This tek is for large scale
composting but could be modified for a smaller scale operation.
Mushroom farming consists of six steps, and although the divisions are somewhat arbitrary, these steps
identify what is needed to form a production system.
The six steps are Phase I composting, Phase II composting, spawning, casing, pinning, and cropping.
These steps are described in their naturally occurring sequence, emphasizing the salient features within
Compost provides nutrients needed for mushrooms to grow. Two types of material are
generally used for mushroom compost, the most used and least expensive being wheat straw-bedded
Synthetic compost is usually made from hay and crushed corncobs, although the term
often refers to any mushroom compost where the prime ingredient is not horse manure. Both types of
compost require the addition of nitrogen supplements and a conditioning agent, gypsum.
The preparation of compost occurs in two steps referred to as Phase I and Phase II composting. The
discussion of compost preparation and mushroom production begins with Phase I composting.
1. Phase I: Making Mushroom Compost
This phase of compost preparation usually occurs outdoors although an enclosed
building or a structure with a roof over it may be used. A concrete slab, referred to
as a wharf, is required for composting. In addition, a compost turner to aerate and
water the ingredients, and a tractor-loader to move the ingredients to the turner is
needed. In earlier days piles were turned by hand using pitchforks, which is still an
alternative to mechanized equipment, but it is labor intensive and physically
Phase I composting is initiated by mixing and wetting the ingredients as they are stacked in a
rectangular pile with tight sides and a loose center. Normally, the bulk ingredients are put through a
compost turner. Water is sprayed onto the horse manure or synthetic compost as these materials move
through the turner. Nitrogen supplements and gypsum are spread over the top of the bulk ingredients and
are thoroughly mixed by the turner. Once the pile is wetted and formed, aerobic fermentation
(composting) commences as a result of the growth and reproduction of microorganisms, which occur
naturally in the bulk ingredients. Heat, ammonia, and carbon dioxide are released as by-products during
this process. Compost activators, other than those mentioned, are not needed, although some organic
farming books stress the need for an "activator."
Mushroom compost develops as the chemical nature of the raw ingredients is converted by the activity of
microorganisms, heat, and some heat-releasing chemical reactions. These events result in a food source
most suited for the growth of the mushroom to the exclusion of other fungi and bacteria. There must be
adequate moisture, oxygen, nitrogen, and carbohydrates present throughout the process, or else the
process will stop. This is why water and supplements are added periodically, and the compost pile is
aerated as it moves through the turner.
Gypsum is added to minimize the greasiness compost normally tends to have. Gypsum increases the
flocculation of certain chemicals in the compost, and they adhere to straw or hay rather than filling the
pores (holes) between the straws. A side benefit of this phenomenon is that air can permeate the pile
more readily, and air is essential to the composting process. The exclusion of air results in an airless
(anaerobic) environment in which deleterious chemical compounds are formed which detract from the
selectivity of mushroom compost for growing mushrooms. Gypsum is added at the outset of composting
at 40 lbs. per ton of dry ingredients.
Nitrogen supplements in general use today include brewer‰s grain, seed meals of soybeans, peanuts,
or cotton, and chicken manure, among others. The purpose of these supplements is to increase the
nitrogen content to 1.5 percent for horse manure or 1.7 percent for synthetic, both computed on a dry
weight basis. Synthetic compost requires the addition of ammonium nitrate or urea at the outset of
composting to provide the compost microflora with a readily available form of nitrogen for their growth and
Corn cobs are sometimes unavailable or available at a price considered to be excessive. Substitutes for
or complements to corn cobs include shredded hardwood bark, cottonseed hulls, neutralized grape
pomace, and cocoa bean hulls. Management of a compost pile containing any one of these materials is
unique in the requirements for watering and the interval between turning.
The initial compost pile should be 5 to 6 feet wide, 5 to 6 feet high, and as long as necessary. A
two-sided box can be used to form the pile (rick), although some turners are equipped with a "ricker" so
a box isn‰t needed. The sides of the pile should be firm and dense, yet the center must remain loose
throughout Phase I composting. As the straw or hay softens during composting, the materials become
less rigid and compactions can easily occur. If the materials become too compact, air cannot move
through the pile and an anaerobic environment will develop.
Turning and watering are done at approximately 2-day intervals, but not unless the pile is hot (145° to
170°F). Turning provides the opportunity to water, aerate, and mix the ingredients, as well as to relocate
the straw or hay from a cooler to a warmer area in the pile, outside versus inside. Supplements are also
added when the ricks are turned, but they should be added early in the composting process. The number
of turnings and the time between turnings depends on the condition of the starting material and the time
necessary for the compost to heat to temperatures above 145°F.
