, orbrewer’s grain may also be used.Inorganic or nonprotein nitrogensources such as ammonia nitrate andurea are also used, but only in smallamounts when high-carbohydratebulk ingredients are used. Gypsum isadded to minimize “greasiness” and tobuffer the pH of the compost.Gypsum increases the flocculation ofcolloids in the compost, whichprevents the straws from stickingtogether and inhibiting air penetra-tion. Air, which supplies oxygen to themicrobes and chemical reactions, isessential to the composting process.Gypsum may be added early in thecomposting process, at 70–100 lbs perton of dry ingredients.

A concrete slab, referred to as a wharf,is required for composting (Figure 1).In addition, a compost turner toaerate and water the ingredients and atractor-loader to move the ingredientsto the turner are needed. Water usedduring a substrate preparation opera-tion can be recycled back into theprocess. It is, in a sense, a closedsystem. Water runoff into the environ-ment is nonexistent on a properlymanaged substrate preparation wharf.Water collected in concrete pits or asealed lagoon is aerated and recycledto soak bulk ingredients before thecomposting process begins.

Conventional Phase I compostingbegins by mixing and wetting theingredients as they are stacked. Mostfarms have a preconditioning phase inwhich bulk ingredients and somesupplements are watered and stackedin a large pile for several days tosoften, making them more receptiveto water. This preconditioning timemay range from 3 to 15 days. Thepiles are turned daily or every otherday. After this pre-wet stage, thecompost is formed into a rectangularpile with tight sides and a loose center.A compost turner is typically used toform this pile. Water is sprayed ontothe horse manure or synthetic com-post as these materials move throughthe turner. Nitrogen supplements andgypsum can be spread over the top ofthe bulk ingredients and are thor-oughly mixed by the turner.

Figure 1. Traditional compost wharf, showing pre-wet pile on the right and thericks or windrows on the left.

Page 4: Agaricus Mushroom Growing

4

Figure 2 is a close-up of a machine“eating” its way through a compostpile. Once the pile is wetted andformed, aerobic fermentation(composting) commences as microbialgrowth and reproduction naturallyoccur in the bulk ingredients. Heat,ammonia, and carbon dioxide (CO

2)

are released as by-products during thisprocess. Compost activators, otherthan those mentioned, are not needed.

As temperatures increase above 155ºF(70ºC), microorganisms cease growingand a chemical reaction begins.Concentrating and preserving com-plex carbohydrates is one goal ofPhase I. The quantity and the qualityof nitrogen in the system are changedto a type of nitrogen that Phase IImicroorganisms and, eventually, themushroom will use as food.

Adequate moisture, oxygen, nitrogen,and carbohydrates must be presentthroughout the process; otherwise, theprocess will stop. This is why waterand supplements are added periodi-cally and the compost pile is aerated asit moves through the turner. Oxygen-ation is achieved in conventionaloutdoor ricks by natural convection.The high pile temperatures drawambient air through the sides of thestack, and as the air is heated, it risesupward through the stack—a processcommonly referred to as the chimneyeffect (Figure 3). The sides of the pileshould be firm and dense, yet thecenter must remain loose throughoutPhase I composting. The exclusion ofair results in an airless (anaerobic)environment. As the straw or haysoftens during composting, thematerials become less rigid and morecompact while substrate densityincreases. Thus, less air reaches thebottom and center of the pile. A lackof oxygen may occur after the largequantities of water are added to thedry bulk ingredients and before

sufficient heat is generated to start thedraw of air into the pile. Underanaerobic conditions, organic acidsand other deleterious chemicalcompounds are formed. Therefore,

preparing substrate under aerobicconditions, where less offensive odorsare produced, is better for mushroomgrowers.

Figure 2. Self-propelled compost turner moving through a compost rick or pile.

Figure 3. Cross section of a compost pile showing the different temperaturezones and air movement (blue arrows) caused by the chimney effect.

