SVegetable Crops MR 71-3
rch, 1971 HUME LIBRARY
7 -3 Compiled by JUL 11 1972
James M. Stephens
Assistant Vegetable Crops Specialis iFA.S.- Univ. of Florida
Florida Cooperative Extension Service, IFA-
This information on mushrooms has been compiled in response to the
many requests from Florida citizens interested in mushroom growing. Since
mushroom growing is not a significant industry in Florida, very little
local information is available.
The following reports are reprinted here for the study of the reader.
In some cases, copies may still be available from the authors of each report.
1. "Mushroom Growing in Florida," by Erdman West, University of
2. "Mushroom Growing in the United States," U.S.D.A. Farmers
3. "Growing Mushrooms," by W. L. Sims, University of California.
4. "No Sunshine For This Crop," by V. K. Thomas, American Vegetable
5. "Milestones in Mushrooms," American Mushroom Institute.
6. "Production of Mushrooms From Sawdust," by S. S. Block, G. Tsao,
and L. Han, University of Florida.
7. "Some Common Edible and Poisonous Mushrooms," by H. M. Fitzpatrick
and W. W. Ray, Cornell University.
8. "Physical Specifications of Mushroom Processing Plants," by C. W.
Coale, Jr., W. T. Butz, and G. D. Kuhn, Pennsylvania State
9. "Casing Soil Treatment in Commercial Mushroom Production," by L. C.
Schisler and P. J. Wuest, Pennsylvania State University.
10. "Watering and Ventilating From Casing Through Cropping in Commercial
Mushroom Production," by L. C. Schisler and P. J. Wuest, Pennsyl-
vania State University.
11. "Harvesting the Commercial Mushroom Crop," by L. C. Schisler and
P. J. Wuest, Pennsylvania State University.
12. Mushroom Extracts.
13. Mushroom Spawn Sources.
S MUSRHOOM GROWING IN FLORIDA
Plant Pathology Mimeo Report 54-1
Erdman West ,
Wild mushrooms and toadstools are very common in Florida at all seasons
of the year. They are especially abundant-during the warm humid rainy season.
Some are edible, some unwholesome and a few are deadly poisonous. Distinguish-
ing the edible kinds from the others requires'special training and can be done
safely only by an expert. No popular books on the subject are available for
our Florida plants.
The abundance of wild forms inspires many people to want to grow
cultivated mushrooms in Florida. The requirements for the successful
accomplishment of this wish are very stringent. A number of attempts have
been made in Florida to grow cultivated mushrooms for personal use and on
a commercial scale. Very few of these have been successful for several
different reasons. First of all, the materials necessary to make the
compost on which the mushrooms are grown are expensive to obtain in Florida.
Usually these must be'shipped in from other states. Second, it is impossible
to maintain the necessary moisture and temperature conditions without using
air conditioning equipme'ht which adds greatly,.to the expenses. Finally, our
climatic conditions are such that fungus diseases and insect pests attack
wild mushrooms 12 months in the year and these pests must be combatted
continually on the cultivated mushrooms.
Citizens are advised not to attempt to raise mushrooms until they
have carefully investigated the cost of the necessary buildings and equip-
ment as well as the requirements of the crop in regard to compost, tempera-
tures, humidity, etc. Ample financial resources should be available.
MUSHROOM GROWING IN THE UNITED STATES
U.S.D.A. Farmers Bulletin 1875
t . April, 1963
Edmund B. Lambert
Individuals seeking inforrat~fon on' mushroom growing are frequently
misled into believing that it is an occupation offering unusual opportunities
for profit with little experience and a small capital investment. -Often a
beginner has spent a considerable part of his savings on a mushroom-growing
venture before realizing that he is entering a well-established and competi-
tive field with a low margin of profit.
The purpose of this bulletin is to give prospective growers information
on the requirements for commercial mushroom growing and to point out the
obstacles beginners are likely to encounter. Cultural practices are described
briefly to give thenovice some idea of the complexity of mushroom growing. A
short discussion of amateur mushroom growing at home is included since many
inquiries are made by garden enthusiasts who would like to grow mushrooms in
the winter as a continuation of their summer gardening activities.
The beginner will almost certainly be disappointed if he expects to
make easy profits during the years he is learning to grow mushrooms. Con-
siderable physical labor is required for the preparation of mushroom beds,
perhaps more than in any other horticultural venture. To obtain profitable
yields the grower must have adequate facilities, a thorough knowledge of the
principles of mushroom growing, and a skill that can be developed only
through long experience.
The minimum size of a mushroom-growing establishment required to
make a livelihood for a family is one with about 20,000 square feet of
bed space. In 1954 the cost of building and equipping a plant of this
size was approximately $30,000. Additional working capital of about $5,000
is required to pay for the manure, spawn, and labor needed to prepare the
beds before salable mushrooms are obtained.
The Mushroom Industry
Mushroom culture is not new. It was practiced in France and England
for many years before it was introduced into the United States in the
latter part of the 19th century. The first mushroom-growing center in
this country was in the vicinity of New York City, extending out onto
Long Island. About 1890, greenhouse operators near Kennett Square, Pa.,
started to grow mushrooms in the unused spaces under the greenhouse
benches. Soon many farmers in the vicinity were growing mushrooms in
idle space in barns, sheds, and cellars; and by the turn of the century
special sheds were being constructed for the sole purpose of growing
mushrooms. A large part of the industry still is concentrated in
Pennsylvania, Delaware, and New York. However, climatic and soil con-
ditions permit the commercial culture of mushrooms in all States except
those of the deep South, and now growers are located in the vicinity of
all the large cities in the northern States. The comparatively high cost
of artificial refrigeration has, with a few exceptions, prevented the
development of large establishments in the southern States.
Mushroom culture has made rapid strides in the United States during
the past quarter century, both in the improvement of cultural methods and
in total production. At first, crop failures were frequent and an average
production of one-half pound per square foot was considered a good yield.
Following the introduction in 1918 of pure-culture spawn grown from
selected spores, and the practice of pasteurizing the beds before planting
the spawn, the average yield soon increased to 1 pound per square foot and
is now (1960) between 1 and 2 pounds per square foot per crop.
According to estimates made by representatives of the industry over
30,000,000 square feet of bed space was planted to mushrooms in 1960. The
total annual production has been estimated at 125,000,000 pounds. Between
15,000 and 20,000 workers are engaged in growing and canning mushrooms.
Several million dollars are spent annually for horse manure and materials for
making artificial compost. Most of the growers use mechanical equipment such
as trucks, tractors, conveyors, and loaders. The total capital worth of all
businesses depending on mushroom growing has been estimated at well over
Nature of the Mushroom and Its Nutritional Value
Only one type of mushroom is cultivated in the United States--a horti-
cultural adaptation of the common field mushroom. The portion of the mushroom
appearing above ground is the edible mushroom of commerce. When mature, it
produces and liberates spores, microscopic reproductive bodies similar in
function to seeds. All parts of the mushroom are;edible. The flesh. 6f the
stem is nearly.as soft as that of the cap and there.is no protective covering
such as the bark on the stems of higher plants or the:waxy 1"bloom" on some
fruits and leaves. The rootlike part of the mushroom plant grows extensively
underground before the edible portion is formed. It consists of a white
cottony mold which permeates partly decomposed organic matter to seek nutrients
in a manner similar to the way roots of higher plants permeate the soil. A
fundamental difference:between mushrooms and green plants is ,that the latter
can mah'facture:'their own carbohydrate food, whereas mushrq9ms cannot. Mush-
rooms are grown in organic compost containing carbohydratess p,.add.ition to
the minerals and nitrogen required by green plants. They .cnnot be grown in
a liquid medium (hydroponics), because the presence of carbohydrates in the
liquid will stimulate the growth of airborne contaminating molds which soon
crowd out the "mushroom mold."
Cultivated mushrooms have a place in the average American diet, not
only on the basis of their flavor, but also because of definite food values
which they possess. They contain much less protein than meat and fish, but
mushrooms compare favorably with most fresh vegetables in protein content
and are good sources of vitamins and of minerals .such as iron and copper.
Mushrooms are an excellent plant source of riboflavin and nicotinic acid
and a good source of pantothenic acid. They also contain appreciable amounts
of thiamin and biotin. These vitamins are well retained during cooking and
in canned, dehydrated, and frozen mushrooms.
Sites for Mushroom Growing
The climate in the United States is not suitable for the commercial
production of mushrooms out of doors. To obtain satisfactory yields they
must be grown in enclosed rooms arranged to permit the regulation of tempera-
ture, humidity, and ventilation. Various types of structures have been used
for growing mushrooms but the type which has proved most satisfactory is a
long, narrow building containing 10 or 12 shelf beds. These houses are 65
feet long, 20 feet wide, and about 15 feet high. The beds are arranged in
2 tiers,.5 or 6. beds high, and are usually 5 feet wide. A house of this
size contains about 3,600 square feet of bed space and is called a "single
house." Frequently, two such units are built together under a single roof,
and in this case are termed a "double house." A moderate-size mushroom
establishment consists of at least three such double houses. They are
usually placed on a hillside in such manner that the beds may.be.filled from'
the higher part of the site without special equipment for elevating the manure.
Since 1935, a few growers have adopted a system of culture that makes
use of small movable trays of compost instead of fixed beds. With this
system, sometimes called the "two zone" system, two separate series of rooms
are needed, one for pasteurizing the manure and growing "spawn" in the beds,
and the other for growing the mushrooms. The surface of the compost in the
trays is usually covered with a thin layer of soil at the time the trays are
transported from the spawning rooms to the growing rooms. This soil covering,
is called the "casing" and is used in both bed and tray systems of culture.
The tray system is especially well adapted to situations in which large
areas of suitable space are available in abandoned buildings, caves, mines,
et cetera, that can be cheaply modified to provide year-round conditions
favorable for the growing phase of mushroom culture, but which would be
difficult or impracticable to heat to pasteurizing temperatures. In such
situations comparatively small buildings are constructed to provide the
necessary pasteurizing rooms. In favorable situations the cost of building
these small pasteurizing rooms and adapting the available growing space for
culture may be considerably less than the cost of building an equivalent
area of standard mushroom houses. This advantage has enabled a few growers
using underground limestone or gypsum mines to develop very large installa-
tions. The two largest mushroom plants in the United States, one on the
Hudson River near Albany and the other near Butler, Pa., are installations
of this type. These plants produce several tons of mushrooms per day.
Preparation of Compost
Mushroom growers traditionally have used composted horse manure to
fill their beds, but in recent years a satisfactory synthetic compost,
prepared from a mixture of corn cobs and hay supplemented with fertilizer
containing nitrogen, phosphorus, and potash, has been used.
Horse manure is obtained principally from racing stables and riding
stables. Growers usually mix manure from different sources so as to obtain
a more or less standard mixture with a medium content of straw. When the
manure is received in the spring or early summer it is usually stored in
large heaps like haystacks to retard decomposition until ready for use.
The first step in the composting of the manure for mushroom culture
is to place it in heaps 8 or 10 feet wide by approximately 7 feet high, and
as long as is convenient, meanwhile wetting it as thoroughly as possible.
Gypsum is added throughout.the heap as it is built at the rate of about 30
pounds per ton of manure. Two to four days after the heap has been estab-
lished it is broken up, wetted again, aerated, and mixed thoroughly by
passing it through a special "turning" or mixing machine. This procedure
is repeated three times at intervals of 4 or 5 days. At the end of this
time the compost is much more uniform in moisture than at first, and has
been partially broken down;by fermentation.