Water addition is critical since too much will exclude oxygen by occupying the pore space, and too little
can limit the growth of bacteria and fungi. As a general rule, water is added up to the point of leaching
when the pile is formed and at the time of first turning, and thereafter either none or only a little is added
for the duration of composting. On the last turning before Phase II composting, water can be applied
generously so that when the compost is tightly squeezed, water drips from it. There is a link between
water, nutritive value, microbial activity, and temperature, and because it is a chain, when one condition
is limiting for one factor, the whole chain will cease to function. Biologists see this phenomenon
repeatedly and have termed it the Law of Limiting Factors.
Phase I composting lasts from 7 to 14 days, depending on the nature of the
material at the start and its characteristics at each turn. There is a strong ammonia
odor associated with composting, which is usually complemented by a sweet,
moldy smell. When compost temperatures are 155°F and higher, and ammonia is
present, chemical changes occur which result in a food rather exclusively used by
the mushrooms. As a by-product of the chemical changes, heat is released and the
compost temperatures increase. Temperatures in the compost can reach 170° to 180°F during the
second and third turnings when a desirable level of biological and chemical activity is occurring. At the
end of Phase I the compost should: a) have a chocolate brown color; b) have soft, pliable straws, c) have
a moisture content of from 68 to 74 percent; and d) have a strong smell of ammonia. When the moisture,
temperature, color, and odor described have been reached, Phase I composting is completed.
2. Phase II: Finishing the Compost
There are two major purposes to Phase II composting. Pasteurization is necessary to kill any insects,
nematodes, pest fungi, or other pests that may be present in the compost. And second, it is necessary
to remove the ammonia which formed during Phase I composting. Ammonia at the end of Phase II in a
concentration higher than 0.07 percent is often lethal to mushroom spawn growth, thus it must be
removed; generally, a person can smell ammonia when the concentration is above 0.10 percent.
Phase II takes place in one of three places, depending on the type of production system used. For the
zoned system of growing, compost is packed into wooden trays, the trays are stacked six to eight high,
and are moved into an environmentally controlled Phase II room. Thereafter, the trays are moved to
special rooms, each designed to provide the optimum environment for each step of the mushroom
growing process. With a bed or shelf system, the compost is placed directly in the beds, which are in
the room used for all steps of the crop culture. The most recently introduced system, the bulk system, is
one in which the compost is placed in a cement-block bin with a perforated floor and no cover on top of
the compost; this is a room specifically designed for Phase II composting.
The compost, whether placed in beds, trays, or bulk, should be filled uniformly in
depth and density or compression. Compost density should allow for gas
exchange, since ammonia and carbon dioxide will be replaced by outside air.
Phase II composting can be viewed as a controlled, temperature-dependent,
ecological process using air to maintain the compost in a temperature range best
suited for the de-ammonifying organisms to grow and reproduce. The growth of these thermophilic
(heat-loving) organisms depends on the availability of usable carbohydrates and nitrogen, some of the
nitrogen in the form of ammonia.
Optimum management for Phase II is difficult to define and most commercial growers tend toward one of
the two systems in general use today: high temperature or low temperature.
A high temperature Phase II system involves an initial pasteurization period during which the compost
and the air temperature are raised to at least 145°F for 6 hours. This can be accomplished by heat
generated during the growth of naturally occurring microorganisms or by injecting steam into the room
where the compost has been placed, or both. After pasteurization, the compost is re-conditioned by
immediately lowering the temperature to 140°F by flushing the room with fresh air. Thereafter, the
compost is allowed to cool gradually at a rate of approximately 2° to 3°F each day until all the ammonia
is dissipated. This Phase II system requires approximately 10 to 14 days to complete.
In the low temperature Phase II system the compost temperature is initially increased to about 126°F
with steam or by the heat released via microbial growth, after which the air temperature is lowered so the
compost is in a temperature range of 125° to 130°F range. During the 4 to 5 days after pasteurization,
the compost temperature may be lowered by about 2°F a day until the ammonia is dissipated.
It is important to remember the purposes of Phase II when trying to determine the proper procedure and
sequence to follow. One purpose is to remove unwanted ammonia. To this end the temperature range
from 125° to 130°F is most efficient since de-ammonifying organisms grow well in this temperature
range. A second purpose of Phase II is to remove any pests present in the compost by use of a
At the end of Phase II the compost temperature must be lowered to approximately 75° to 80°F before
spawning (planting) can begin. The nitrogen content of the compost should be 2.0 to 2.4 percent, and the
moisture content between 68 and 72 percent. Also, at the end of Phase II it is desirable to have 5 to 7
lbs. of dry compost per square foot of bed or tray surface to obtain profitable mushroom yields. It is
important to have both the compost and the compost temperatures uniform during the Phase II process
since it is desirable to have as homogenous a material as possible.
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