Outerr cooleertempeeratureezone

Anaerobiccore zone

Hot, optimum compostingtemperature zone

Page 5: Agaricus Mushroom Growing

5

Aerated Phase IComposting

Improving community relations hasled to alterations in the way the PhaseI mushroom composting process iscarried out. As urban areas encroachon rural farmland, residents havemade odor-related complaints andlegal battles have ensued, whichsuggest a need for more stringentodor-management practices.

If the pile is not turned and aeratedduring Phase I composting, oxygenmay become limited and anaerobicconditions may develop along thebottom of the stack. As the anaerobic

core gets larger, more offensive odorsare produced. In order to maintainaerobic conditions throughout theentire substrate pile, supplementalaeration is sometimes used. Thisaeration is accomplished by using afan to force air up through a concretepad with a series of evenly distributedopenings and into the substratematerial. This design is referred to asan aerated floor. Systems have beenbuilt with structural sidewalls, usuallyof concrete and occasionally of wood,to form the piles with a uniformheight and depth (Figure 4). Asidefrom aerated floors and structuralsidewalls, there is great variationamong bunker systems currently beingused for Phase I.

Aerated composting systems arereplacing conventional ricks through-out Europe and are beginning to gainacceptance in North America as thequest to manage odors continues.Europeans were the first to regulateemissions from their agriculturaloperations. Therefore, most Europeanmushroom composting operationshave employed some type of enclosedor environmentally controlled Phase Isystem. In North America, a fewsystems have been built to test thetechnology. Eventually they maybecome common at commercialoperations. Unfortunately, littleinformation is available to show howthese systems reduce emissions.Therefore, determining how effectiveaerated systems are in reducing odorsis difficult.

Phase I is considered complete as soonas the raw ingredients become pliableand are capable of holding water, theodor of ammonia is sharp, and thedark-brown color indicates thatcarmelization and browning reactionshave occurred. At the beginning ofPhase I, the substrate is bulky andyellow. At the end of Phase I substratepreparation, the substrate should bedense, chocolate brown in color, andhave a strong odor of ammonia. Thesubstrate still has some structure soaeration can be maintained duringPhase II composting. The potentialfresh mushroom yield depends on theamount of dry weight filled. In orderto achieve a substrate density in thegrowing structure necessary to supportan economical mushroom yield, thesubstrate at fill has to be short ordense enough to attain a high sub-strate dry weight.

Figure 4. This aerated substrate preparation system has a piped concrete floorunder the substrate that forces air through the substrate to maintain aerobicconditions during the composting process.

Page 6: Agaricus Mushroom Growing

6

Growing Systems(Phase II)

Once Phase I is complete, the sub-strate will be filled into a system forPhase II substrate preparation and togrow the mushrooms. Phase II takesplace in one of three main types ofmushroom-growing systems, depend-ing on the type of production systemused. The difference in the mush-room-growing systems is the containerin which the crop is processed andgrown. With a multizone system, thesubstrate is filled into boxes or traysand moved from room to room asshown in Figure 5. Each room has adifferent heating, ventilating, and air-conditioning (HVAC) system de-signed for a specific stage in cropdevelopment. A single-zone system—or bed farm—consists of several large,stacked beds or shelves within a singleroom (Figure 6). The substrate is filledinto these beds after Phase I, and thecrop remains in the one roomthroughout the process. Bulk pasteur-ization or tunnels are systems wherethe substrate is filled into “tractor-trailer”–type bins (called tunnels) withperforated floors and no covers on topof the compost (Figure 7). Phase IIand, occasionally, the next phase ofgrowing are carried out within thesetunnels. The substrate may then befilled into a tray, shelf, or even plasticgarbage bags for the remaining part ofthe process (Figure 8).

Figure 5. A tunnel used for Phase II and/or Phase III (spawn-growing) systems.

Figure 6. Single-zone, bed, or shelved farm. These shelves are aluminum; manyfarms have wooden bed boards.

Page 7: Agaricus Mushroom Growing

7

Phase II: Finishing theCompost

Phase II composting is the second stepof compost substrate preparation. Thefirst objective of Phase II is to pasteur-ize the composted substrate. Thecomposted substrate is pasteurized toreduce or eliminate the bad microbessuch as insects, other fungi, andbacteria. This is not a completesterilization but a selective killing ofpests that will compete for food ordirectly attack the mushroom. At thesame time, this process minimizes theloss of good microbes.