In some cases growers have found it advantageous to supplement very
strawy horse manure with material such as brewers' grain, cottonseed meal,
or poultry manure that is medium high in nitrogen content. Brewers' grain
is usually added to strawy manure at the rate of approximately 100 pounds
per ton of manure; one-third of this amount is applied during the second
turning, one-third during the third turning, and the remainder during the
fourth turning. Cottonseed meal is usually used at the rate of 60 pounds
per ton, and dried poultry manure at the rate of 150 pounds per ton.
Many growers in eastern Pennsylvania are using synthetic compost
made according to a procedure developed cooperatively by J. W. Sinden of
the Pennsylvania State University, the Boy-Ar-Dee Mushroom Company at Milton,
Pa., and the Butler Mushroom Company at West Winfield, Pa. The following is
approximately the list of materials required for making compost for filling
a double house: 15 tons of corn cobs, 7 tons of meadow hay, 4 tons of clover
or alfalfa hay, one-half ton of gypsum, 500 pounds of ammonium nitrate, 500
pounds of muriate of potash, I1 tons of dried brewers' grain or like amount
.*of dried poultry manure, and a total of 10,000 to 11,000 gallons of water to
' give the desired moisture content. Modifications of this formula are being
tried experimentally to improve crops, but the proportions as listed above
have consistently given good results.
This material is composted'in essentially the same manner as horse
manure except that it requires a great deal more water than horse manure
does throughout the composting process. Corn cobs and hay will hold more
water than horse manure does without being excessively wet. When the heap
is first made .the corn cobs and hay are placed alternately in layers about
4 inches thick and given all the water they will take without water running
out of the heaps. Two days later the mixture is passed through.a turning
machine and wet again with all the water it will take. Three or four days
later the pile is again turned with the machine and wet thoroughly.. The
chemicals are now added to the top of the pile and in another four days the
pile is turned again, mixing the chemicals and wetting the material as it
is turned. It is turned again in 4 or 5 days and made ready for filling
After the last turning the compost should be in long, narrow, well-
aerated heaps, not wider than about 8 feet. It should have a water content
between 70 and 75 percent. The beds are filled to a depth of 6.to 10 inches,
a ton of moist compost filling approximately 100 square feet of bed. When
all.of the beds are filled with compost the doors and ventilators are closed
and the temperature in the room is allowed to rise as a result of the heat
generated in the manure, assisted with live steam, until the temperature
in the compost is between 1350 and 1400 F. This temperature is maintained
until all odor of ammonia has left the compost and its pH value is 8.2 or
below. The beds are watered during pasteurizing so that they will contain
about 65 percent moisture at the end of the pasteurizing period. When the
pasteur.izing is completed, usually after 4 to 6 days, the room is ventilated
to bring the temperature down between 750 and 800 F. This temperature is
suitable for "spawning"--the period of growth that includes the planting
of the mushroom spawn and the development of the fungus in the compost
before the mushrooms appear. This prolonged pasteurizing period in the house
is an essential part of the composting procedure and, although there are
several modifications in the temperature sequence followed by different,
growers, all are agreed that some form of pasteurizing must be carried.out
to control harmful fungi, insects, and nematodes, and to obtain consistently
SThe propagating material 'sed by all growers for planting the-beds is
called spawn. It is usually prepared on one of three materials--grain, manure,
or tobacco stems. There are several well established spawn makers who have
mastered the intricate pure~culture technique necessary for preparing pro-
pagating material from the spores of the mushrooms. Nearly all growers
prefer to purchase spawn from these pure-culture spawn makers rather than
attempt to preparer it themselves.
Spawn is usually broadcast over the surface of the beds. The spawn
is allowed to grow in the .bed for about 7 days while the temperature is
held at approximately 70 :F. The bed temperature is then lowered to between
650 and 700 while the spawn continues to grow for an additional week or two.
At the end of this period the cottony growth of mushroomispawn will have
permeated most of the upper 3 inches of the bed. Some'ventilation is
provided during the growth of the spawn and the surface layer of manure is
watered lightly to retain-an appropriate moisture content of.about 65
percent throughout all of the compost in the bed.
After the spawn has "run" in the bed 2 or 3 weeks, a layer of about
an inch of "casing" soil is spread over the surface of the bed. The soil
should be a loam that is neither too sandy in texture nor too.:high in clay,
and neutral in reaction. If the soil to be used for casing islacid, it is
usually neutralized by adding ground limestone. This soil is kept moist
with very light watering until the mushrooms begin to form. The first
mushrooms will appear all over the surface of the bed about 3 weeks after
At the time mushrooms appear, the temperature is lowered to a chosen
*point between 500 and&650 F. If a slowly developing crop with a long harvest
season is desired, 'the temperature is held at about 500. If more rapid
development with a short harvest season is desired, the temperature is held
at about 620. Mushrooms will continue to develop for 2 or 3 months, depending
on the temperature. They usually appear in sudden outbreaks at intervals of
about a week. These outbreaks are called "flushes" or "breaks" and are
followed by periods with only a few mushrooms appearing on the bed. Usually
-additional water is applied to the surface of the bed at the time each
break is appearing. The soil moisture must be maintained at a rather high
level to obtain maximum crops.
DUring'the growthofthe nmul rooms the humidity of the air in the
mushroom house must be maintained above 70 percent to prevent drying out of
the mushroom caps. At the same time considerable ventilation must be supplied
to assure maximum yields. Usually it is advisable to give as much ventilation
as possible without interfering with temperature and humidity control, or
causing a cracking of the surface of the mushrooms.
There are many diseases and pests of mushrooms which tend to reduce the
yields and render the mushrooms unsalable. Frequently, these pests are the
cause of partial or complete crop failure. While the success of a commercial
grower depends largely on his ability to exclude or control these pests, they
are too numerous and the control measures too intricate to be discussed here.
More detailed information on all. phases of mushroom growing is
available in textbooks:"and other publications listed in amimeographed
paper entitled "Sources of Mushroom Spawn and Additional Information"
distributed by the Office of Information, U.S. Department of Agriculture,
Washington, D. C.
Harvesting and MarketFng
Mushrooms are "picked" just before the cap expands to expose the "gills.'
In this stage of growth they may range from 1 inch to 3 inches in diameter.
After the mushroom or clump of mushrooms has been picked, the remaining fleshy
mushroom tissue is carefully removed from the soil and the hole filled with
fresh soil. Large numbers of young "'button" mushrooms from one-eighth to
three-eighths inch in diameter die off after the larger mushrooms are removed,
even on normal beds, presumably because harvesting the large mushrooms breaks
many of the strands connecting the young mushrooms with their supply of
nutrients in the compost. With a little practice these dead or damaged
mushrooms are easily distinguished from healthy buttons and are removed from
the bed to prevent spread of decay. This job must be done:thoroughly at
frequent, intervals in order to assure maximum crops..
When the mushrooms are to be sold on the fresh market the stumps are
usually cut off at the time of picking and the mushrooms are sorted according
to size, freedom from blemishes, and certain other requirements. They are
packed in 7-ounce or 1-pound cartons, or in 3-pound baskets. In most large
cities they are sold by fruit and vegetable produce dealers. These merchants
receive the mushrooms on consignment, set the wholesale price in accordance
with supply and demand, and charge the grower a 10-percent commission for
their services... The daily wholesale price of fresh mushrooms is usually
quoted in the local newspapers.
In some localities the grower may have a choice between sending his
mushrooms to produce dealers, to canneries, or to soup makers. The demand
for canned mushrooms has increased in recent years until, at the present
time, most of the mushroom crop is sold in cans. One-third is marketed as
fresh mushrooms, one-third as canned mushrooms, and the remainder is pro-
cessed in soup. The sale of both canned mushrooms and mushroom soup has
played a very important part in the nationwide acceptance of mushrooms as
an everyday food product. National advertising of mushroom soup has once
and for all dispelled from the mind of the average housewife the unfounded
fear of mushroom poisoning. This product quickly won popularity since it
is a relatively inexpensive item of good quality. The processing industries
also serve as important and indispensable factors for stabilizing the price
of mushrooms in large production centers.
Drying and Freezing
Mushrooms can be successfully dried by placing them on wire trays one
layer deep and passing a rapid current of warm air over them. If the tempera-
ture of the mushrooms is raised to 1300 F. for a few hours during drying, all
insects Infesting the mushrooms will be killed. When thoroughly dry and free
from insects they will keep in good condition more than a year. If dried in
a vacuum while frozen, they retain full flavor. If exposed to moisture or
high humidity, they deteriorate rapidly as a result of enzymic changes or
the invasion of insects and decay organisms.
Over a. period of 25 years sporadic attempts have been made by large
Smshroom growers in the United.States to market the common cultivated variety
in a dried or:pocwdered,form.: For various reasons, such as extreme-shrinkage
in weight during drying--10 to I--and competition with the fresh or canned
Product, these commercial ventures in mushroom drying haveriot been found
profitable in this country. The dried mushrooms sold in the United States
(1955) are imported from Europe and the Orient. They are not the same kind
as are cultivated in :this country. Those from Europe are wild mushrooms
gathered from the fields and those from the Orient are of different kinds
cultivated by entirely different methods than those used in'the United States.
When mushrooms are quick frozen in the raw state they retain their
full flavor and attractiveness for only about a month. After this the
tissue turns black due to the action of oxydizing enzymes. On the other
hand, they will keep a long time in the frozen state if blanched by
steaming or boiling before freezing.
Costs and Returns
The mushroom grower encounters most of the economic difficulties
. that confront the producer of other perishable crops. Under present market
conditions (1961) there is no assurance that a grower will be able to raise
mushrooms at a profit.
Because yields are highly variable, the cost of producing a pound of
mushrooms is difficult to estimate. The most important items of cost are:
Interest on the investment, depreciation, manure or synthetic compost, soil,
spawn, labor for composting, filling, spawning, casing, picking and packing
for market, and emptying the beds.
The price differs from one locality to another and from one season
to another. It is usually beyond the grower's control. Because his product
is highly perishable, he must send it to market on the day it is harvested
and cannot ship it long distances. Warm spells in the early fall and late
spring may greatly increase the supply of mushrooms for several days at a
time by raising the temperature in mushroom houses. The temperature rise
is reflected in an increased rate of growth of the mushrooms and in the
production of a larger proportion of small mushrooms. In congested centers
of mushroom growing, this usually occurs in hundreds of mushroom houses at
the same time, and the grower often finds himself in the untenable position
..of producing the most mushrooms when the price is below the cost of pro-
Mushroom Growing at Home
The cost of the material and labor for mushrooms produced at home may
be slightly greater than the cost of mushrooms purchased at the local store;
however, mushroom culture at home offers a fascinating winter hobby, with a
reward of freshly picked mushrooms for family and friends.
Most amateurs will find it very difficult and disagreeable to prepare
a suitable mushroom compost from a small heap of manure. Without the facili-
ties of the commercial grower for pasteurizing, the compost prepared by an
amateur will frequently be unsuited for mushroom culture because of the
presence of harmful fungi, nematodes, and insect pests.
In recent years a few nurserymen and seedsmen have been offering for
sale trays containing mushroom compost especially prepared for home use,
which appear to be the solution to many of the problems of growing mushrooms
at home. It is recommended that the amateur grower purchase these prepared
trays instead of attempting to make his own mushroom compost. They are
prepared for the nurserymen and seedsmen by commercial mushroom growers who
are equipped to compost manure economically on a large scale, to pasteurize
the compost effectively, and grow spawn in the trays. Full directions for
growing mushrooms are furnished along with the trays. If the directions are
carefully followed, and if the trays are placed in a cool, damp location,
moderate yields can be expected, usually between one-half pound and a pound
per square foot of tray space.
