Michael Davis
Mushroom compost, also known as mushroom substrate, is the medium in which mushrooms are grown. It is a blend of natural products such as wheat straw, hay, corn cobs, cottonseed hulls, poultry or horse manure, and gypsum. After mushrooms are harvested, the substrate is often sold as spent mushroom compost (SMC) or spent mushroom substrate (SMS). This spent substrate is high in organic matter and can be used as a soil amendment or conditioner, improving water retention and breaking down clay-like soils. It can also be pasteurized and used to grow a new batch of mushrooms. Mushroom blocks are another form of mushroom compost, which can be added to an existing compost pile to increase the decomposition rate and provide additional nutrients.
| Characteristics | Values |
|---|---|
| What is mushroom compost? | A by-product of mushroom farming, it is the medium in which mushrooms are grown. |
| Composition | Wheat straw, hay, corn cobs, cottonseed hulls, poultry/chicken manure, brewer's grain, cottonseed meal, cocoa bean hulls, gypsum, and horse manure. |
| Pasteurization | Pasteurized prior to use to ensure no bacteria is present. |
| Commercial blends | Wheat straw, gypsum, and chicken or horse manure. |
| Preparation | Large bales of wheat straw are dunked in water, then run through a chipper to make it into a finer particulate. |
| Use | Used to grow mushrooms commercially or in large agricultural applications. |
| Re-use | Can be used as a soil amendment or soil conditioner. |
| Mushroom blocks | Can be added to compost piles to break down organic matter quickly, resulting in rich soil. |
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What You'll Learn
Pasteurisation: kill weed seeds, insects and pathogens
Pasteurisation is a critical step in preparing mushroom substrates for optimal growth. It involves heating the substrate to a specific temperature range for a set period to kill weed seeds, insects, and pathogens. Unlike sterilisation, which eradicates all living organisms within the substrate, pasteurisation aims to preserve beneficial microorganisms, which play a vital role in protecting against invasive species and aiding the breakdown of complex materials into nutrients that mushrooms can easily absorb.
There are two main types of pasteurisation methods: heat and cold. Hot water pasteurisation, which involves submerging the substrate in hot water between 149 and 167°F (65 and 75°C) for one to two hours, is more effective at killing heat-sensitive competitors while retaining beneficial heat-tolerant bacteria. However, it can be expensive for bulk substrates. To pasteurise using this method, bring the water to a boil and then turn down the heat to reach the desired temperature range. Practise will help you determine the right setting on your stove to maintain the correct temperature, but initially, it is best to use a thermometer.
Cold pasteurisation, on the other hand, is often safer, easier, and more energy-efficient. It is ideal for large quantities of bulk substrate as it does not require heating large volumes of water or maintaining high temperatures. One popular cold pasteurisation method is natural fermentation, which involves submerging straw in non-chlorinated water for around a week. During this time, anaerobic microorganisms multiply and break down the substrate, killing oxygen-dependent organisms like fungal spores. Cold water bath pasteurisation, which involves soaking the substrate in a solution for 12 to 24 hours, is another effective method. This solution can include additives like lime, wood ash, soap, chlorine, or vinegar. The duration of pasteurisation is crucial for killing harmful pathogens and preserving beneficial microbes.
Regardless of the method chosen, successful pasteurisation is a major milestone in mushroom cultivation. However, it is equally important to handle the substrate with care after pasteurisation to avoid contamination. Always use sterile equipment and work in a clean area when handling pasteurised substrates. Additionally, allow the substrate to cool down to room temperature before inoculating it with mushroom spawn to avoid killing the mycelium.
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Ingredients: wheat straw, gypsum, horse manure, etc
Wheat straw is a common ingredient in mushroom compost, often used as bedding for horses. It is important to soak the straw in water and control the moisture content—not too wet or too dry. The straw should be soft and pliable, and the lumps should break apart easily.
Gypsum is another important ingredient, added early in the process at 70–100 lbs per ton of dry ingredients. It can be tricky to find but is available online.
Horse manure is a key ingredient in mushroom compost, providing nutrients for mushroom growth. It is often mixed with gypsum and added to the straw. It is important to note that manure should be sterilized before use due to the presence of bacteria and other microbial life.
Other ingredients that can be used in mushroom compost include hay, corncobs, poultry manure, and horse stable bedding. The ingredients may vary depending on the region, but these are some of the most common components used in the process.
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Uses: soil amendment, mulch, planting mix
Mushroom compost is a popular soil amendment that can enhance plant growth, improve soil structure, and provide essential nutrients for your garden. It is a by-product of the mushroom farming industry, made from the spent mushroom substrate used in commercial production. The substrate is composted for about 30 days at 160 degrees Fahrenheit to kill weed seeds, pests, and disease pathogens. It is then steam-pasteurized at 140 degrees Fahrenheit to kill any remaining pests and pathogens. The sterilized substrate is then sold as a soil conditioner and mulch for ornamental and vegetable gardens.
Mushroom compost can be used as a soil amendment in container gardening. Mix it with potting soil or other organic materials to improve soil structure, increase water retention, and provide plant nutrients. It can be applied as a top dressing to help retain moisture, suppress weeds, and slowly release plant nutrients. However, it is important to avoid smothering plant stems or covering foliage when applying it as a mulch. Additionally, mushroom compost should not be used as a mulch for acid-loving or ericaceous plants, such as rhododendrons, camellias, and heather, as the higher pH level can make it difficult for these plants to access the nutrients they need from the soil.