The second goal of Phase II is tocomplete the composting process.Completing the composting processmeans eliminating all remainingsimple soluble sugars and gaseous andsoluble ammonia created during PhaseI composting. Since ammonia is toxicto the mushroom mycelium, it mustbe converted to food the mushroomcan use. The good microbes in PhaseII convert toxic ammonia in solutionand amine (other readily availablenitrogen compounds) substances intoprotein—specific food for the mush-room. At the end of Phase II, volatileammonia (concentration more than0.05 percent) will inhibit mushroomspawn growth. Generally, ammoniaconcentrations above 0.10 percent canbe easily detected by a person and aretoxic to the spawn. Most of thisconversion of ammonia and carbohy-drates is accomplished by the growthof the microbes in the compost. Thesemicrobes are very efficient in usingPhase I composting products, such asammonia, as one of their main sourcesof food. The ammonia is incorporatedas mostly protein into their bodies orcells. Eventually the mushroom usesthese packets of nutrients as food.

Figure 8. Bag-growing system often uses substrate prepared in a bulkcomposting facilities.

Figure 7. Trays used for a multizone system, moving through a tray-filling line.

Page 8: Agaricus Mushroom Growing

8

Phase II objectives are possibly themost difficult procedures in growingmushrooms. Because of a compostingor other cultural problem, growerssometimes have to adjust Phase IIprograms. The Phase II process takesanywhere from 7 to 18 days, depend-ing on how the air and composttemperatures are managed to controlmicrobial activity.

During Phase II in standard bed ortray systems, compost temperaturesare brought down through all tem-perature ranges to ensure that all thedifferent species have a chance toconvert their specific source ofcarbohydrates. The compostedsubstrate throughout Phase II shouldappear to have moderate “firefang”—aterm referring to the white-fleckingmicrobial growth pattern of thethermophilic microorganism (Figure 9).

Pasteurization (peak heat, boost)should be completed toward the startof Phase II. Effective pasteurizationwill eradicate harmful bacteria,nematodes, insects, and fungi. Ingeneral, air and composted substratetemperatures should be raised togetherto 140ºF (60ºC) for at least 2 hours.Growers make several compromises tothis range, but it is a time-temperaturerelationship.

The good microbes grow best attemperatures from 115ºF to 140ºF;the more ammonia-utilizing microbesgrow best in the temperature range of120–128ºF (47–49ºC). The longerthe microbes in the compostedsubstrate remain in this optimumrange with all the critical growthrequirements available, the faster theammonia will be converted. Under-standing how these microbes growand work in composted substrateshould make the management ofPhase II a little easier. The process of

going through this temperature rangewill produce the most protein or themaximum amount of food for themushroom. A good rule of thumb isnot to drop the composted substratetemperature more than 5ºF per 24hours, which maintains the compostsubstrate in the desired range forabout 4 or more days.

Near the completion of Phase II,growers check for ammonia in thecompost. The nose is usually the besttool. However, ammonia-testing kitsand strips are available to supplementthe nose test.

Figure 9. Handful of composted substrate showing the white-flecking (“firefang”)microbial growth.

Figure 10. Pure culture of mushroom mycelium growing on an agar plate.

Page 9: Agaricus Mushroom Growing

9

Spawn Maintenance

A desirable mycelial culture is pure—free of contaminants and of sectoringof other abnormalities. Contaminantsinclude other fungi, bacteria, orinsects growing on or infesting theculture media along with the desiredmycelial culture. When a culture isfirst obtained, it should be transferredseveral times to fresh media to checkfor any form of contamination(Figure 10).

Sectoring is any type of mycelialgrowth that differs in appearance,growth rate, color, or in any other wayfrom the typical appearance of a givenstrain. Sectoring is often observed as amore rapidly growing area near theleading edge of growth, exhibiting adifferent growth habit from the rest ofthe culture. Other abnormalities thatmight appear in a culture are fluffy,aerial mycelia, thick or rubberytextures, and color changes such asbrowning or darkening of the myce-lium. Sectors of other change invegetative growth could affect theproductivity of the culture. Therefore,recognizing and avoiding propagationof abnormal mycelia to agar andfurther spawn production is veryimportant.

