Basic Procedures for Agaricus Mushroom Growing
College of Agricultural Sciences
Agricultural Research and Cooperative Extension
Hippocrates first mentioned mushrooms when he wrote about their medicinal value in 400 B.C. The first mention of mushroom cultivation, distinct from a chance appearance in the field, was in 1652. Unfortunately, they were described as excellent for
«making into compresses for ripening boils» but not as good to eat. In 1707, a French botanist wrote about mushrooms as
«originating from a horse».
The mushroom is a fungus and is quite finicky about its food source. Mushrooms lack the ability to use energy from the sun. They are not green plants because they do not have chlorophyll. Mushrooms extract their carbohydrates and proteins from a rich medium of decaying, organicmatter vegetation. This rich organic matter must be prepared into nutrient-rich substrate composts that the mushroom can consume. When correctly made, this food may become available exclusively to the mushroom and would not support the growth of much else. At a certain stage in the decomposition, the mushroom grower stops the process and plants the mushroom so it becomes the dominant organism in that environment.
Many agricultural by-products are used to make mushroom substrate. Straw-bedded horse manure and hay or wheat straw are the common bulk ingredients.
«Synthetic» composts are those in which the prime ingredient is not straw-bedded horse manure. If bulk ingredients are high in nitrogen, other high-carbohydrate bulk ingredients — such as corncobs, cottonseed hulls, or cocoa bean hulls — are added to the mix. All compost formulas require the addition of nitrogen supplements and gypsum.
Improving community relations has led to alterations in the way the Phase I mushroom composting process is carried out. As urban areas encroach on rural farmland, residents have made odor-related complaints and legal battles have ensued, which suggest a need for more stringent odor-management practices.
Once Phase I is complete, the substrate will be filled into a system for Phase II substrate preparation and to grow the mushrooms. Phase II takes lace in one of three main types of mushroom-growing systems, depending on the type of production system used. The difference in the mushroom-growing systems is the container in which the crop is processed and grown.
Phase II composting is the second step of compost substrate preparation. The first objective of Phase II is to pasteurize the composted substrate. The composted substrate is pasteurized to reduce or eliminate the bad microbes such as insects, other fungi, and bacteria. This is not a complete sterilization but a selective killing of pests that will compete for food or directly attack the mushroom. At the same time, this process minimizes the loss of good microbes.
A desirable mycelial culture is pure—free of contaminants and of sectoring of other abnormalities. Contaminants include other fungi, bacteria, or insects growing on or infesting the culture media along with the desired mycelial culture. When a culture is first obtained, it should be transferred several times to fresh media to check for any form of contamination.
The process of making spawn remains much the same as Penn State professor emeritus Dr. Sinden first developed in the 1930s. Grain is mixed with a little calcium carbonate, then cooked, sterilized, and cooled. Small pieces of pure-culture mycelium are placed in small batches on the grain.
On bed farms, spawn and supplement are broadcast over the surface of the substrate. Uniformity of this distribution is critical to achieve even spawn growth and temperatures. On tray or bulk farms, spawn is usually metered into the substrate during the mixing operation. Spawning is the cleanest operation performed on a mushroom farm. All equipment, baskets, tools, and so forth should be thoroughly cleaned and disinfected before spawning.
The compost has to provide the mushroom mycelium with a smorgasbord of food. Not only is ligninhumus complex and cellulose important, but protein, fat, and oils are also important. A good analogy is protein serves as the mushroom’s
«steak», carbohydrates its »potatoes», and lipids
(fats and oils) its »butter». Like people, mushrooms should eat a balance of all these food types. The main source of »steak and butter» for the mushroom is from Phase II microbes.
The only method of forcing mushroom mycelia to change from the vegetative phase to a reproductive state is to apply a cover of a suitable material — called the casing layer — on the surface of the spawned compost. The function of a casing layer is to trigger the mushrooms to switch from a vegetative growth to a reproductive or fruiting growth. The mechanism that initiates the spawn to change from vegetative to reproductive growth is unknown, though several theories have been presented. The casing also functions to supply and conserve moisture for the mushrooms and their rhizomorphs
(thicker mushroom mycelia) and acts to transport dissolved nutrients to the mushrooms.
Fully colonized spawn run substrate is used to introduce mycelia into the casing layer. This is often used to improve crop uniformity, crop cycling, mushroom quality, and yields
(Figure 14). Spawn run compost at casing
(CAC) is used to inoculate the casing during the mixing or application of the casing. CAC is now produced much like spawn — in aseptic conditions — by those who produce and supply spawn to growers. This process is called casing inoculum
(CI).
The moisture content of the casing often determines the uniformity of the casing depth. Casing, both by equipment and by hand, becomes more difficult as the casing material increases in moisture. Peat moss casing will lump up or adhere to the different parts of the equipment, making the flow of the material uneven.
Mushroom initials develop after rhizomorphs have formed in the casing. The initials are extremely small but can be seen as clumps on a rhizomorph. As these structures grow and expand, they are called primordia or pins. Mushroom pins continue to grow larger through a prebutton stage and ultimately enlarge to mature mushrooms. Mushroom harvesting begins 15–21 days after casing, which is normally 10–12 days after flushing and 7–8 weeks after composting started. The cultural practices used during pin development and cropping include the management of air and compost temperatures and CO
2 content of room air, and is often dependent on the strain and number of pins the grower wishes to form and develop.
Mushrooms are harvested over a 2–4-day period in a 7–10-day cycle called flushes or breaks. When mature mushrooms are picked, an inhibitor to mushroom development is removed and the next flush moves toward maturity. Timing of the breaks or flushes is managed by control of the watering, CO
2, and temperatures. The first two flushes account for the majority of the total yield, with the subsequent flushes tapering off to relatively low levels of production. Mushrooms are harvested by hand and are picked at a time before the cap becomes soft, indicating the mushroom is past prime fresh-quality potential. Harvesting rates depend mainly on the amount of crop on the beds and size of the mushrooms. Rates vary from 30 to 80 lbs/hour.
When a house becomes unproductive, the crop is usually terminated. Before removing the spent substrate from the mushroom house, the grower
«pasteurizes» it with steam to kill any diseases, pests or other biological activity that could interfere with a neighboring house or subsequent crop. The steaming-off procedure is accomplished by maintaining a compost temperature of 140–150ºF
(60–70ºC) for anywhere from 8 to 24 hours. The spent compost should be removed from the farm to reduce the chances of contaminating the subsequent mushroom crops at the farm.