Laura Smith
Mushrooms are fungi, which means they require different conditions and equipment to grow than plants. The process is highly technical and scientific, and it begins in a laboratory. The spores, or natural seeds of the mushroom, are inoculated into sterile cereal grains, which are incubated until they develop into spawn. This spawn is then mixed with a substrate—a nutritional balance of organic material—which acts as a growing medium. The mixture is transferred to trays or beds, and a casing of peat moss is spread over the top. Mushrooms are harvested by hand throughout a 16-35 day cycle. They can be grown indoors or outdoors, but they require sterile and moist conditions.
| Characteristics | Values |
|---|---|
| Mushroom type | White button mushroom, Agaricus bisporus |
| Growing method | Logs, large plastic bags, compost |
| Growing medium | Substrate |
| Substrate composition | Synthetic compost (wheat or rye straw, hay, crushed corn cobs, cottonseed meal, cocoa shells, gypsum) or manure-based compost (horse manure, poultry litter) |
| Spawn | Intentionally cultivated mycelium from a known species, often purchased from a supplier |
| Spawn form | Grain, sawdust, plug |
| Inoculation | Sterile conditions in a laboratory, where spores are inoculated into sterile cereal grains to create spawn |
| Phase I composting | Mixing and wetting ingredients, adding nitrogen supplements and gypsum, spraying water, releasing heat, ammonia, and carbon dioxide |
| Phase I duration | 6 to 14 days |
| Phase I compost characteristics | Chocolate brown colour, soft pliable straws, 68-74% moisture content, strong ammonia smell |
| Phase II composting | Not specified |
| Casing | Not specified |
| Pinning | Not specified |
| Cropping | Hand-harvested, matures at varying times |
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What You'll Learn
Mushrooms are fungi, not plants
Mushrooms are usually cultivated in sterile conditions in a laboratory. The spores are so tiny that they need to be handled by lab personnel, who inoculate sterile cereal grains with the spores and incubate them until they develop into a viable product. These grains become "spawn", which can then be sown like seeds. The grower then prepares the basic growing medium for mushroom production, which is called a substrate. The substrate is the growing mix for mushroom production, and without it, mushrooms will not grow.
There are two types of starting material generally used for mushroom substrate: synthetic compost consisting of wheat or rye straw, hay, crushed corn cobs, cottonseed meal, cocoa shells, and gypsum; or manure-based compost made from stable bedding from horse stables or poultry litter. This process converts plant and animal products into a mixture of decayed organic matter that is necessary for growing mushrooms. The substrate is placed in stacked wooden trays or beds, and the spawn is mixed in with a top layer, usually peat moss. From this point, it takes about three weeks to produce the first mushrooms for harvest.
One common method for growing mushrooms is inside large plastic bags filled with sterilized sawdust and wood chips. These bags retain moisture and help replicate natural conditions. However, this method produces a lot of plastic waste and requires a lot of energy for sterilization and climate maintenance. An alternative method that has been used for hundreds, if not thousands, of years is log growing. Logs provide a growing medium that is naturally sterile and, when responsibly sourced, is sustainable and self-replenishing.
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They grow from spores, not seeds
Mushrooms are fungi and require different conditions to grow than plants. They grow from spores, not seeds. These spores are so tiny that they cannot be handled by humans. In a laboratory setting, lab personnel will inoculate sterile cereal grains with the spores and incubate them until they develop into a viable product. This product is called "spawn", which can then be sown like a seed.
Spawn comes in three common forms: grain, sawdust, and plug. All organic material is broken down by fungi and bacteria. The job of a cultivator is to get the mycelium of the desired edible mushroom established before anything else can take hold. The higher the inoculation rate or amount of spawn added to the substrate, the faster the mycelium will grow through the substrate.
The substrate is the growing mix for mushroom production. Two types of starting material are generally used for mushroom substrate: synthetic compost consisting of wheat or rye straw, hay, crushed corn cobs, cottonseed meal, cocoa shells, and gypsum, or manure-based compost made from stable bedding from horse stables or poultry litter. This process converts plant and animal products into a mixture of decayed organic matter that is necessary for growing mushrooms.
The preparation of compost occurs in two steps: Phase I and Phase II composting. Phase I composting involves mixing and wetting the ingredients as they are stacked in a rectangular pile with tight sides and a loose centre. 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.
Phase I composting lasts from 6 to 14 days, depending on the nature of the material at the start and its characteristics at each turn. When compost temperatures are 155°F and higher, and ammonia is present, chemical changes occur which result in a food source exclusively used by the mushrooms. As a by-product of these chemical changes, heat is released, and the compost temperatures increase.
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Fungi thrive in damp, dark conditions
Mushrooms are fungi, and while they require different conditions and equipment to grow than plants, they can be cultivated commercially. Fungi have colonized nearly all environments on Earth, but they are most frequently found in cool, damp, dark places with a supply of decaying organic matter. This is because fungi are saprobes, meaning they decompose organic matter, releasing elements like nitrogen and phosphorus that are required in large quantities by biological systems. Fungi produce exoenzymes to digest nutrients, either releasing them into their substrate or keeping them bound to their cell walls.
Fungi thrive in temperatures ranging from 55 to 90 degrees Fahrenheit, though some species can survive in temperatures as low as 32 degrees or as high as 150 degrees. They prefer moist locations, but some fungi grow on dried grains. Mushrooms, in particular, tend to favour the dark, though rusts and mildews can grow in sunlight.