There is no in vitro test to determine astock culture’s validity. A series ofcropping trials must be conducted onthe mycelial stock culture to deter-mine a culture line’s value. Mushroomyield, size, color, cap shape, and anyother desired quality or growth factorsare selected and then compared foreach culture line.

Many commercially prepared spawnstrains are available to commercial andnoncommercial growers. All commer-cially grown strains are pure culture ofedible, fresh mushrooms; some mayvary in texture and growing require-ments. Mushroom spawn is producedin several different strains or isolates.Hybrid White is a smooth-cap, high-yield, excellent processing strain.Hybrid Off-White has a cap that isslightly scaly on first break and is apreferred fresh-market strain, andBrown (Portabella, Crimini) producesa chocolate-brown, mature mushroomthat is fleshy and has a strong, matureflavor.

Spawn Production

The process of making spawn remainsmuch the same as Penn State professoremeritus Dr. Sinden first developed inthe 1930s. Grain is mixed with a littlecalcium carbonate, then cooked,sterilized, and cooled. Small pieces ofpure-culture mycelium are placed insmall batches on the grain. Once thesmall batch is fully colonized, it isused to inoculate several larger batchesof grain (Figure 11). This multiplyingof the inoculated grain continues untilthe commercial-size containers—usually plastic bags with breathablefilter patches—are inoculated. Duringthe colonization of each batch, thecontainers are shaken every few daysto distribute actively growing myceliaaround the bag or bottle. During theprocess, temperatures are maintainedat 74–76ºF (23–24ºC). Uniformity ofthe air circulating around the bags isimportant to ensure that all containersare kept within the desired tempera-ture range. Mycelium is sensitive andits fruiting mechanism can be easilydamaged at high temperatures.

Figure 11. Spawn grains used to seed the compost with mushroom mycelia.Spawn is cooked, sterilized, grain cooled, and inoculated with mushroommycelia.

Page 10: Agaricus Mushroom Growing

10

Spawning

On bed farms, spawn and supplementare broadcast over the surface of thesubstrate. Uniformity of this distribu-tion is critical to achieve even spawngrowth and temperatures. On tray orbulk farms, spawn is usually meteredinto the substrate during the mixingoperation. Spawning is the cleanestoperation performed on a mushroomfarm. All equipment, baskets, tools,and so forth should be thoroughlycleaned and disinfected before spawn-ing.

The amount of spawn used dependson the length of the spawn-growingperiod and compost fill weights. Theuse of more spawn will result in aquicker colonization and moreefficient use of substrate nutrients.Improved colonization of substratewill help ensure that the mushroommycelia will grow quicker than otherfungal competitors.

During the spawn-growing period,heat is generated and supplementalcooling is required. Substrate tempera-

tures should be maintained at 75–77ºF and relative humidity should behigh to minimize drying of thesubstrate surface. Under properconditions, the spawn will grow as adelicate network of mycelia through-out the substrate. The myceliumgrows in all directions from a spawngrain. Eventually mycelia fromdifferent spawn grains fuse together,making a spawned bed appear as awhite root-like network throughoutthe compost (Figure 12). As thespawn grows, it generates heat. If thecompost temperature increases toabove 80° or 85°F, depending on thecultivar, the heat may kill or damagethe mycelia, reducing crop yield and/or mushroom quality. The timeneeded for spawn to colonize thecompost depends on the spawningrate and its distribution, the compostmoisture and temperature, and thenature or quality of the compost. Acomplete spawn run usually requires14 to 21 days. The spawn-growingperiod is considered complete whenspawn has completely colonized thesubstrate and the metabolic heat surgeis subsiding.