Once the mushrooms begin to appear on the trays they will continue to
develop for about 60 days. As mushrooms do not need light for normal develop-
ment, they can be grown in a basement room or shed where it would be impossible
to grow green plants. Growing space must be available in which the temperature
can be maintained under 650 F., and the humidity of the air kept moderately
high. Some ventilation is necessary, but the number of air changes normally
occurring in the average cellar room will usually be sufficient for a few
square feet of mushroom bed.
William S. Sims
Many false ideas exist about mushroom growing. Many people think
mushrooms are easy to grow, require little "know how" and, bring high
profits. Actually, the opposite is true. The mushroom industry today is
highly specialized with many pitfalls for the beginner. Considerable
capital, experience, and "know how': are needed to operate successfully.
Description Many natural species of edible fungi are found in this
country. The most popular is the Agaricus campestris. A horticultural
adaptation of this species is used for commercial growing. From the grower's
viewpoint, there are two varieties--the white and the brown. The mushroom,
being a fungus, produces spores, not seeds. These, in turn, must be induced
to produce a threadlike mass called mycellus which, under the proper con-
ditions, develops edible mushrooms.
Capital Investment Several of our small commercial growers feel,that
the minimum size of a;mushroom-growing establishment required to make a liveli-
hood for a family is 10,000 to 15,000 square feet. The cost of the building,
equipment, and working capital. required can be estimated from this base.
The Mushroom House A typical mushroom house can be constructed of
wood or concrete blocks. It should have three tiers of beds with four beds
in each tier, making a total of twelve beds per house, giving a total bed.
surface of approximately 4,000 square feet. Beds are usually five to six
feet wide. Because light is unnecessary for growth, the houses need no
windows. Sawdust, rock wool, or some other comparable material may be used
for insulating the house. Vents are necessary to air and control temperatures
S "In preparing a mushroom house for a new crop it is necessary to,elimi-
nate insects or disease by filling the house with live steam or by using a:
chemical poison such as sodium cyanide.
S Composting Mushroom growers use horse manure, chicken manure, or a
combination of the two for composting material. Horse manure is the most
popular and is often secured from horse racing stables. It is purchased by
the yard. The mushrooms will be grown on this material. A synthetic com-
post made up of hay, chopped corn cobs and additional chemical ingredients
mdy also be used.
Whether manure or "synthetic" is used, the compost must go through a
conditioning process. It is usually placed in piles six feet wide and six
feet high on a concrete slab or floor. This material is wetted, aerated,
and mixed thoroughly by turning. This is repeated three or four times at
weekly intervals. In this manner the compost is broken down by the micro-
organisms present. Often it is necessary to spray the compost pile with an
insecticide to control flies.
Pasteurization After the last turning, the compost should have,,a
moisture content of approximately 70% on a dry weight basis. The beds are
filled to a depth of six inches with the composted material. When the beds
have been filled, the doors and ventilators are closed and the temperature
in the beds is allowed to rise to 135-1400 F. from the heat generated in the
manure. It generally takes three days to reach this temperature. If nec-
cessary, live steam is introduced into the beds to bring the temperature
to the desired degree. This high temperature is maintained for 24 hours
until all odor of ammonia has left the compost. Then the house is venti-
lated and the temperature in the beds permitted to drop to 75-800 F. The .:
entire pasteurizing process requires 10 to 12 days.
Spawning Propagating material used by growers for planting beds Is
called spawn. In California the spawn carrier is usually manure or grain.
This material is purchased from a supply house at a cost of 60-65 per pound.
Several well-established spawn makers have mastered the intricate pure-culture
technique necessary for preparing propagating material from the spore of
When manure spawn is used, it is planted two inches below the surface
of the bed at intervals of about 12 inches throughout the bed area. Grain
spawn is usually broadcast over the surface of the beds. One pound of spawn
is used for approximately 50 square feet of bed. A spawning temperature of
72-750 F. is maintained. Beds must not be permitted to dry out.
Casing Manure spawn requires three to four weeks for the mycelium
to grow through the compost. Grain spawn takes 10 to 14 days. The beds
are then made ready for "casing." Mycellum will not develop into the fruiting
stage and produce mushrooms until a thin layer of soil has been spread over
the surface of the bed. Casing soil is usually a loam or peat, or a mixture
of the two.
Casing soil must be free of nematodes. Before using, the soil is
heated to a temperature of 1400 F. by means of live steam or is treated with
some nematicide to insure freedom from nematodes and soil diseases. If the
soil is acid, it is also neutralized by adding ground limestone (CaC03) and
mixing with the soil. After beds have been cased, the soil is kept moist
with very light watering until mushrooms begin to form.
Production The first mushrooms will appear over the surface of the
bed three to four weeks after casing. After the mushrooms begin to show,
the temperature is lowered to 600 F. The lower temperature improves mush-
room growth and also discourages diseases and insects. Mushrooms come in
sudden outbreaks at intervals of about one week. These outbreaks are called
"flushes" or "breaks." The greatest production is obtained from the first
two breaks but five to seven distinct breaks will emerge over a period of
two or three months depending on the temperature. Usually water is applied
to the surface of the bed at the time each break is appearing. During the
growing period the humidity of the air must be maintained at 70-80% to
prevent the mushroom caps drying out.
An average yield is one and one-half pounds of mushrooms per square
foot. However, two and three pounds per square foot may be obtained.
Harvesting and Marketing Mushrooms are picked just before the cap
expands to expose the "gills." In this stage of growth they may range from
one inch to three inches in diameter. After the mushroom or clump of mush-
rooms has been picked, the remaining fleshy mushroom tissue is carefully
removed and the hole filled with fresh soil.
Mushrooms are usually graded by size--small and large. The small
sizes are generally sold in 4-6-8 ounce paper cups and large sizes in pound
cartons. Mushrooms may be sold on the fresh market or to the canneries.
S* * .13- ; / .
Pests and Diseases The mushroom growing industry has its problems,
with. pests and diseases. White mold (mycogone perniciosa) often called
"bubbles" may appear at any time after cropping begins. Other diseases ;'(;
that may occur are verticillium, Dactylium dendroides, brown block or bac-
terial spot, damping off, truffle and white plaster mold.
Pests that may cause trouble are woodlice, millepedes, springtails,
mites, gnats, and phorld flies. For additional information and the latest
control measures please consult your local farm advisor's office.
For the Amateur In recent years a few nurserymen and seedsmen have
been offering for sale trays containing mushroom compost, especially pre-
pared for home use. The amateur might find it economical and convenient
to purchase these. They are prepared for the nurserymen and seedsmen by,
commercial mushroom-growers who are equipped to compost manure economically
in a large scale, to pasteurize the compost effectively, and grow spawn in
the trays. Full directions for growing mushrooms are furnished with the
NO SUNSHINE FOR THIS CROP
"' American Vegetable Grower
V. K. Thomas
Agriculture is something of a paradox in Chester County, Pennsylvania.
Production is measured in pounds per square foot rather than in tons per acre;
crops are planted in autumn and harvested in winter and spring; darkness
rather than in sunlight is desirable, and, to produce a good crop, low
temperatures, instead of summer heat, are an absolute necessity. That's.
because southern Chester County is the world center of mushroom production.
Although the Kennett Square area of Chester County represents the
greatest concentration of the industry, mushrooms are being grown elsewhere
in Pennsylvania and in many other parts of the United States.
Profitable production of mushrooms requires heavy labor, constant
attention to maintenance of favorable conditions, and eternal vigilance
against the inroads of insects and disease.
The mushroom, being a fungus, produces spores, not seeds. These, in
turn, must be induced to produce a threadlike mass called mycelium or spawn,
which, under the proper conditions, develops edible mushrooms.
The early steps are called "spawn making" and are carried on in a
laboratory under conditions as sterile as a hospital operating room.
Before getting his spawn supply, the grower must prepare his houses.
A standard mushroom house, usually built of concrete blocks, is 60 by 20
feet and contains two tiers of beds with an alley between. Each tier is
six beds high, giving a total bed surface of approximately 4,000 square
feet. Most houses are now built as "doubles", that is, each house iS wide
enough for four tiers of beds instead of two. Because light is unnecessary
for growth, the houses are windowless.
The first step in preparing a mushroom house for a new crop is
steaming to eradicate contamination by insects or disease from the previous
crop. This is done by filling:the house withlive steam from a boiler.
A traveler in the mushroom:growing area during midsummer sees huge
piles of horse'manure or hay and corn cobs on concrete wharfs outside the
mushroom houses. These are the ingredients on which the mushrooms will be
grown. In the early years, horse manure was used almost exclusively for
compost. Since World War II, more and more growers are adopting what is
known in the industry as "synthetic compost," which is made up of hay,
chopped corn cobs and additional chemical ingredients in standard proportions.
Whether manure or "synthetic" is used, the compost must go through a
preparative process on the wharf during which it is turned several times,
either by hand or mechanical turner, and water added. in this way, it is
broken down by the chemical organisms present.
After the compost has been placed on the beds, it must go through a
pasteurization period.. This ,Is known as the "sweating out" process when the
house is tightly closed. The heat generated by the bacterial action in the
compost, in combination with moisture, boosts the temperature.
A uniform compost temperature of 1400 F. is considered sufficient to
kill the pests and molds which could injure the mushroom crop. To be certain
of attaniing this temperature, artificial heat is often added to the compost
heat as it approaches its "peak", and the optimum temperature is maintained
for 24 hours. The entire:pasteurization process requires about a week.
'When pasteurization is completed, the house is allowed to cool to
about 750 F. before the spawn is planted. Planting is done by broadcasting
the inoculated grain or other spawn carrier on the beds and covering with
compost. From these spots, the mycelium grows through the compost in
During this "spawn running" period, the temperature must be main-
tained at not more than 750 F., and beds must not be allowed to dry out.
Three to four weeks are required for the mycelium to grow through
the compost. The beds are then ready for "casing." While the mycellum
will grow in the compost, it will not develop into the fruiting stage and
produce mushrooms until a thin layer of soil has been placed on top of the
Since the mushrooms derive no nutrient from the soil, the physical
characteristics of good casing soil are more important than its chemical
composition. It must be of a consistency that will hold water without
becoming waterlogged and will not puddle or "cake" on the beds. Growers
consider that top soil meets these requirements better than subsoil. This
makes it necessary constantly to find new areas from which the top soil can
be removed, or to carry on a long-range program of rebuilding the top soil
from stripped areas.
i ,15, ... .
The soil's degree of acidity is a matter of importance. Casing soil
should test between 5.5 and 8.0 on the pH scale.
One of the most serious causes of crop failure has been found in recent
years to be due to hordes of certain species of nematodes in the casing soil.
These are present in all soils, and the most practical means of control thus
far has been that of heating the soil to a temperature of 1400 F. by means of
live steam. The soil as it comes from the field may also contain certain
insect pests as well as the organisms which cause mushroom diseases known as
"bubbles", Verticillium "spot", "truffles", and "mat" disease.
After sterilization has been completed, the soil is stored in a bin
or on a concrete wharf and covered with canvas or plastic to prevent recon-
When the beds are ready for "casing", about one inch of soil is placed
on the surface and leveled off. Again, there must be constant attention to
watering, temperature, and ventilation.
After the mushrooms begin to appear--about three weeks after casing--
the temperature must be kept at no more than 700 F. and preferably between
500 and 650 F. The lower temperatures improved mushroom growth and also
discourage diseases and insects. Mushroom growers, therefore, greet with
apprehension the suddenly warm days of early spring.
Mushrooms appear in somewhat rhythmic cycles called "breaks''. The
greatest production is obtained from'the first two breaks, but beds properly
adjusted for moisture and temperature will continue to produce mushrooms for
about three months. While average production in 1940 was only a pound per
square foot of bed space, yields of two and one-half to three pounds are
more common today.
