Michael Davis
Mushroom farming is a complex yet rewarding endeavour that has gained popularity due to the increasing demand for locally sourced and sustainable food. It involves cultivating mushrooms on a small plot of land, typically in a controlled indoor environment known as a grow room. This environment needs to be dark, humid, and well-ventilated to prevent the mushrooms from drying out or becoming susceptible to bacterial growth. The growing medium, which can be straw or soil compost, is inoculated with mushroom spores, eventually developing into the final mushroom product. The process, from composting to harvest, takes around 14 weeks and includes phases of composting, spawning, casing, pinning, and cropping.
| Characteristics | Values |
|---|---|
| Mushroom growing process | Six main steps: Phase I and Phase II composting, spawning, casing, pinning, and cropping |
| Spawn | Made from stored culture (millet, rye, wheat) |
| Compost preparation | Reduce problems during spawn-growing period |
| Pinning | Affects crop quality and final yield; requires fresh air and carbon dioxide content of 0.08% or lower |
| Harvest | Begins 15-21 days after casing; picked over 2-4 days in a 7-10 day cropping cycle |
| Post-harvest | Pasteurization (steam-off) prevents pests and pathogens from contaminating subsequent crops |
| Growing environment | Indoor controlled environment with optimal temperature and humidity |
| Ideal humidity level | 80-90% to prevent stunted growth or bacterial growth |
| Ventilation | Necessary for proper air circulation and humidity regulation |
| Growing medium | Straw or soil compost inoculated with mushroom spores |
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What You'll Learn
Mushroom substrate preparation
The first step in substrate preparation is selecting the appropriate substrate for the specific mushroom species being cultivated. Different mushroom species have different preferences, and matching the substrate to the mushroom type is crucial for optimal results. For instance, wood-based substrates are ideal for reishi, lion's mane, and maitake mushrooms, while oyster mushrooms can grow on a wide range of substrates, including straw and even cardboard.
Once the substrate is selected, it needs to be prepared correctly. This includes adding water and, if necessary, supplementing it with additional nutrients. For example, straw is a popular substrate choice that can be prepared in various ways, such as pasteurisation or fermentation. Pasteurisation can be achieved through different methods, including heating, cold water lime pasteurisation, or substrate fermentation. The heating method involves cutting the straw into three to four-inch pieces, submerging them in water, and heating them to a specific temperature range for a set duration.
After the substrate is prepared, it needs to be sterilised or pasteurised to eliminate any competing mould or bacteria. This step ensures that the desired species of mushroom has the best chance of taking hold and establishes a clean slate for the mushroom mycelium to grow. Commercial growers often pack the substrate into large clear plastic bags, while home growers may use smaller containers like mason jars or buckets.
Finally, once the substrate is in its final container and properly sterilised or pasteurised, it is ready for inoculation with mushroom spawn or spores to initiate the growing process. This step marks the beginning of the mushroom's development within the carefully prepared substrate.
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Spawning
To produce spawn, a high-quality mushroom strain is selected and cultivated in a nutrient-rich medium, such as potato dextrose agar (PDA), to create the "mother culture". This serves as the source of mycelium for further propagation. The substrate, typically grains like wheat, millet, or sorghum, or materials like sawdust, is then prepared and sterilised to eliminate contaminants before inoculation. Maintaining sterility throughout this process is critical to ensure high-quality spawn and prevent contamination by bacteria, moulds, or other fungi that can lead to poor yields or crop failure.
There are different types of spawn, each suitable for different cultivation methods. Plug spawn, for example, involves growing mycelium on wooden dowels or plugs that are then hammered into freshly cut hardwood logs. Grain spawn, on the other hand, is commonly used for commercial indoor mushroom grows and is made from grains like millet or wheat. It is important to select the appropriate type of spawn for your specific cultivation method and mushroom variety.
Additionally, the health of the spawn is crucial. Healthy and white spawns are considered best for the cultivation process. Maintaining the purity of spawns is essential to prevent contamination by bacteria, fungi, or viruses, which can lead to the deterioration of the yield. Proper techniques must be practised for spawn preparation to ensure successful mushroom cultivation.
For those interested in growing their own mushrooms at home, there are DIY spawn techniques available, such as the stem butt method. This method is simple, low-tech, and inexpensive, but it may have lower yields and be less reliable. It involves using the stems of fresh oyster mushrooms, which can be purchased from grocery stores, and growing them on cardboard. While cardboard does not provide as many nutrients as grain, it can still support mushroom growth.