Substrate Supplementa-tion

The compost has to provide themushroom mycelium with a smorgas-bord of food. Not only is lignin-humus complex and cellulose impor-tant, but protein, fat, and oils are alsoimportant. A good analogy is proteinserves as the mushroom’s “steak,”carbohydrates its “potatoes,” andlipids (fats and oils) its “butter.” Likepeople, mushrooms should eat abalance of all these food types. Themain source of “steak and butter” forthe mushroom is from Phase IImicrobes. The dead cells of thermo-philic fungi, bacteria, and actino-mycetes “firefang” are the packagesthat deliver protein and fat to themushroom (Figure 9). The addition ofdelayed-release supplements furtherenhances the protein and lipidcontent of the compost for themushroom. Many of these supple-ments consist of a high-protein oilmaterial, such as soybean meal,cornmeal, or feather meal, that hasbeen treated to delay the availability ofthe nutrient for the mushroom. If anuntreated supplement is added to thecompost at this time, it often becomesa “candy bar” to other microbes,weeds, or competitor molds. Thesemolds grow more rapidly than themushroom mycelium and can quicklycolonize the compost, competing withthe mushroom for nutrients. The oilsor lipids in these supplements are usedby the mushroom to stimulate thefruiting mechanism and increase yieldby having more mushrooms initiateand develop. Yields can be increasedfrom 0.25 to 1.5 lbs/sq ft of growingspace. In addition, mushroom sizemay also be improved in compostwith higher spawning-moisturecontent. However, in substrate that isnot selectively prepared, these nutri-ents become more available to com-

Figure 12. Handful of mushroom substrate showing fully colonized spawngrowth.

Page 11: Agaricus Mushroom Growing

11

petitor molds. Often, if a farm ishaving composting problems, notsupplementing until the problems arecorrected is more economical.

Casing

The only method of forcing mush-room mycelia to change from thevegetative phase to a reproductivestate is to apply a cover of a suitablematerial—called the casing layer—onthe surface of the spawned compost.The function of a casing layer is totrigger the mushrooms to switch froma vegetative growth to a reproductiveor fruiting growth. The mechanismthat initiates the spawn to changefrom vegetative to reproductivegrowth is unknown, though severaltheories have been presented. Thecasing also functions to supply andconserve moisture for the mushroomsand their rhizomorphs (thickermushroom mycelia) and acts totransport dissolved nutrients to themushrooms. Casing supports themushrooms and compensates forwater lost through evaporation andtranspiration. Rhizomorphs look likethick strings. They are formed whenthe very fine mycelia fuse together andgrow through the casing.Rhizomorphs are thought to carrywater and nutrients from the compostto the developing mushrooms (Figure13). Mushroom initials—primordia orpins—form on the rhizomorphs.Without rhizomorphs, there will beno mushrooms.

The mushroom industry uses variousmaterials to provide a suitable envi-ronment for fruit body formations.Presently, most mushroom growersuse sphagnum peat moss or agedsphagnum peat moss buffered withlimestone. Sphagnum peat is relativelyinexpensive and readily available toNorth American growers. Pasteurized

clay loam field soil; reclaimed,weathered, spent compost; and coirfibers are other materials used bygrowers.

Most sphagnum peat has a pH of 3.5to 4.5. A neutralizing agent—usuallycalcium limestone—is added to bringthe pH level up to 7.5. Processed,spent sugar beet lime or hydrated limecan be used. Due to its higher neutral-izing capability and its greater solubil-ity, only small amounts are required.

Soil, spent mushroom substrate, andcoir fibers should be pasteurized toeliminate any insects and pathogensthey may be carrying. However, peatmoss–based casing does not needpasteurization because it is inherentlyfree of mushroom disease spores andpests. Distributing the casing so thedepth and moisture are uniform overthe surface of the compost is impor-tant. Such uniformity allows spawnsto move into and through the casingat the same rate and, ultimately, formushrooms to develop at the same

time. Casing should be able to holdmoisture because moisture is essentialfor the development of a firm mush-room.