In the Kennett Square area, growers usually grow two crops a year,
filling their houses in September for the first crop, and completing the
second crop with the advent of warm weather.
MILESTONES IN MUSHROOMS
The Versatile Vegetable '-
SThe American Mushroom Institute
'Post Office Box 373
Kennett Square, Pennsylvania
Mushrooms, the inexpensive luxury, add variety to menus, a lilt to
recipes, flavor to all foods, and mushrooms are low in calories...only 66
calories to a whole pound. Mushrooms make ordinary soups and sauces exciting,
turn meat, chicken, fish servings into gourmet delights. Mushrooms are for
your main dish variations. Eat mushrooms raw in salads and for dips and dunkF
Vary vegetables with sauteed mushrooms.
Food Values Mushrooms have long been recognized by nutritionists as
an Important food. In its National Food Guide the U. S. Department of Agri-
culture lists mushrooms In Group Three of its seven basic food groups. One
appealing thing about mushrooms is their low calorie content; less than 66
calories to the pound. They have a relatively high phosphorous content and
top many vegetables in riboflavin, niacin and calcium. They also contain
other B vitamins, and iron and copper.
Versatility as a Food No other vegetable can be served in so many
unusual ways. Mushrooms are delicious raw, or sauteed, or simmered or
pickled. They may be canned, frozen or dried. Mushrooms are new and
different--raw for cocktails and delightful in salads. Mushroom soup is
elegant and nourishing. Chicken and fish and eggs and meats are always
complemented when mushrooms are added. Plain vegetables forget to be routine
when fresh mushrooms or canned ones are sauteed and added. Mushrooms with a
touch of wine and sweet or sour cream, served on toast, suddenly becomes
company fare. Added to omelettes, casseroles, grilled servings, to rice,
pastas, mushrooms are still individual and the star of any act, when the show
Production and Sales Mushroom in Decade. So rapidly has the mushroom
industry grown that in Pennsylvania alone the annual mushroom crop provides
more farm income than the state's entire fruit crop or the state's entire
Production and sales have risen from 75 million to 170 million
pounds in the past ten years, one of the fastest growth rates in the nation's
Where Grown and How The heart of the American mushroom industry is
in Pennsylvania. Two thirds of the commercially cultivated mushrooms are
grown in this state. Kennett Square, Pennsylvania, where our American Mush-
room Institute is located is called the Mushroom Capital of the U.S.A.
And the rest of the production? Elsewhere in Pennsylvania, as well as In other
parts of the United States, California and the Pacific Northwest. Regions
around Chicago, St. Louis and Kansas City, Ohio and southern Michigan. There
are also sizeable operations in New England, in the Hudson Valley and upstate
Today, most of the mushrooms are grown in specially-constructed, win-
dowless houses where air circulation, temperature, moisture and humidity are
closely regulated to guarantee the most favorable growing conditions and
There are some successful commercial mushroom growers in the United
States who use caves and abandoned mines to raise their mushrooms. The
largest is Butler County Mushroom Farms, West Winfield, Pennsylvania.
Mushroom Spore The seed of the mushroom is called a spore. It is
of minute size and infinitesimal weight. You can get an idea of the size
when you know that one mushroom, permitted to mature and produce spores,
will create acropof sixteen billion seeds or spores. However, it is
estimated that only one out of a billion grows.
Mushrooms in New Products American grown mushrooms contribute their
unique flavor and texture to more and more of the new products that come to
the grocers' shelves. They appear in new spaghetti and barbecue sauces, in
de-hydrated soup packages, in may convenience packaged foods. They are
included in the new poultry and seafood dishes. Frozen mushrooms are gaining
popularity, especially where the fresh are unavailable at times.
How to Buy and How to Keep
How-to-Buy Mushrooms When mushrooms are first picked and packed,.the
veil is closed around the stem and the mushrooms are firm and dry-moist. Mush-
rooms are also perfectly good when opened, or when they have brown spots on
them. Size is merely a matter of preference. Small and very large mushrooms
may be exactly the same age and will have no special difference in taste or
Only after the mushrooms have stood unfrigerated too long will they be
dry and toughened. Or if left for too long and too closely covered in
the refrigerator they will take on a slick too-moist quality.
Mushrooms are Canned 62% of the annual production of mushrooms are
processed and 38% are sold fresh. Of this 62% processed, 45% are canned;
14% in mushroom soup; 3% frozen and other. Canned mushrooms can be bought
in virtually any food store every day of the year. They are available in
whole caps, sliced, and in stems and pieces. They come in various can
sizes to fit every purpose, and are convenient and easy to use. They are.
increasingly found on the kitchen shelves of the American homemaker; handy
for use to give their special touch to varied menus.
Keeping Qualities Freshly picked mushrooms will keep in prime
condition at about 32 degrees Fahrenheit, and with the relative humidity at
85 to 90 percent, for five days. At higher temperatures the storage period
should be shorter. In the house mushrooms should be kept in the refrigerator.
Oxidation causes a discoloration which, however, does not affect the flavor
or food value of mushrooms. They can, of course, be frozen and will keep for
much longer periods of time.
Don't peel mushrooms...in that velvety peel you'll find flavor, quality
Mushrooms should not be overcooked...ten minutes is plenty.
To wash mushrooms, rinse quickly in light stream of cold water. Never
let them soak in pan of water.
How-to-Marinate Mushrooms Try this for an emergency; Drain I eight
ounce can button mushrooms. Pour over them to cover, 1 bottle Italian or
French dressing (not the red kind). Let stand in refrigerator for at least
half hour--longer is better of course; or you can make your own vinegar and
oil French dressing. Drain and serve with picks for cocktails. Mighty good.
How to Saute Mushrooms Fresh or Canned Heat a large surface heavy
skillet or griddle. Add enough butter, or oil and butter together, to coat
surface generously. Keep adding as needed. When very hot but not dark
brown,.arrange mushrooms, slices, o whole mushrooms, all over the surface.
Test for heat. They-should begin to sizzle immediately.. Watch'carefully.
As sooh as, the edges begin to brown and the centers take on that clear
quality, turn each one.
Lightly brown on other side. Takes about 4 minutes. Lift out onto
soft paper toweling; Dust ever so lightly with salt and sometimes add a
pinch (small) of powdered ginger. Spear with picks and serve hot for cock-
tails. Whole caps should be browned first on the round side and turned
capside down to finish. Will require a bit longer than the slices.
Fresh Mushrooms Cooked--Snow White Clean and trim stem ends medium
size mushrooms. If small leave whole. Cut larger mushrooms into quarters.
In deepsauce pan pour I cup water and add 1 tablespoon lemon juice with 2
tablespoons butter.. Heat to bubbling boll. Add mushrooms and toss in
liquid coating each!mushroom. Cook quickly 5 minutes. Toss in pan two
or three times. Cool, stirring lightly several times. Refrigerate and use
as wanted for sauces, casseroles, to garnish or to serve as a vegetable.
Add scant salt when ready to serve. Do not salt mushrooms before cooking.
A bitof fresh dill added while mushrooms are hot adds a lilt.
EQUIVALENTS FOR FRESH AND CANNED MUSHROOMS
1 pound fresh mushrooms, or one can--6 or 8 ounces
pound fresh mushrooms, or one can--3 or 4 ounces
20 to 24 medium size mushrooms, or one can--6 or 8 ounces
10 to 12 medium size mushrooms, or one can--3 or 4 ounces
PRODUCTION OF.MUSHROOMS FROM SAWDUST
Technical Paper 158
S. S. Block, G. Tsao, and L. Han
This work was aimed at determining how effectively sawdust and other
cellulosicwastesmight serve as a medium for mushroom production. The
commercial mushroom, Agaricus.campestris, was cultivated on fortified, com-
posed gum wood sawdust. The yields on a weight basis were considerably
higher than commercial yields from horse manure compost. The wild, wood-
rotting mushroom, Pleurotus ostreatus, was grown in 2 weeks on sterile
sawdust medium fortified with oatmeal. On nonsterile, composted balsa wood
sawdust, the unusually high yield of 1.21 pounds of fresh mushrooms per
pound of dry sawdust was obtained. When fortified with soybean meal, the
yield was 1.41 pounds. In all experiments, the yields on a per square foot
basis were low, because of the low bulk density of the sawdust.
Fungi belonging to the basidiomycetes, many of which produce fruit
known as mushrooms, .are unique in nature i'n being able to degrade a wide
variety of natural,.polymeric substances. In the 18th century, in Europe,
this ability was utilized by the cultivation, on horse manure, of Agaricus
campestris, the common mushroom of commerce. In Japan, for several centuries
logs have been artificially Infected with a wood-rotting fungus, Cortinellus
shlitake, which produces a strongly flavored mushroom. In many countries,
different species of wild mushrooms are gathered and marketed.
The substitution of machines for draft horses has considerably reduced
this source of manure and racing stables are now the major suppliers. Syn-
thetic manures have been developed, but-as they utilize Ingredients which are
also employed in animal feeds, theygenerally cannot compete economically
with manure (9, 13, 14, 16, 19).
Woody tissue, the world's most abundant natural!1waste product, is
readily available in such forms as wood, sawdust, bark, bagasse, rice hulls,
and straw. In the United States the wood industries produced manufacturing
waste amounting to 53,000,000 tons, according to a 1944 report (20). The
part of these manufacturing wastes not used for fuel amounted to 20,000,000
Many basidiomycetes are able to diges-t wood directly to satisfy their
carbohydrate requirements (6); Some of these produce very tasty fruiting
bodies (mushrooms or sporophores). To identify wood-rotting fungi, Badcock
experimented with flask cultures of fortified sawdust and succeeded in
obtaining sporophores of 81 species (2,3). European reports (11, 12, 18)
demonstrated that A. campestris can be produced successfully on composted
sawdust. This paper enlarges on an earlier report (5).
Experiments with Agaricus Campestris
In the experiments with Agaricus campestris, the media were prepared
by composting, according to standard practice with manures. Not being a
wood-rotting fungus, A. campestris is unable to utilize wood directly, but
only if it has been subjected to prior partial digestion by composting.
Gum wood sawdust was used, because it was available locally and'was readily
composted. Cubical piles containing about 250 pounds each were prepared.
The amounts indicated in Table I are the quantities of the compost ingre-
dients contained in each of the trays used later for growing the mushrooms.
Three piles were assembled. The first was essentially sawdust forti-
fied with mineral salts and organic nitrogen in the form of soybean meal.
This pile did not heat up as rapidly as expected. Corncob meal was added
to the pile to stimulate fermentation and produce rapid:heating. This
procedure might not have been necessary had the pile been larger and had
it been given a longer time to compost. Because composted hay is a rich
source of nutrient for A. campestris, a second pile was prepared with half
hay and half sawdust. Nitrogen in the form of chicken manure, rather than
soybean meal, was employed in this pile, because protein nitrogen was supplied
by the hay. The third pile consisted of hay and corncob meal, a synthetic
compost sometimes employed for mushroom growing. Corncob meal was used
instead of cracked corncobs to reduce porosity and retain heat in the small
The piles were turned and reformed on the third, sixth, and ninth days
from the start of the experiment. On the twelfth day, the compost was put
into trays:and transferred to a small room heated to 1300 F. for continued
fermentation and some pasteurization. On the fourteenth day, the trays were
removed to the high-humidity growing room and 24 hours later were inoculated
with mushroom spawn. Each tray had an area of 2 square feet and was filled
with compost to a depth of 4 inches. The 22nd day after spawning, the trays
were covered (cased) with a 1-inch layer of soil. Mushrooms first appeared
about a month and a half after spawning and continued to appear in some cases
until the experiment was ended 3.5 months later (Figure 1). A temperature
of 680 F. and a relative humidity of approximately 85% were maintained in the
growing room throughout the experiment.