To replicate these conditions in a commercial setting, mushrooms are often grown in large plastic bags filled with sterilized sawdust and wood chips. This method helps retain moisture and mimic natural conditions, but it produces a lot of plastic waste. An alternative method is log growing, which has been used in China for centuries. Logs provide a growing medium that is naturally sterile and, when responsibly sourced, is sustainable and self-replenishing.
The process of growing mushrooms for commercial use is highly technical and scientific. It begins in a laboratory, where spores are inoculated into sterile cereal grains and incubated until they develop into spawn, which can then be sown. At this point, the grower prepares a substrate—a mixture of decayed organic matter that serves as a growing medium for the mushrooms. Common ingredients in mushroom substrate include wheat or rye straw, hay, crushed corn cobs, cottonseed meal, cocoa shells, gypsum, and manure-based compost.
Once the substrate is pasteurized, it is placed in stacked wooden trays or beds, and the spawn is mixed in with a top layer, usually peat moss. From here, it takes about three weeks to produce the first harvest of mushrooms. Throughout the growing period, temperature and humidity are carefully controlled, and each mushroom is harvested by hand.
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Mushrooms grow by expansion, not cell division
Mushrooms are fungi, and unlike plants, they require different conditions to grow. The process of mushroom farming is complex and scientific. It involves six steps: Phase I composting, Phase II composting, spawning, casing, pinning, and cropping. Phase I composting involves mixing and wetting the ingredients, which are stacked in a rectangular pile with tight sides and a loose centre. Water is sprayed onto the horse manure or synthetic compost, and nitrogen supplements and gypsum are added. Once the pile is formed, aerobic fermentation (composting) begins due to the growth of microorganisms. This process releases heat, ammonia, and carbon dioxide. After Phase I composting, which typically lasts between 6 to 14 days, the compost should have a chocolate brown colour, soft pliable straws, a moisture content of 68 to 74 per cent, and a strong ammonia smell.
Phase II composting involves further preparation of the compost, which will serve as the substrate or growing mix for mushroom production. The quality of the raw materials used in this phase influences the compost's performance in terms of spawn run and mushroom yield. Wheat straw, for example, should be stored under cover to prevent the growth of unwanted fungi and bacteria. Gypsum is added to minimise the greasiness of the compost and improve air permeation, which is essential for the composting process.
In the spawning phase, the pasteurised substrate is placed in stacked wooden trays or beds, and the spawn is mixed in. A top layer, usually peat moss, is applied. From this point, it takes about three weeks to produce the first mushrooms for harvest. Mushrooms mature at different times, so they are harvested by hand continuously for two to three weeks.
Contrary to the conventional growth by cell division, mushrooms, as fungi, grow by the expansion of their tubular cells. This growth occurs exclusively at the tips of filamentary structures called hyphae, which form fine, large networks in the ground known as mycelia. The hyphae extend by transporting construction materials on rails through the fungal cells to their outermost tips. Calcium concentration at the end of the cell defines when this happens. This growth mechanism allows fungi to grow rapidly, with some hyphae reaching lengths of several kilometres.
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They require a growth medium called substrate
Mushrooms are fungi and require different conditions to grow than plants. They require a growth medium called a substrate. This is a key ingredient in mushroom production. The substrate is the growing mix for mushroom production, just as soil is the growing medium for field crops.
There are two types of starting material generally used for mushroom substrate: synthetic compost or manure-based compost. Synthetic compost consists of wheat or rye straw, hay, crushed corn cobs, cottonseed meal, cocoa shells, and gypsum. Manure-based compost is made from stable bedding from horse stables or poultry litter. This process converts plant and animal products into a mixture of decayed organic matter that is necessary for growing mushrooms.
Straw is a very common substrate for home and beginning commercial growers. Oyster mushrooms grow very well on straw. The straw for oyster cultivation can be treated through fermentation, pasteurization, or a lime soak. Coffee grounds are another interesting substrate to use because they are effectively sterilized when they are used to produce coffee.
In the growing house, the pasteurized substrate is placed in stacked wooden trays or beds, and the spawn is mixed in. From this point, it takes about three weeks to produce the first mushrooms for harvest. Throughout the growing period, temperature and humidity are carefully controlled. Mushrooms mature at varying times, so picking by hand is continuous for two to three weeks. Every mushroom is harvested by hand.
The most common method for growing mushrooms commercially is inside large plastic bags filled with sterilized sawdust and wood chips. These bags retain moisture and help replicate natural conditions. However, this method leaves behind a lot of plastic waste and requires a lot of energy for sterilization and climate maintenance.
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Frequently asked questions
Mushrooms are fungi and require different conditions and equipment to grow than plants. They grow from fungal spores in damp, dark environments with high levels of decaying plant matter.
No, mushrooms do not require sunlight, which makes them ideal for indoor farming and popular with urban farmers.
Mushroom spawn is mixed with a substrate that provides a nutritional balance. This mixture is transferred to beds or trays, covered with casing to hold moisture, and then "pins" of mushrooms push through the casing.
The pinning stage occurs within 16-35 days. However, inoculated bolts can take up to 8 months to fruit, although this process can be accelerated by soaking them.
Mushrooms reproduce through a combination of asexual and sexual mechanisms. Asexual reproduction involves the production of spores by one parent only, which then disperse and form new colonies. Sexual reproduction involves the fusion of spores from two compatible types, introducing genetic variation.