CAC or CI

Fully colonized spawn run substrate isused to introduce mycelia into thecasing layer. This is often used toimprove crop uniformity, crop cycling,mushroom quality, and yields (Figure14). Spawn run compost at casing(CAC) is used to inoculate the casingduring the mixing or application ofthe casing. CAC is now producedmuch like spawn—in aseptic condi-tions—by those who produce andsupply spawn to growers. This processis called casing inoculum (CI). Byadding the mycelia uniformlythroughout the casing, the spawngrowth into the casing is quicker andmore even. The time from casing toharvest is reduced by 5–7 days so thatthe rooms can be cycled faster or morebreaks can be harvested in the same

Figure 13. Spawn growth in the casing and its thicker rhizomorph growth.

Page 12: Agaricus Mushroom Growing

12

time. Mycelial growth is uniform onthe surface, which encourages themushrooms to form on the surface aswell. Therefore, they are cleaner.Yields are improved since the mush-room growth is uniform and cropmanagement is easier. In addition,more mushrooms are produced fromareas that may have less nutrition.

Managing the crop after casingrequires that the compost tempera-tures until flushing be held at spawn-growing temperatures. After flushing,compost temperatures are lowered andair temperature becomes the primarycontrol point. Throughout the periodfollowing casing, water must beapplied intermittently to raise themoisture level to field capacity beforethe mushroom pins form.

Watering or Irrigation

The moisture content of the casingoften determines the uniformity of thecasing depth. Casing, both by equip-ment and by hand, becomes moredifficult as the casing material in-creases in moisture (Figure 15). Peatmoss casing will lump up or adhere tothe different parts of the equipment,making the flow of the material uneven.

Knowing when, how, and how muchwater to apply to casing is an art formthat readily separates experiencedgrowers from beginners. Watering thecrop is the most delicate operation inmushroom growing. Although eachgrower may have his or her ownpreference, no specific casing-manage-ment practice and casing material areuniversally accepted. Despite so muchdiversity, many growers are still able toharvest good crops with good fresh-market quality.

Figure 14. Difference in time when CAC or CI is added tothe casing. The two figures on the left and the two on theright show the difference in spawn growth over time intothe casing.

Although much has been writtenabout when and how much water toapply at certain stages in the crop’sdevelopment, most growers rely ontheir ability to “read” the crop anddetermine how the mushrooms lookfrom day to day. Water constantlymoves throughout the croppingperiod: water is lost through evapora-tion and transpiration, and themushroom takes up water into itscells; water is replaced when wateringthe casing layer. The increase in theweight of the mushroom frompinning to maturing is related to therapid uptake of water from the casingand compost. The mushroom doublesin size 2 days before harvest, puttingmore strain on the pipe system in thecompost and casing. As the mush-room matures during a flush, itsweight gain is attributed to theaccumulation of nutrients and waterfrom the substrate.

Figure 15. Most watering is done by hand, although newerfarms use hand-propelled watering trees.

3 days 3 days

11 days 5-7 daysCompost

Mycelium

Casting

Not CAC’d CAC’d

Page 13: Agaricus Mushroom Growing

13

Pinning

Mushroom initials develop afterrhizomorphs have formed in thecasing. The initials are extremely smallbut can be seen as clumps on arhizomorph. As these structures grow

and expand, they are called primordiaor pins (Figure 16). Mushroom pinscontinue to grow larger through a pre-button stage and ultimately enlarge tomature mushrooms. Mushroomharvesting begins 15–21 days aftercasing, which is normally 10–12 daysafter flushing and 7–8 weeks after

composting started. The culturalpractices used during pin develop-ment and cropping include themanagement of air and composttemperatures and CO

2 content of

room air, and is often dependent onthe strain and number of pins thegrower wishes to form and develop.

Figure 16. The developmental stages of the fruiting process.