The yield data in Table 1 show that the sawdust produced about one
third less mushrooms per tray than the corncob-hay compost. The sawdust-
hay gave a very high yield in one tray, but a much lower yield in the
duplicate tray. On the basis of the weight of ingredients employed, however,
the yield of mushrooms was greater for the sawdust compost than for the corncob-
hay, because the latter weighed almost twice as much per tray. On a weight
basis the average yield from the sawdust-hay trays was considerably greater
than the other composts, inasmuch as it had the least bulk density. The'
yield was greatest the first month of bearing and then progressively decreased.
With the sawdust compost, about 85% of the mushrooms were produced in the
first 2 months of picking, whereas the corncob-hay compost yielded only about
65% of the total in the same period, but continued to bear well for several
Experiments with Pleurotus Ostreatus
Growth observations of the mycelia of the nine species of wild, wood-
rotting mushrooms on different sawdust media are given in Table II. Pleurotus
ostreatus, commonly known as the oyster mushroom, grew more vigorously on most
of the media and produced fruit more readily than the other species (Figure 2).
For these reasons, and because of its known edibility and growth at high
temperatures, Pleurotus ostreatus was selected for further experiments.
Table III gives the results of the production of P. ostreatus mushrooms
on pine and gum wood sawdusts. One gallon cans were partly filled with 120
grams of sawdust fortified with 6 grams of oatmeal and moistened with 250
grams of water. The sawdust medium was sterilized, in an autoclave, for 30
minutes at 15 pounds' pressure. Upon sterilization the cans were covered with
polyethylene sheets to prevent contamination and to retain moisture. When
the medium had cooled, it was inoculated with 21 grams of spawn per can. The
cans were kept in a room maintained at 780 F. and 85% relative humidity. In 10
days to 2 weeks, fruiting bodies began to appear and the first flush (crop) was
picked 15 to 17 days from the start of the experiment. After 47 days, the
experiment was terminated. The yield from gum wood sawdust was twice that
Table 1. Production of A. campestris Mushrooms from Composted Gum Wood Sawdust
Gum wood sawdust 1410 605 ---
Corncob meal 282 --- 1505
Soybean meal 141 --- ""
Hay (timothy) --- 605 1505
Chicken manure 14 181 450
Urea 21 18.3 45.4
Calcium sulfate dihydrate 35.4 30.6 76
Potassium chloride 17.8 14.6 36
Calcium superphosphate 7 5.8 15
Time, days 14 14 14
Temperature, o F. 140-170 140-170 152-162
Time, spawning to casing, days 22 22 22 22 22 22 22
Time, spawning to fruiting, days 44 44 46 44 46 43 44
Duration of fruiting, days 116 121 144 98 150 148 150
No. of pickings Ist month 12 11 14 12 19 11 15
Wt. of crop Ist month, grams 806 802 778 520 1401 861 1029
No. of pickings 2nd month 8 7 13 5 9 9 9
Wt. of crop 2nd month, grams 452 336 278 147 567 382 487
No. of pickings 3rd month 4 3 5 4 4 6 6
Wt. of crop 3rd month, grams 128 67 116 87 119 217 234
No. of pickings 4th month 4 5 5 1 8 6 10
Wt. of crop 4th month, grams 56 60 144 32 320 281 203
No. of pickings 5th month 0 0 4 0 6 7 6
Wt. of crop 5th month, grams 0 0 46 0 90 168 182
Total yield, grams 1442 1265 1362 786 2497 1909 213F
Wt. fresh mushroom/wt. dry
ingredients 0.75 0.66 0.71 0.54 1.71 0.53 0.59
Pounds fresh mushrooms/sq. ft. 1.59 1.39 1.50 0.87 2.75 2.11 2.31
Table II. Growth of Mycelium of Wood-Rotting Mushroom Fungi on Sawdust Media
Medium Cv P
aFp it nn ne ,,rp
Growth of Fungi (Sca
Ct Pf Am Hc
1 1 1 1
1 1 1 1
1 1 1 I
1 1 1 1
2 2 + 2
+- 2 + 1
+ 2 + *1
KEY TO TABLE II
Abbreviations Organisms Abbreviations Media
Cv Collybla velutipes A 20 grams pine sawdust +
Po Pleurotus ostreatus 40-ml. water
LI Lentinus lepideus B 20 grams pine sawdust +
Ab Agaricus blaze 40 ml. Czapek solution
Ps Polyporus sulphurous C 20 grams pine sawdust + 1
Ct Clitocybe tabescens gram acceleratora + 42
Pf Polyporus frondosus ml. water
Am Armillaria'mellea D 16 grams pine sawdust +
Hc Hydnum coralloides 8 grams oatmeal + 8
grams CSMAa + 64 ml.
aCzapek soln., dilute solution of min- water
eral salts (17). E 16 grams pine sawdust +
Accelerator, nutrient mixture of corn 8 grams oat grains +
meal, bone meal, and similar materials (2). 8 grams CSMA" + 64 ml.
CSMA, medium containing bran and grains water
used in rearing flies, according to Chemi- F 16 grams bagasse + 32 ml.
cal Specialties Manufacturer's Assoc. water
G 20 grams pine sawdust +
6 grams oatmeal + 52
H 20 grams oak sawdust +
40 ml. water
I 20 grams gum sawdust +
40 ml. water
J 20 grams oak sawdust +
4 grams oatmeal + 48
K 20 grams gum sawdust +
4 grams oatmeal + 48
Growth of Pleurotus ostreatus Mushrooms on Rice Hulls
First Flush Second Flish
Time, Weight, Time, Weight, Yield,
Replicate days -"grams days grams Grams
1 14 22.0 31 13.0 35.0
2 14 ,19.0 -- 19.0
3 15 24 .0 -- -- 24.0
Wt. fresh mushrooms/wt. dry ingredients 0.20
Rice Hulls + 5% Oatmeal
1 14 30.0 31 14.0 44.0
2 19 29.5 35 31.5 61.0
3 19 26..0 35 20.0 46.0
Wt. fresh mushrooms/wt. dry ingredients 0.38
Rice Hulls + Gum Wood + 5% Oatmeal
1 14 35.01 35 11.0 46.0
2 14 33.5 36 19.5 53.0
3 14 23.5. 29 16.0 39.5
Wt. fresh mushrooms/wt. dry ingredients 0.35
Table V. Yield of Pleurotus ostreatus Mushrooms Grown on
'. '; .Gum Wood Sawdust
First Flush Second Flush Third Flush
Time, Weight,. Time, Weight, Time, Weight, Yield,
epi icate days grams days grams days grams Grams
18 19 37 37 -- 54
2 18 37.5 37 7 50 23.5 68
3 18 36.5 37 10.5 55 18.5 65.5
4 18 34 38 14 55 21 -69
5 19 26.5 45 23 63 15 64.5
6 19 33 40 34 63 9.5 76.5
7 21 31.5 46 19 -- -- 50.5
Total 218 144.5 87.5 448
Wt. fresh mushrooms/wt. dry ingredients 0.48
There was insufficient compost to make replicate trays. However, the
plain balsa, and especially the balsa with soybean meal, produced very high-
weight yields. The yield of mushrooms per unit area was low because of the
.-small weight of balsaqcompost per square-foot, 4 inches deep. However, the
high efficiency of its conversion to mushroom tissue is demonstrated in the
case of the balsa with soybean, where the residue was weighed and the weight
The data demonstrate that good yields of mushrooms can be produced
from sawdust as compared with the yields obtained in the commercial production
of Agaricus campestris from horse manure compost. Three pounds of mushrooms
per square foot of bed space in a commercial plant is considered a very high
yield. in reported experiments (15), Sinden and Hauser give yields of 400
pounds of mushrooms from a ton of manure containing 50% moisture. This is
equivalent to 0.4 pounds of mushrooms per pound of dry manure. Probably the
highest yields found in the literature are those of Lambert and Ayers (10)
whose best trays in controlled, small-scale experiments gave better than
.6 pounds ofmushrooms per square foot or, on a weight basis, 0.9 pound per
pound of dry manure. Table I shows that sawdust fortified with corncob and
soybean meal gave an average.of 0.71 pound of A. campestris per pound of
sawdust compost and an average of 1.13 pounds of mushrooms per pound of
With P. ostreatus, balsa wood fortified only with inorganic salts gave
a yield equivalent to 1.21 pounds of mushrooms per pound of sawdust, whereas
balsa fortified with soybean meal and mineral salts gave 1.41 pounds per
pound. Recognizing that these are merely small scale, exploratory experiments
requiring confirmation, they nevertheless show the favorable possibilities for
the use of sawdust in mushroom production.
In experiments with sawdust, Rempe (12) found hardwood, such as beech,
Preferable to. conifers, such as pine and spruce. Results of isolated experi-
ments in this laboratory with oak and magnolia sawdusts show that -mushroom
production is not limited to the wood species already mentioned.
The yields from sterile sawdust were comparable with those obtained
In commercial practice. Thehighest yield (76.5 grams equivalent to 0.58
pound of mushrooms per pound of sawdust, Table V), however, was considerably
lower than those obtained with composted sawdust (Tables I and VI). A
possible explanation for the superior results with the composted sawdust is
the-partial degradation of wood fibers which occurs during composting and
makes the.sawdust more easily digested by the mushroom. While composting
Permits higher yields and makes the sawdust resistant to competitive micro-
organisms, compositing conditions are reproduced so rarely that two composts
are practically never alike. The changes which occur during composting are
extremely complex and therefore difficult to control. The small laboratory
i composting can, developed and employed in these experiments, may help to pro-
vide more uniform composts which will give reproducible results.
Table VI. Production of Pleurotus ostreatus Mushrooms from
Balsa Wood Sawdust
1 2 3 4
Balsa wood sawdust
Rice hulls inoculum
Temperature, o F.
Time, spawning to casing, days
Time, spawning to first flush, days
Wt. of first flush, grams
Time, first to second flush, days
Wt. of second flush, grams
Time, second to third flush, days
Wt. of third flush, grams
Time, third to fourth flush, days
Wt. of fourth flush, grams
Total yield, grams
Wt. of fresh mushrooms/wt. dry
Pounds fresh mushrooms/sq. ft.
Dry wt. of compost residue, grams
Wt. lost, grams
Efficiency, a %
aDry .wt. of product'based on dry wt.
Although the yields from sawdust on a weight basis appear most encour-
aging, a practical grower is more impressed with the amount of mushrooms ob-
tained from a bed or a house. Because of the light weight of sawdust, as com-
pared with that of manure, and of the shallow trays employed, the yields on an
area basis were low. Rempe s work indicates, however, that deeper beds will
permit higher per area yields. He obtained 2.5 pounds per square foot with
8-inch-deep beds (12). As noted in Table VI, production of mushrooms from
the sawdust was fairly rapid, thus making possible frequent turnover and
multiple utilization of bed space during the year.
From an economic standpoint, sawdust has certain advantages over manure.