Mushroom compost is also an excellent addition to a planting mix or raised bed medium. The straw content provides great organic material to improve water retention and will continue to break down over time. It is relatively low in nutrients as the mushrooms that were previously grown in the substrate have consumed much of the available nitrogen. However, it is still a valuable resource for gardeners, providing a blend of nutrients, including nitrogen, phosphorus, potassium, trace minerals, and organic matter.
Mushroom compost can be purchased fresh or aged/cured. If you buy it fresh, it needs curing before adding it to your soil. Rain and snowfall help leach excess salts from the substrate, and any pesticide residue from mushroom growing will also decompose. Aged, cured mushroom compost can be applied any time in the spring or summer, and it is most effective when the soil is fairly dry. This helps to avoid compacting the soil while tilling in amendments.
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Benefits: eco-friendly, reduces waste, improves soil moisture
Mushroom compost is an eco-friendly, waste-reducing, and soil-moisture-improving method that can be used in gardens and farms. It is made from the spent mushroom substrate, which is the residual growing medium used to cultivate mushrooms. This substrate is usually a blend of natural products, including wheat straw, hay, corn cobs, cottonseed hulls, poultry manure, and other agricultural byproducts.
The process of creating mushroom compost involves pasteurizing and composting these materials to eliminate weed seeds and harmful pathogens, creating a sterile and nutrient-rich environment for mushrooms to grow. The pasteurization process also kills any pests or pathogens that may be present, ensuring the substrate is clean and safe. This is especially important for spent mushroom substrate, which has already been used to grow mushrooms and may contain residual nutrients.
Using mushroom compost offers several benefits. Firstly, it is an eco-friendly and sustainable practice as it repurposes waste materials that would otherwise be discarded, reducing the environmental footprint. Additionally, mushroom compost is excellent for improving soil structure and moisture retention. The straw content in the compost helps break up clay-like soils and improves water retention, making it a popular choice for lawns and turf conditioning.
Mushroom compost is also beneficial for plants as it provides additional nutrients that support healthy growth. The compost contains organic matter, moisture, nitrogen, phosphate, and potash, which are essential for plant development. Furthermore, mushroom compost can be used as a mulch to suppress weeds and slowly release plant nutrients, providing long-lasting benefits to the soil.
Overall, composting with mushroom blocks or spent mushroom substrate is an effective way to improve soil health, reduce waste, and enhance moisture retention. It is a simple and environmentally friendly practice that can be easily incorporated into gardening and agricultural practices.
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Drawbacks: high salt content, not for seedlings
Mushroom compost is a by-product of mushroom farming and can be used as a fertilizer and organic soil amendment for many plants. The substrate in which mushrooms are grown is no longer suitable for growing mushrooms after some time, but it is still valuable for gardeners. The mushroom substrate contains hay, straw, poultry or horse manure, and crop residues such as corn cobs and cocoa shells. The exact composition of the growth substrate varies from grower to grower.
One drawback of mushroom compost is its high salt content. The general public uses the term salt to mean table salt, or sodium chloride. However, the salt content in mushroom compost is not sodium chloride, but rather calcium sulfate, or gypsum. Gypsum is added to the mushroom compost to provide sulfur, a nutrient required by plants. While this is beneficial for some plants, it can be harmful to others. Plants that are sensitive to high salt content in soils include azaleas, rhododendrons, camellias, and other members of the Ericaceae family. Therefore, it is important to avoid using fresh spent substrate around these plants.
To reduce the salt content of mushroom compost, it is recommended to let the compost mature before adding it to the soil. This allows the salt to break down and reduces the risk of harming salt-sensitive plants. Additionally, weathering the spent substrate for 6 months or longer can help reduce salt content and make it suitable for use in all gardens and with most plants. Obtaining spent substrate in the fall and winter and allowing it to weather will make it ready to use in the spring.
Another drawback of mushroom compost is that it is not suitable for seedlings. The high salt content in mushroom compost can impact germination and harm young plants. The compost is also relatively low in nutrients, as the mushrooms that were previously grown in it have consumed a lot of the immediately available nitrogen. Therefore, it is recommended to mix mushroom compost with 80% soil to create a suitable growing medium for seedlings.
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Frequently asked questions
Mushroom compost is a by-product of mushroom farming. It is the soil-like material remaining after a crop of mushrooms have been harvested.
Mushroom substrate is made of wheat straw bedding containing horse manure, hay, corn cobs, cottonseed hulls, poultry manure, brewer's grain, cottonseed meal, cocoa bean hulls and gypsum.
First, pasteurise the substrate with steam to kill any pests or pathogens. Then, compost the substrate for about 30 days at 160 degrees Fahrenheit. Next, steam-pasteurise the substrate at about 140 degrees Fahrenheit. Finally, inoculate the medium with mushroom spores.
Mushroom compost can be used as a plant fertiliser and soil amendment to benefit your plants. It can be used to fertilise lawns, as a top-dressing for newly seeded lawns, and around most plants. However, do not use mushroom compost on salt-sensitive plants such as azaleas, rhododendrons, camellias, and other members of the Ericaceae family.