Mycelium Initials—Clumping

Pin—Primordia Pea-Sized Pin

Pre-Button

Page 14: Agaricus Mushroom Growing

14

Air-handling systems regulate theamount of fresh air entering the roomand temperatures within the room.Ventilation requirements depend onthe amount of mushrooms to begrown on the beds, heat, and CO

2

production, which increases withtemperature. Uniform air movementand circulation is important toprevent stale air with high CO

2 levels

from building up around the mush-rooms, which lowers fresh quality. Airtemperature is maintained in a rangeof 60–66ºF (15–17ºC); CO

2 levels

range from 1,000 to 2,500 ppm (1–2.5 percent) during the pinning andcropping stages. The most criticalstage of the mushroom’s developmentfor fresh quality and yield improve-ment is during the Rapidly Expanding

Stage (RES), when the mushroomdoubles in size every 24 hours (Figure17). This expansion stage depends ontemperature, moisture of the compost,and casing. The environment inside aproduction room determines the rateof transpiration, which aids in theflow of nutrients and moisture intothe mushrooms.

Mushroom size is dependent on thenumber of pins that develop for abreak or flush and by how the crop isprepared and managed. Portabellamushroom growers have learned tomanage the pin set to achieve enoughpins for good yield, yet, more impor-tant, to attain the right amount ofpins to produce the large maturemushrooms for the Portabella market.

Harvesting

Mushrooms are harvested over a 2–4-day period in a 7–10-day cycle calledflushes or breaks. When maturemushrooms are picked, an inhibitor tomushroom development is removedand the next flush moves towardmaturity. Timing of the breaks orflushes is managed by control of thewatering, CO

2, and temperatures. The

first two flushes account for themajority of the total yield, with thesubsequent flushes tapering off torelatively low levels of production.Mushrooms are harvested by handand are picked at a time before the capbecomes soft, indicating the mush-room is past prime fresh-qualitypotential (Figure 18). Harvesting ratesdepend mainly on the amount of cropon the beds and size of the mush-rooms. Rates vary from 30 to 80 lbs/hour.

Some consumers seem to preferclosed, tight mushrooms, while othersprefer stronger-flavored, more mature,open-cap mushrooms. Mushroommaturity is evaluated by how open theveil is, not by its size. Mature mush-rooms are both large and small,although both farmers and consumersfavor medium to large mushrooms.Growers harvest just three to fourbreaks per crop—a shorter harvestingtime allows more crops to be pro-duced in a year and helps to preventdisease and insect problems.

Diseased, malformed, and fly-dam-aged mushrooms are consideredsecond-grade and are discarded.Diseased mushrooms should not betouched. Diseased tissue should betreated with registered chemicals, bio-pesticides, or common disinfectantmaterials such as salt or alcohol.

Figure 17. Mature mushrooms ready for harvesting.

Page 15: Agaricus Mushroom Growing

15

While mushroom yields vary, theaverage yield for the United States in2001 was about 5.75 lbs/sq ft. Withimproving technology, such as air-handling systems, heavier compost dryweights, supplementation, andimproved strains, growers haveachieved yields higher than 8.0 lbs./sq.ft. However, these high yields are onlyachieved on farms that are properlyequipped and have very experiencedgrowers.

Figure 18. Mushrooms for the fresh market are only harvested by hand. Thestem with some of the “root” attached is trimmed before the mushroom isplaced in a market container.

Post-Crop Pasteurizationand Spent MushroomSubstrate (SMS)

When a house becomes unproductive,the crop is usually terminated. Beforeremoving the spent substrate from themushroom house, the grower “pas-teurizes” it with steam to kill anydiseases, pests or other biologicalactivity that could interfere with a

neighboring house or subsequentcrop. The steaming-off procedure isaccomplished by maintaining acompost temperature of 140–150ºF(60–70ºC) for anywhere from 8 to 24hours. The spent compost should beremoved from the farm to reduce thechances of contaminating the subse-quent mushroom crops at the farm(Figure 19).

Spent mushroom substrate (SMS) isthe soil-like material remaining after acrop of mushrooms has been har-vested. Spent substrate is high inorganic matter, making it desirable foruse as a soil amendment or soilconditioner. Sometimes this materialis called spent mushroom compost.SMS still has some nutrients availablefor the mushroom. However, replac-ing the substrate and starting a newcrop is more economical. Users shouldconsider spent substrate clean of weedseeds and insects.