It is available in more localities and easier to handle, mix, and turn. It
has been estimated (12) that it will permit a saving of at least 50% on trans-
portation and labor costs for compost materials. If It costs 22 cents to
produce a pound of mushrooms, about 10 cents of this is made up of transporta-
tion and labor costs, 5 cents is overhead, and 7 cents represents the cost of
manure. Thus, sawdust offers a potential saving of 23% over manure, If material'
costs, overhead, and yields are the same. Where the sawdust would be avail-
able at no cost, the saving would be 55%
As shown in the photographs, P. ostreatus is very different from A.
campestris. Pleurotus does not grow in the familiar button form characteristic
of young Agaricus. It does not have the thick "meaty" tissue of the Aqaricus
buttons. In shape and growth it resembles more closely the Japanese shlitake
mushroom. Like the latter, it has a tough, inedible stem. The flavor, however
is more like that of A. campestris. Pleurotus would appear to have its
greatest value as a flavoring ingredient for soups, sauces, and gravies rather
'than as'a'fresh mushroom for table use.
Mushrooms are a source of essential amino acids and of the B vitamins
(1, 4, 7, 8). They can be "factory-produced" the year around from waste pro-
ducts which originate from nondepleting sources and may be visualized as an
important food so':rce for the future. Full realization of the market poten-
tial, however, awaits more efficient production and lower cost.
1. Anderson, E. E., Fellers,-C. R., Proc. Amer. Soc. Hort. Sci. 41, 301-304
2. Badcock, E. C., Brit. Mycol. Soc. Trans. 25, 200-205. (1941).
3. Ibid., 26, 127-132 (1943).
4. Block, S. S., Stearns, T. W., Stephens, R. L., McCandless, R. F. J., JI
Aqr. Food Chem. 1, 890-893 (1953).
5. Block, S. S., Tsao, G., 129th Meeting, ACS, Dallas, Texas, April 1956.
6. Davidson, R. A., Campbell, W. A., Blaisdell, D. J, J. Anr. Research 57,
7. Esselen, W. B., Jr. Fellers, C. B., Mass. Agr. Exp.:Sta. Bull. 434, 1-11
8. Humfeld, H., Sugihara, T. G., Food Technol. 3, 355-356 (1999).
' 9. Lambert, E. B., Farmer's Bull. 1875, 12 (1941).
10. Lambert, E. B., Ayers, T. T., Plant Disease Reptr. 36, 261-268 (1952).
11. Niethammer, A., Zentr. Bakteriolog. 2, 129-130 (1942).
12. Rempe, H., Mushroom Sci. 2, 131 (1953).
13. Sinden, J. W., Pa. Agr. Expt. Sta. Bull. 365, 1-27 (1938).
14. Ibid, 482, 1-26 (1946).
15. Sinden, J. W. Hauser, E., Mushroom Sci.1, 52-59 (1950).
16. Stoller, B. B., Plant Physiol. 18, 397-414 (1943).
17. Thom, C., Church, M. B., "The Aspergilli," p. 39, Williams & Wilkins,
18. Treschow, C., Danske Botan..Arkiv. 11, 1-180 (1944).
19. Waksman, S. A., Reneger, C. A., Mycologia 26, 38-45 (1934).
20. Winter, R. K., Chidester, G. H., Hall, J. A., U. S. Dept. Agr. Forest
Serv. Rept. 4, Wood Waste in U. S. (1947).
SOME COMMON EDIBLE AND POISONOUS MUSHROOMS
Cornell Extension Bulletin 386
H. M. Fitzpatrick and W. W. Ray
The terms mushroom and toadstool are used by many collectors to
designate respectively edible.and poisonous species. Such a distinction is
not recognized by the scientist. The two words are correctly used inter-
changeably, though mushroom is usually preferred. Mushrooms, as commonly
thought of, have a characteristic umbrella shape. The handle is termed the
stem, the expanded top the cap.. The stem may be attached at the center of
the cap or at one side or it may be absent. On the undersurface of the cap and
radiating from the stem, as the spokes of a wheel from the hub, are numerous,
prominent, flat, knife-blade like plates called gills. On the surface of the
gills are produced a countless number of minute spores, which are analogous to
seeds of green plants. Though these spores are much too small to be seen by
the unaided eye, they fall from the gills in such large numbers that they
accumulate as a visible powder. The color of this spore powder is always the
same in any given species of mushroom. To determine whether a form is edible
or poisonous, one must know the color. In the well-known cultivated mushroom
this spore powder is purplish brown, while in the deadly poisonous species of
Amanita it is white.
If the cap of a freshly collected mature mushroom be placed gill-side
down on a sheet of paper, the falling spores soon accumulate on the paper
between the edges of the gills in radiating lines forming an attractive
spore print in which the color is unmistakable. While the spores are falling,
the cap should be covered with an inverted dish to provide still air conditions.
In nature, the extremely light spores drift away easily in air currents and
are widely disseminated. The spores fall to the ground and germinate at the
surface of the soil, forming in the humus a tangled mass of slender threads
which the mushroom grower calls spawn. These threads are the vegetative, or
feeding, portion of the mushroom. The prominent umbrella-shaped body above-
ground is merely the fruit body. It forms at the tip of one of the coarse
threads composing the spawn, and in the young condition is known to the grower
as.a button. The button commonly originates somewhat beneath the surface of
the ground, and in the beginning is very small and more or less spherical.
With increase in size the various parts of the mature mushroom begin to take
form in its interior. At maturity the stem elongates rapidly elevating the
cap well aboveground. Finally, the cap,opens out into the horizontal position
giving the open umbrella shape.
Most.mushrooms grow on the ground, but a goodly number also occur on
wood. Mushrooms belong to the large group of plants known as the fungi.
Other fungi besides mushrooms are edible. There are polypores, (figure 7),
which have pores on the underside of the cap in place of gills; the coral
fungi (figure 8), which are usually branched in a tree-like fashion and
resemble coral; the morels (figure 10) whose cap is pitted on the upper
surface and looks like a sponge; and the puff-balls, (figure 9), round
bodies which when young have a homogeneous white appearance inside and
S when old are completely filled with a brown mass of spore dust.
The only way to be sure whether a mushroom is poisonous or edible
is to be able to recognize it on sight as one would a violet, a rose, or a
lily. There is no dependable test, such as the "silver spoon test" or the
"peeling of the cap," that will enable an inexperienced person to distinguish
poisonous from edible forms.
Some general rules for mushroom collectors are the following: Never
eat a mushroom until you are sure of Its identity. Be sure all mushrooms
collected are fresh. In general, do not use brightly colored forms, for some
of these are somewhat poisonous. Reject all forms that have a cup around
the base of the stem. View with suspicion all forms with white gills or
white spore dust. Use great care not to pick any mushroom in the early
button stage, since in that condition all distinguishing characters are
not yet well developed..
The purpose of this bulletin is to describe a few of the common edible
forms, which, at the same time, are among the easiest to identify. If one
can master these and cares to learn more, many books, scientific and popular,
describe and illustrate numerous other forms. One of the most outstanding
of these is Studies of American Fungi. Mushrooms: Edible, Poisonous. Etc.,
by George Francis Atkinson. Most of the illustrations in this bulletin are
copied from those in that book. More recently published and more readily
obtainable books include: Mushrooms and Toadstools, by H. T. Gussow and
W. S. Odell; The Mushroom Handbook, by Louis C. C. Krieger; Common Edible
Mushrooms by Clyde M. Christensen; and Field Book of Common Gilled Mushrooms,
by William Sturgis Thomas.
The Common Field Mushroom
Anyone familiar with the commercial mushroom Should be able to identify
this wild form (Agaricus campestris), for it is nearly identical with the com-
mercial form in shape, size, and color (figure 1). The common field mushroom
is found in pastures and grassy places, especially if the ground has been
richly manured. It usually grows In groups, but occasionally is single. From
August until frost it is common when rainfall isplentiful.
The cap is from 1 to 4 inches wide; hemispherical at first, and expanded
at maturity. :The surface in young plants is nearly smooth, presenting a soft,
silky appearance. As the plant becomes older, the surface may be torn into
small triangular scales. Usually the color i:s white, but varies to light
brown, especially in the scaly forms, where the scales may be prominent and
dark brown in color. The flesh is white.
In the young plant, a thin membrane, called the inner veil stretches
from the edge of the cap to the stem and hides the gills from sig t. As the
umbrella opens the expansion of the cap ruptures the veil which then hangs
in a ring, the annOlus, around the stem.
The gills in the button stage are white. They soon turn pink and,
when the cap expands and breaks the veil, they become dark-brown to purplish
black. They are free from the sVem.
The stem, from 2 ib 3 inches long and from 1/2 to 2/3 inch thick, is
cylindrical, white, and solid throughout.
Poi 6nous Mushrooms Amanita
A number of different species of mushrooms belonging to the genus
Amanita are deadly poisonous, and deaths caused by eating them are not infre-
quent. Eating even a small amount is dangerous. The symptoms of poisoning
develop slowly, and in consequence, the physician is often called too late.
It is imperative, therefore, that the collector be able to recognize Amanita.
In all species of Amanita the spores are white. Even in old specimens
the gills are usually white. The stem bears a prominent annulus. In the
young, or button, stage the fruit body differs from that of most other mush-
rooms in that it is enclosed In a definite membrane. This is called the volva.
The maturing button enlarges rapidly and bursts the volva; the mushroom emerges
from it and pushes upward until well aboveground. The entire membrane is
commonly left behind surrounding the base of the stem as a cup. This has
been called the death-cup, and its presence carries the warning that the
mushroom in hand is probably a poisonous species. Sometimes, however, the
volva fails to persist as a definite cup at the base of the stem. Instead,
it may break into fragments some:which are carried upward on the surface
of the cap where they may be seeh.at maturity as loosely attached scales.
When collecting mushrooms, it is a good rule for one to dig to the very base
of the stem to determine whether the'cup is present or absent. If a cup is
not found, then a search iShould be made for fragments of the volva at the
base of the stem and on the surface of the cap.
As a volva is present in all species of Amanita and is lacking in most
other mushrooms, any indication of its presence should constitute a warning,
even though a well-formed cup be absent.
The Fly Agaric
The Fly Agaric, a poisonous form, often grows along roadsides near
trees, or in groves, and at the edges. of woods.
The cap in the young stages of development is rounded, but at maturity
is flat on top (figure 11). It measures from 4 to 6 inches broad. The color
varies from a yellow to orange-red, but in old forms it is nearly white.
White to yellowish scales which are fragments of the volva often are present
on the surface of the cap, but they may be totally absent. The gills and
stem are white, and the bulb-like structure at the base usually is marked
by prominent concentric scales forming interrupted rings. The stem is
.'from 4 to 8 inches longand from to I inch thick.
The Destroying Angel (figure 12) is one of the most poisonous of the
mushrooms, and its white color makes it especially dangerous in that it is
easily confused with Lepiota naucina or Agaricus campestris. As it has a
prominent death cup, the careful collector will recognize it. Failure to
dig to the base of the stem in search of the cup, has, however, frequently
resulted in disaster. Since the entire volva commonly is used to form the
cup, warning scales ordinarily are not present on the surface of the cap as
in the Fly Agaric. The cap of the Destroying Angel is bell-shaped when
young to fully expanded and flat when mature. It is from 3 to 5 inches broad
and pure white in color. It is slimy in wet weather.
A related species, the Deadly Agaric (Amanita phalloides), is sometimes
white, but more often is yellowish, greenish, or olive brown. In it the
death-cup is often less well formed than in the Destroying Angel and there
are prominent scales on the cap. Still other poisonous species of Amanita
differ in color, size, and shape. The death-cup Is much more evident in
some species than in others.
PHYSICAL SPECIFICATIONS OF MUSHROOM PROCESSING PLANTS
Progress Report 309
C. W. Coale, Jr., W. T. Butz, and G. D. Kuhn
Mushroom production is the single most important cash crop in Pennsyl-
vania. The value of the mushroom crop during the 1968-69 crop year amounted
to $42.5 million. In comparison, the combined value of all fruit grown in
Pennsylvania during 1968 totaled only $31.5 million, according to the Penn-
sylvania Crop Reporting Service.