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Casing
The casing layer is typically about 1/2-inch to 1-inch thick and is placed on top of the spawned compost. It is essential to ensure the casing layer doesn't dry out completely, as this can cause the pins to abort. The casing must supply sufficient water to the mushroom mycelium and developing sporophores, with an optimum casing matric potential (Ψm) of about -8 kPa.
There are various materials used for the casing layer, each with its own water retention properties and impact on mushroom yield and quality. Traditional peat-based casings, such as Irish wet-dug peat, have been commonly used for button mushroom cultivation. However, due to environmental concerns, alternative materials like bark, spent mushroom substrate, coconut fibre, paper by-products, and green waste compost have been explored. While some of these alternatives have shown promising results as partial peat substitutes, none have matched the yield and quality of pure peat casings.
To pasteurize the casing layer without altering its moisture content, it can be placed in a mushroom grow bag and simmered for 45-60 minutes, reaching a temperature of 65-80°C. This process helps prevent contamination and ensures optimal conditions for mushroom growth.
Additionally, a technique called top dressing with casing inoculum (CI) has been developed to shorten the crop cycle by up to a week. By applying CI to the compost early, a more immediate mycelial connection is established, reducing the time required for the mycelium in the CI to connect to the compost. However, early casing can lead to compost overheating if applied before spawn run temperatures have peaked and begun to decline.
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Pinning
During pinning, mushrooms use cell division to form all the cells they need to produce the final mature mushroom. Once pinning is complete, they no longer use cell division to grow. Instead, they flood the existing cells with water and nutrients, allowing them to expand rapidly. Not all the mushroom pins will grow into mature mushrooms. The fungus selects the healthiest, most viable pins, and these expand to become mature mushrooms.
Before pinning, a large portion of the mushroom's life cycle happens. The first stage of pinning looks like tiny bumps starting to form on the surface of the mycelium covering the mushroom substrate. The mycelium clumps together to form hyphal knots, which cause these bumps. If your mycelium has completely colonized the substrate, begins to get denser, and forms white blobs or bumps, you know the pinning process is beginning.
To initiate pinning, you must signal to the mycelium that it has reached the surface by providing light and reducing CO2 levels. You must also simulate autumn-like conditions to indicate that it is a suitable environment for fruiting. Lower temperatures and high humidity help with this. Depending on the type of mushrooms you are growing and the method you're using, initiating pinning could involve different steps. If you're growing mushrooms in bags, it may involve cutting a hole or opening the top of the bag. For shiitake mushrooms, you should remove the grow bag and mist the colonized substrate.
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Cropping
Before cropping, it is important to ensure that the mushrooms have adequate growing conditions and proper environmental conditions. Mushrooms are grown in a controlled environment, typically in a dark and humid space. The ideal humidity level for growing mushrooms is between 80-90%. This range is necessary to keep the growing environment moist and prevent the mushrooms from drying out. If the humidity levels are too low, the mushrooms will not grow correctly and will become stunted. On the other hand, if the humidity levels are too high, the mushrooms will become too moist, leading to bacterial growth, which can destroy the entire crop. To maintain the correct humidity levels for growing mushrooms, it is essential to keep the growing area well-ventilated. Proper air circulation will help to regulate the humidity levels and prevent the growth of harmful bacteria. Additionally, the use of a humidifier or misting system can help maintain the correct humidity levels in the growing area. It is also essential to monitor the humidity levels regularly to ensure that they remain within the ideal range.
After cropping, it is important to pasteurize the spent mushroom substrate with steam to ensure that there are no pests or disease-causing pathogens that can contaminate neighbouring or subsequent crops. The mushroom grow room should also be steamed after the substrate is removed, and the beds should be washed down. When steaming off a room with a substrate, the temperature should be no less than 150°F for at least 12 hours.
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Frequently asked questions
Mushroom cropping involves six main steps: Phase I and Phase II composting, spawning, casing, pinning, and cropping.
Mushrooms grow best in a controlled environment, typically in a dark and humid space with an ideal humidity level between 80-90%.
Mushroom harvest begins 15 to 21 days after casing, which is 7 to 8 weeks after composting starts. Mushrooms are picked over a period of 2 to 4 days in a 7- to 10-day cropping cycle.