The typical composition of SMS freshfrom a mushroom house will varyslightly. Since raw materials and othercultural practices change, each load offresh spent substrate has a slightlydifferent element and mineral analysis.Sometimes fresh substrate is placed infields for at least one winter seasonand then marketed as “weathered”mushroom soil. This aged material hasslightly different characteristicsbecause the microbial activity in thefield will change the composition andtexture. The salt content rapidlydecreases during the weathering orcomposting.

Spent mushroom substrate has manyappropriate uses. SMS is excellent tospread on top of newly seeded lawnsbecause it will provide cover againstbirds eating the seeds and will holdwater in the soil while the seedsgerminate. Since some plants andgarden vegetables are sensitive to high

Figure 19. SMS being emptied from a mushroom farm.

Page 16: Agaricus Mushroom Growing

salt content in soils, avoid using freshspent substrate around those plants.You may use spent substrate weath-ered for 6 months or longer in allgardens and with most plants. Ob-taining spent substrate in the fall orwinter and allowing it to weather willmake it ready for use in a garden thefollowing spring. SMS can be appliedas mulch in small amounts on turf allyear-round. Spent substrate is a choiceingredient for companies that makepotting mixtures sold in supermarketsor garden centers. These companiesuse spent substrate when they need amaterial to enhance the structure of asoil.

Related Readings

Atkins, Fred C. 1974. Guide toMushroom Growing. London: Faberand Faber Ltd.

Blui-n, H. 1977. The MushroomIndustry in Ontario. Toronto, Ontario:Economic Branch, Ontario Ministryof Agriculture and Food.

Chang, S. T. and W. A. Hayes. 1978.The Biology and Cultivation of EdibleMushrooms. New York: AcademicPress.

Lambert, L. F. 1958. Practical andScientific Mushroom Culture.Coatesville, Pa.: L. F. Lambert, Inc.

Penn State Handbook for CommercialMushroom Growers. 1983.

Kligman, Albert M. 1950. Handbookof Mushroom Culture. Kennett Square,Pa.: J. B. Swayne.

Vedder, P. J. C. 1978. Modern Mush-room Growing. Madisonville, Tex.:Pitman Press.

Wuest, P. J., M. D. Duffy, and D. J.Royse. 1985. Six Steps to MushroomGrowing. The Pennsylvania StateUniversity Extension Bulletin, SpecialCircular 268.

Prepared by David M. Beyer, associateprofessor and mushroom extensionspecialist.

Visit Penn State’s College of Agricultural Sciences onthe Web: www.cas.psu.edu

Penn State College of Agricultural Sciences research,extension, and resident education programs arefunded in part by Pennsylvania counties, theCommonwealth of Pennsylvania, and the U.S.Department of Agriculture.

This publication is available from the PublicationsDistribution Center, The Pennsylvania StateUniversity, 112 Agricultural AdministrationBuilding, University Park, PA 16802. For informa-tion telephone 814-865-6713.

Issued in furtherance of Cooperative ExtensionWork, Acts of Congress May 8 and June 30, 1914,in cooperation with the U.S. Department ofAgriculture and the Pennsylvania Legislature. T. R.Alter, Director of Cooperative Extension, ThePennsylvania State University.

This publication is available in alternativemedia on request.

The Pennsylvania State University is committed tothe policy that all persons shall have equal access toprograms, facilities, admission, and employmentwithout regard to personal characteristics not relatedto ability, performance, or qualifications asdetermined by University policy or by state orfederal authorities. It is the policy of the Universityto maintain an academic and work environment freeof discrimination, including harassment. ThePennsylvania State University prohibits discrimina-tion and harassment against any person because ofage, ancestry, color, disability or handicap, nationalorigin, race, religious creed, sex, sexual orientation,or veteran status. Discrimination or harassmentagainst faculty, staff, or students will not be toleratedat The Pennsylvania State University. Direct allinquiries regarding the nondiscrimination policy tothe Affirmative Action Director, The PennsylvaniaState University, 328 Boucke Building, UniversityPark, PA 16802-5901, Tel 814-865-4700/V, 814-863-1150/TTY.

© The Pennsylvania State University 2003

CAT UL210 5M8/03ps4599

Produced by Information and CommunicationTechnologies in the College of Agricultural Sciences