Mushroom production in the United States amounted to nearly 190 million
fresh pounds during the 1968-69.crop year. Output by Pennsylvania producers
totaled 121 million pounds, or:64 percent of the United States' production.
Mushrooms are marketed, in fresh or processed form. In recent years,
about three-fourths of the mushrooms grown in the Commonwealth have been
processed. Canning, as contrasted to freezing or drying, represents the
principal type of processing.
Statement of the Problem
Prior to the early sixties, the industry allocated only limited
resources to research and development of new techniques, new products, and
new markets. For example, mechanization of mushroom processing techniques
has proceeded more slowly than in most other food processing industries.
The industry has remained highly labor intensive, and as a result has faced
severe price competition from mushrooms processed in.countries in which
wage rates are considerably lower than in the United States.
One of the basic needs of the industry, therefore, is to develop more
efficient methods of processing. In particular, if the industry is to
remain competitive with foreign processors, the domestic industry must
develop processing techniques that conserve labor. For this reason, the
economic-engineering approach used in the present study focused on labor-
saving methods. The results are summarized.
CASING SOIL TREATMENT IN COMMERCIAL MUSHROOM PRODUCTION
Special Circular 139
L. C. Schisler and P. J. Wuest
After the compost is "seeded" with grain spawn, the growing room is
kept at a temperature of around 750 F. with high humidity (over 90 percent)
for two to three weeks, This period is called "spawn run." After full
spawn run, an inch of pasteurized soil is applied to the surface of the
compost; this soil is called the casing layer.
Soil used for casing mushroom beds should be pasteurized to remove
pests which may be harmful to the mushroom crop. Some growers do not pasteurize
soil taken from areas in which mushroom farms are not located. This is a
dangerous practice since most soils contain pests which may cause considerable
damage to the crop. Needless to say, soil collected from mushroom-growing
areas will probably contain great numbers of the common mushroom pests,
therefore making pasteurization essential.
Several methods of pasteurizing casing soil are available to the mush-
room grower. Soil pasteurization can be divided into two main categories:
heat treatment and chemical fumigation.
WATERING AND VENTILATING FROM CASING THROUGH CROPPING IN
COMMERCIAL MUSHROOM PRODUCTION
Special Circular 140
S L. C. Schisler and P. J. Wuest
Casing has been practiced since the 17th century to induce development
of sporophores. That mushroom mycelium will not produce fruiting bodies in
any quantity until cased with a suitable material is well known. The exact
function of the casing in initiating fruiting has never been proven experi-
The importance of obtaining a good suitable casing material cannot be
overemphasized. The proportion of the yield potential of any compost which
will ultimately be realized is largely dependent upon the type of casing
material and subsequent management of it.
Vartous'materials are Used for casing throughout the world and seem
to give satisfactory results. In the United States, and in Pennsylvania in
particular, a loam topsoil with good structure is recommended if available
to the grower. Management practices vary depending on the type of casing
layer used by the grower. This discussion will be confined primarily to
practices involved in management of loam topsoil with good structure.
Soil structure is the arrangement or grouping of soil particles into
aggregates or granules. A soil granule is a rounded porous mass of mineral
particles of varying sizes held together by humus, clay, and water attractions.
The most important ,ffator is humus or organic matter. Mineral soils in some
parts of the United States may contain up to 12 percentorganic matter, but"
Pennsylvania soils usually have between 1 and 5 percent. Yet this small
amount of organic matter makes the difference between good and poor structure.
Plant roots, soil fungi, and bacteria are the main contributors to this
effect of holding the soil particles together. Casing soils from grass or
legume sods aretisually much more desirable than soils under intensive cul-
tivation. These soils can be improved by establishing a sod on them fod
two or more years prior to use for casing.
Sometimes good structure when it exists in soils in the field is
destroyed by mismanagement. Field soils to be used for casing should never
be tilled or worked in any way when excessively wet. Water acts as a lubri-
cant for the clay particles which are plate-like rather than round so that
they move over each other like shingles on a roof. This puddled structure
is impervious to air and water.- Excessive discing of soil to be used for
casing should be avoided as this operation mechanically destroys soil aggre-
gates. Tillage should be reduced to the minimum necessary to reduce clods '
for convenient screening. Dry soil can also be damaged by tillage, reducing'
The optimum condition for working soil is when it is friable, or
crumbly. When the soil is slightly compressed in the hand, the granules
tend to hang together. It feels soft to the touch. The moisture content
should be at the level considered optimum for casing or tillage. The soil
is too moist when it'!is of! a plastic consistency and can be molded.- : .''';
Now, why is it desirable for casing soil to have good structure? A
well-aggregated soil is desirable so that during the management of the
mushroom crop the soil is maintained in optimum physical condition for the
proper gaseous exchange from compost to air and vice versa, and also to
allow for proper water-holding capacity of the casing layer. In an average
loam soil with good structure, pore space makes up approximately 50 percent
of the total volume of a soil. If the structure is destroyed by mismanage-
ment, much of the pore space is lost. It is this pore space which is
involved in proper gaseous exchange and water-holding capacity. These two
factors reflect themselves in increased yield and size of mushrooms.
Proper gaseous exchange involves the need of the mycelium for a suf-
ficient supply of oxygen to carry on normal metabolic processes. Also other
substance produced by the mycelium must be allowed to diffuse away from the
mycelium (C02 and other metabolic products). If a soil does not have suffi-
cient aggregation, It will break down under watering, slake over, and seal.
If sealing over occurs before the mycelium is through the casing soil, no
mushrooms will form in the.area. If the soil puddles after the mycelium
is up through the soil, mushrooms form but ultimate yield and size are
Mushrooms are normally 90 percent water. Most of this water is
derived from the water reservoir in the casing layer. Any reduction in
soil aggregation reduces the supply of available water.
Soil to be used as the casing layer must be pasteurized prior to use.
This is done to kill most of the pathogens which are harmful to mushrooms,
either by heat treatment (usually with steam) or by chemical fumigants.
Watering and Ventilating
After full spawn run (figure 1) the beds are cased to a depth of
approximately l" inches. The soil is friable with good structure (figure 2).
The first of the initial waterings begins immediately after the casing
operation has been completed.
We speak of mushroom growing today as a science. Watering is one
phase which remains, partially at least, In the art category. Methods of
watering differ throughout the mushroom industry. Some growers do not
water until the mycellum fuzzes up to the surface of the casing soil.
Some delay watering until the pinheads begin to form. Some maintain a moist
soil at all times, adding water as needed. Whichever method is used, the
main emphasis is to water so as to minimize destruction of soil structure
thereby preventing the sealing over of the beds, and still get enough
moisture into the soil for proper production.
Before beginning to water, adjust the water pressure so that a fine
spray will fall in a gentle arc onto the surface of the soil approximately
1 feet from the rose face (figure 3). It is Important when watering the
beds to maintain the same position of the rose face relative to the soil
surface whether the top, middle, or bottom bed is being watered. This
insures that the fine spray from the rose face will fall in a gentle arc
,;~ --35- .
on all beds, thereby minimizing destruction of aggregation at the soil
surface (figures 4, 5, and 6). Growers are often concerned about unpro-
ductive areas in their beds. Investigation occasionally reveals no
pathogens present but only the soil sealed over, apparently caused by
directing a forceful spray right atthat spot on the surface, or a leaky
rose face connection where more water actually ran out of the connection
onto the beds than passed through the rose face.
The number of Initial waterings required to bring the soil moisture
to the desired level will vary, depending on the amount of water per appli-_
cation (governed by rapidity of watering, size and number of holes in rose
face, and water pressure) and water-holding capacity of the soil. The
object of the initial waterings is to bring soil moisture to the desired
level without destroying soil structure. This can generally be accomplished
during the first four days after casing with four to eight waterings. The
soil should be "glistening" but should also be checked to be sure moisture
is present throughout the entire depth of the casing layer (figure 7). Soil
should stick to the finger if the proper level is reached.
Ventilation should be kept to a minimum during this period of initial'
watering, until the mushroom mycelium wefts up to the surface of the soil
in spots (figure 8). The humidity should be maintained as high as possible
(over 90 percent) by frequent watering of walls and floors. Before the
mycelium "lays over" and begins to grow over the surface of the soil, vents
should be opened to reduce CO2 concentration in the air on the bed surface
to less than 0.1 percent (figure 9). This level of CO2 should be maintained
Within a few days surface mycelial strands begin to thicken (figure
10) and tiny "clumps" of mycelium form (figure 11). This is the critical
stage of pin initiation and the pattern of fruting can be determined by
the time of water application. If the first of the series of first break
waterings is applied during the clumping stage, fewer first break pins will
develop, total"ffrst break yield will be reduced, and the size of individual
mushrooms is generally increased. When the watering is applied between
"clumping" and first pin formation (figure 12), more pinning develops and
first break yield is enhanced. If pinning is allowed to develop fully
(figure 13) before water is applied, maximum first break pinning occurs and
the largest first break yield will be obtained, but the size of the individual
mushrooms may be decreased. If care was not exercised during initial waterings
and the casing soil was puddled, cracks will form in the soil and mushroom
mycellum will emerge only through the cracks (figure 14). Clumps begin to
form (figure 15) and pins develop (figure 16) as on non-sealed-in soil, but
yield is reduced. Regardless of when the first break waterings are begun,
an attempt should be made to build up the moisture content of the soil to
its maximum water-holding capacity. More water per application is possible'
during the first break waterings than during initial waterings (figure 17). '~
As was mentioned earlier, soil fungi have an aggregating effect upon the
soil. Mushroom mycelium also exhibits this same effect. Therefore, after
the mycelium is in the soil, the soil is more resistant to breakdown and
increased water can be applied. First break waterings should not be applied
on successive days. Several waterings may be applied in one day If the soil
is receptive to water, but a day should elapse before the next waterings are
applied. Waterings should cease when mushrooms reach prebutton stage, that
is after enlarging but before full cap differentiation (figure 18). Further
watering is of no benefit to the first break mushrooms and only increases
the possibility of bacterial blotch.
If proper watering procedures were followed, a uniform heavy flush
of good quality mushrooms should result (figure 19). As the first break
is going off and before the last of the first break mushrooms are picked
(figure 20), beds should be trashed if necessary, and the first of the
second break waterings should be applied. More than one watering may be
applied the same day, but aday should elapse before the next waterings
are applied. Second break pins enlarge rapidly (figure 21). Waterings
should cease when mushrooms reach the prebutton stage (figure 22). The
soil should be at its maximum water-holding capacity at this time. If
proper procedures were followed, a uniform heavy flush of good quality
mushrooms should result (figure 23).
Similar procedures should be followed between later breaks, keeping
in mind that generally more time to water will be available between breaks,
and less water will need to be applied as the yield of successive breaks
decreases. Third breaks, however, can still be heavy (figure 24) and may
sometimes require considerable water, particularly when following a heavy
HARVESTING THE COMMERCIAL MUSHROOM CROP
Special Circular 141
L. C. Schisler and P. J. Wuest
Knowing exactly when mushrooms are ready to be picked requires training
and considerable experience. There is no single criterion on which to base
one's decision as to whether or not a mushroom is ready for harvesting. Size
is not a good indicator, for mushrooms of varying sizes may be at the same
stage of maturity and ready for harvesting.(figure 1). Some important
characteristics to consider are length of.stem in relation to diameter of
cap, and shape of cap in relation to exposure or stretching of the veil.
These characteristics can perhaps be best illustrated in the following
photographs. In the young mushroom (figure 2), even of considerable size,
the round thick cap is of nearly the same diameter as the base of the short
stem. As the mushroom enlarges (figure 3),, the round cap begins to increase
to a greater diameter than that of the stem. Upon further development
(figure 4) the cap continues to expand and the stem begins to lengthen.
The cap flattens, assuming a less rounded shape and the stem continues to
lengthen. As the mushroom reaches a proper maturity for harvesting (figure 5)
the veil becomes exposed. The edge of the cap has not unrolled and the veil
is not stretched. The stem has lengthened and a "tight" first quality
mushroom is ready for harvest.
The exact stage at which to pick mushrooms depends on the intended
market of the individual grower. Post-harvest handling of the product
also influences when mushrooms should be picked; however, most mushrooms
should be harvested at the stage illustrated in figure 5. Mushroom pickers
must learn to recognize when mushrooms are ready for harvest as viewed from
"-.- the picking position, since they will rarely have the opportunity to view
;A i the underside of the mushroom. Mushrooms in this section (figure 6) are too
young;the picker should move to the next section of the bed. Here (figure 7)
the mushrooms are larger than the previous ones, but most have not matured
sufficiently for harvest. Finally, the picker arrives at a section (figure 8)
where the stems have lengthened and the caps are sufficiently expanded to
justify harvesting some of the mushrooms. Continued stem lengthening, cap
expansion and appearance of veil (figures 9 and 10) results in the majority of
these mushrooms being ready for harvest. Failure to harvest at the proper stage
allows for continued unrolling and flattening of the cap, as well as
breaking of the veil (figure 11). Such mushrooms are poor quality (figure 12)
and have little economic value. i
ir Allowing mushrooms to become overmature before harvesting not only
decreases quality but reduces picking efficiency, and this is especially
true in the case of large first break clusters (figure 13). Individual
mushrooms are difficult to pick from a tightly grown cluster of mushrooms
with expanded caps. Mushrooms which appear singly or in small clusters on
later breaks are sometimes difficult to judge due to their large size and
"holding quality," that is, they seem to mature more slowly. However, the
same characteristics mentioned earlier can be used to determine when the
mushroom is ready for harvest.
In figure 14 the stems of the mushrooms are still somewhat shortened
and although caps have begun to expand, the edge of the cap remains tightly
rolled under. In figure 15 the mushrooms are now ready for harvest, as the
stems have lengthened and the cap edge has begun to unroll exposing the veil.
Failure to harvest at this stage allows the veils to stretch (figure 16) and
break within a few hours (figure 17). New pickers should pick from the same
sections on successive days. This will help them to determine whether they
are harvesting the mushrooms at the proper time.
Cutting Mushrooms For Fresh Market or Cannery Processing
Mushrooms should be picked with a twisting motion (figure 18). A
minimum amount of rhizomorphs and casing are removed, and adjacent pinheads
are less likely to be injured when a twisting motion is used for picking.
Several mushrooms should be Individually picked (figures 19 and 20) and held
in the hand before trimming (figure 21). Mushrooms are trimmed by making
a cut at the base of the stem to remove the rhizomorphs and clinging soil.
The cut should be made at the proper place and angle (figure 22). The
second and fourth mushrooms from the left are "square" cut at the proper
stem location. Others show a variety of the common errors in cutting.
Trimming mushrooms with a sharp knife Insures clean-cut stems (figure 23)
rather than ragged, rough stems (figure 24). Knives used for trimming should
be regularly sharpened, for ragged and rough stems reduce the keeping quality
and adversely affect the appearance of the harvested product.
When picking mushrooms from clusters such as appear on first break
(figure 25), begin at the edge of the cluster (figure 26) and remove mature
mushrooms singly (figure 27), being careful not to disturb or remove immature
pinheads at the base of the cluster. These may mature later in this flush
or form the basis for the next flush. Never pull out an entire cluster since
the casing will probably be dislodged with the mushrooms (figure 28). The
pins located in the dislodged casing can never mature, so such a practice
reduces yield. Proper trimming is almost impossible when mushrooms must be
cut from the clump (figures 29 and 30).
Some Do's and Don'ts of Mushroom Picking
1. Failure to twist out mushrooms results in lost yield and "capless"
stems on the bed (figure 31). If this does occur, the stems should be removed
immediately and cut while they are still usable for cannery processing. The
following day they become waste.
2. Fill baskets to the proper level (figure 32), don't overfill
(figure 33). Mushrooms are easily damaged in an overfilled basket or they
may simply "spill over."
3. Never leave pieces of mushrooms (figure 34), trash, or stumps
(figure 35) on the beds after harvesting. Spores can be shed from pieces
of cap tissue which, if virus infected, can cause the spread of this disease
throughout the house. The pieces of stem tissue and stumps can decompose
(figure 36) into a foul smelling, wet mass which can serve as a center for
spread of various mushroom pathogens.
4. Place cut'mushrooms in the picking basket and the "stubs" in the
container provided, rather than alongside as shown in figure 37 where a
"reckless''-picker was picking a bottom bed.
5. As a section of a bed is picked (figure 38) care should be taken
to harvest the mushrooms which have been knocked over during picking (figure
6. After the break has been completely picked (figure 40), remove all
knocked over pinheads, dead pins, and debris from the bed. This procedure
enhances the development of a uniform break of healthy mushrooms on the next
break (figure 41).
Pulling Mushrooms For Cannery Processing
Criteria previously mentioned for judging the maturity of mushrooms
for picking and cutting are equally applicable to mushrooms pulled for
cannery processing. Pulled mushrooms are removed from the bed with a
twisting motion. Twisting minimizes the amount of casing removed from the
bed and limits damage to adjacent immature mushrooms (figure 42). Several
mushrooms should be individually pulled and held in the hands before placing
them in the basket (figure 43). Mushrooms pulled for canning are not trimmed
at harvest time. Since the knife does not have to be held in one hand, both
hands may be used for pulling. Never pull a cluster of mushrooms (figure 44).
Such a practice causes excess amounts of casing to be removed and damages
adjacent immature mushrooms. It also interferes with the processing operation,
since the mushrooms then must be separated for the individual trimming opera-
tion. After pulling mature mushrooms from a section of the bed, the bed
should be clean (figure 45). Never allow knocked over mushrooms and mushroom
pieces to remain on the bed (figure 46). The knocked over mushrooms can
never be harvested and at times serve as centers for the spread of various .,
mushroom pathogens. When pulling mushrooms from first break clusters (figure
47) for cannery processing, the cluster should be steadied with one hand
while mature mushrooms are individually picked with the other hand (figure
48). The remaining undisturbed immature mushrooms (figure 49) will attain
proper size and maturity before being harvested which would not be the case
had the cluster been disturbed.
Mushroom harvesting requires finger dexterity and rapid judgment
regarding the stage of maturity on the part of the picker. Picking young
mushrooms means that the total pounds of mushrooms expected from a bed will
not be reached, and picking mushrooms too late means a decided decrease in
quality. Neither of these extremes is desirable, so it is wise to instruct
pickers periodically on which mushrooms to pick and how to pick them.
Incessant nagging about picking procedures is not appreciated by pickers,
but periodic instruction coupled with incentives for good picking practices
generally increase the effectiveness of your picking force.
SOURCES OF MUSHROOM SPAWN
Several seed companies list mushroom spawn for sale in their seed, .,
catalogs. Some of the ads are listed here.
Burgess Seed and Plant Company "Preplanted Home-grown Mushroom Farm.
Galesburg, Michigan 49053 Grow farm fresh mushrooms (Agaricus
bisporus) in any room of your home
during anytime of the year. Everything
necessary is supplied. Spawn is in the
soil and all you do is water and follow
easy directions. Recipes included. The
9 x 12" plastic pot is reversible for a
handy seed starter.
1970 Kit price $6.95."
W. Atlee Burpee Company -"Pure Culture Process Mushroom Spawn'
Philadelphia, Pennsylvania 19132 is easier to handle, growth more
vigorous, and results more certain.
One package plants 10 to 12 sq. ft.
S .'. Complete directions included. ,
1971 price per package $1.25
The mushroom is classified as a fungus which grows upon decaying
organic matter or as a parasite upon living vegetable growths. It is more
primitive both in structure anid method of reproduction than any of the
other vegetables. There is a great variety of mushrooms, but the only one
extensively grown commercially is Agaricus campestris.
Mushrooms grow best in a moist, dark, cool place that is well-
ventilated. The temperature should be below 750; 50 to 600 is ideal
because the growing period will be longer and the crop larger. Growth
will be slower at 45 or 500 but the bed will last longer. Should the
temperature go above 600, production will be speeded up, but the life
of the bed will be shorter.
Distribution and importance
Mushrooms may be grown almost anywhere as long as the proper growing
conditions are provided. As a source of food is the main use for mushrooms,
they may be eaten cooked in stews, soups, with meats, or as a side dish.
They may also be eaten raw, as when sliced in a tossed salad. Surplus mush-
rooms can be preserved by canning, freezing, or drying carefully on a tray
in the oven at a gentle heat. If they are to be frozen, it is important
to blanch them first in boiling water for one minute. Otherwise, they
will keep in the frozen state only a few weeks before turning black and
breaking down. .
Mushrooms can be grown successfully both indoors and outdoors. Most,
however, are grown indoors where such climatic.conditions as moisture and
temperature can be more easily controlled.
1. Soil mushrooms do not manufacture their own starches from
chlorophyll and sunlight. Therefore, they must have a prepared medium con-
taining organic matter and carbohydrates on which to grow. Horse manure
and wheat straw compost is a desirable medium, but a successful medium can
be formulated from ground corncobs, cotton seed meal, hay, green sand and
2. Planting mushrooms may be planted outdoors in heavily-mulched
areas which are rich in organic matter. Mushroom spawn can be obtained
from most large seed companies. Bits of spawn should be planted about 2
inches deep in the heavily-mulched areas. Under hedges and around trees
are good places for plantingas these areas receive much shade and retain
Indoors, mushrooms are grown in trays or beds. These may be obtained
from a seedsman or you may build your own. After filling the bed with the
planting medium, it should be kept well-moistened but not saturated. Spawn
may be obtained from a seedsman in a dried brick form which is broken into
1 inch pieces and planted at 10 inch intervals through the bed. The spawn
should be kept in a warm, moist place several days before planting. This
will stimulate growth after it has been placed in the bed. In 2 weeks the
spawn will have grown in white cottony threads or filaments through the top
3 inches of the compost. In 3 weeks, the first tiny white buttons begin to
appear all over the surface of the bed. This is the signal to cover the
bed with a 1-inch layer of screened and sterilized topsoil. The soil can
be sterilized by placing it in pans in a 2000 F. oven for 30 minutes. This
kills any weed seeds or unwanted fungi spores which may be present in the
3. Care and Problems whether indoors or outdoors, the planted area
should be sprinkled from time to time to keep it moist and to provide a humid
atmosphere for the growing mushrooms.
The only real problem in growing mushrooms occurs if dead buttons are
left in the bed. If left to decay, they may cause disease and kill out a
portion of the bed. After harvesting, the remaining stub or root should be
removed within a day or two, for the same reason. For this reason the bed
should be examined daily. No cultivation, such as by hoeing is needed.
This would disturb the tiny, threadlike roots called Mycelium.
4. Harvesting mature mushrooms are from one to two inches in
diameter. They mature rapidly and seem to come in recurrent bursts about a
week apart. Outdoors, mature mushrooms may appear after a rainfall. Care
should be exercised in pulling or cutting the mature mushrooms to disturb
the bed as little as possible.
Extracted by Susan Davis from:
Organic Gardening Feb. 1969
Organic Gardening Feb. 1966
Garden Farming Corbett p. 290-293