Laura Smith
Mushroom substrate is a bulk material that the mushroom mycelium uses for energy and nutrition. It is important to match the mushrooms with the correct substrate for the best chance of success. Common substrate recipes for growing mushrooms usually involve straw or hardwood sawdust, although there are many other options. For example, mushrooms will grow on various urban and agricultural waste products, from spent coffee grounds to banana leaves. Once the substrate is fully colonized by the mycelium, the mushrooms are ready to fruit.
| Characteristics | Values |
|---|---|
| Definition | A bulk material that the mushroom mycelium can use for energy and nutrition |
| Composition | Natural products such as wheat straw bedding, horse manure, hay, corn cobs, cottonseed hulls, poultry manure, brewer's grain, cottonseed meal, cocoa bean hulls, and gypsum |
| Additional supplements | Ground soybeans or seed meal |
| Casing layer | Mixture of peat moss and ground limestone |
| Nutrient requirements | Nitrogen (1-2%), magnesium, potassium, calcium, sulfur, phosphorus |
| pH level | Slightly acidic (5-6.5) |
| Pasteurization temperature | 150-185 °F |
| Sterilization temperature | Exceeding 250 °F |
| Containers | Large clear plastic bags, mason jars, buckets |
| Common substrates | Coffee grounds, straw, hardwoods (oak, beech, maple), soy hulls, hardwood sawdust |
| Spent substrate uses | Soil amendment, mulch, spread on newly seeded lawns |
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What You'll Learn
Pasteurization and sterilization
Mushroom cultivators use several methods to pasteurize or sterilize their mushroom substrates. The best method depends on the grower's experience, the mushroom species, and the type and amount of substrate.
Pasteurization is the process of heating a bulk substrate to a specific temperature range for a set period. It aims to reduce the number of harmful competitor organisms in a mushroom substrate before inoculating it with mushroom spawn. The temperature range for pasteurization is between 140°F to 185°F for 1.5 to 2 hours. It doesn't remove all contaminants but reduces the overall population of microbes, giving the mushroom species a head start.
There are two main types of pasteurization: heat pasteurization and cold pasteurization. Heat pasteurization is the most common method, using hot water or steam to heat the substrate. Cold pasteurization is a chemical-based process, usually using low-magnesium hydrated lime. It is cheap and effective but is considered a form of pasteurization rather than sterilization.
Sterilization, on the other hand, involves heating the substrate to extreme temperatures, typically above 250°F, under pressure, to completely eliminate any living or dormant contaminants within the substrate. Sterilization provides a clean slate, free from competition, but it also removes beneficial organisms that could assist in the mushroom cultivation process. Therefore, sterilized substrates may require the addition of beneficial microbes to prevent contamination.
The choice between pasteurization and sterilization depends on the specific requirements of the mushroom species and the grower's preferences. Pasteurization is generally more suitable for bulk substrate preparations, while sterilization is used for preparing spawn or when absolute control over the substrate's microbial environment is needed.
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Composition of spent mushroom substrate
Mushroom substrate is a material that the mycelium uses for energy, nutrition, and structure. The mycelium will need weeks or even months to decompose the substrate and spread throughout it. Once colonisation is complete, the substrate will be covered in mycelium and ready to fruit.
Spent mushroom substrate (SMS) is the soil-like material remaining after a crop of mushrooms. It is high in organic matter, which makes it desirable for use as a soil amendment or soil conditioner. It can be used to spread on top of newly seeded lawns, providing cover against birds and helping to hold water in the soil. However, it should not be used around plants that are sensitive to high salt content in the soil.
The composition of SMS varies depending on the raw materials included in the initial substrate, the mushroom species, and the cultivation technology. Common ingredients used to prepare substrate include wheat straw bedding containing horse manure, hay, corn cobs, cottonseed hulls, poultry manure, brewer's grain, cottonseed meal, cocoa bean hulls, and gypsum. Growers may also add ground soybeans or seed meal supplements later in the production cycle. On top of the substrate, farmers often apply a "casing" layer, which is a mixture of peat moss and ground limestone.
SMS has been found to improve soil structure and fertility, leading to increased crop production and contributing to the restoration of barren lands and degraded soils. It can be reused in new cultivation cycles, particularly for species of the genus Pleurotus and oyster mushrooms. However, in most studies, supplementation is required to adjust the nutrient content when SMS is used as the main substrate ingredient.
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Common substrates
One of the most common substrates is straw. It is cheap and effective, although it can be a little messy. Straw can be prepared with chemicals like peroxide or calcium hydroxide, or by fermenting the straw for at least a week. A preferred method is to use a heating method: cut straw into 3-4 inch pieces, shred the material, and pasteurize by submerging in 160-degree F water for an hour. After draining, the straw can be inoculated with mushroom spawn.
Another common substrate is hardwood, such as oak, beech, and maple. These are great for many types of mushrooms, especially when combined with a bran supplement. Soy hulls can also be mixed with hardwood sawdust to produce an effective substrate, especially for growing oysters.
Mushrooms will also grow on urban and agricultural waste products, such as coffee grounds and banana leaves. Coffee grounds are a good option as the brewing process pasteurizes them, and they can be obtained for free from coffee shops. The recipe is also simple: combine a kilogram of coffee grounds with 100 grams of mushroom spawn, and optionally add 20% straw for better air exchange and faster colonization.
Other common substrates include spent mushroom substrate, composted manure, and coir (a mix of ground-up coconut husk and shells).
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Preparing straw substrate
To prepare straw substrate, you can use a few different methods, including chemical treatments or fermentation. However, a simple heating method is both quick and organic. Here is a step-by-step guide:
Step 1: Prepare the Straw
Start by cutting your straw into three- or four-inch pieces. This step can be done more efficiently by using a weed whacker in a garbage bin to quickly shred the straw. For larger amounts, you may want to wash the straw with a small amount of dish soap to remove dust and debris. Ensure you thoroughly rinse off the soap before proceeding.
Step 2: Pasteurise the Straw
To pasteurise the straw, place it into a laundry bag, pillowcase, or nylon mesh bag and submerge it in water heated to 150-185°F (65.5-85°C) for about one hour. The temperature range for pasteurisation is between 150-180°F according to some sources. The higher the temperature, the shorter the pasteurisation time. For larger operations, you can use a 55-gallon drum and a butane burner.
Step 3: Drain and Cool the Straw
After pasteurisation, drain the straw well. When you squeeze a handful of straw, only a few drops of water should come out. Allow the straw to cool before proceeding to the next step.
Step 4: Inoculate with Spawn
Spread the straw on a clean surface and inoculate it with spawn. Exposure of wet straw to air destroys anaerobic organisms, creating an environment conducive for mushroom growth.
Alternative Methods
Instead of hot water pasteurisation, you can also use chemical treatments. One method involves soaking the straw in a lime water solution for 2-4 hours, draining it, and then immediately inoculating with spawn. Another method uses a peroxide solution, where the straw is soaked for 24 hours, drained, rinsed, and then inoculated.
Additionally, fermentation is another option for preparing straw substrate. For this method, submerge a bag of straw under water for 7-14 days, depending on the quantity. This process allows fermentation by anaerobic organisms and suppresses other microorganisms.
Tips for Success
When preparing straw substrate, ensure your straw is free of chemicals like glyphosate. You can supplement your straw with additional nutrients like rice flour, bran, molasses, or calcium. However, if you add flour or other nutritious supplements, you will need to sterilise the straw instead of pasteurising it.
Oyster mushrooms are an excellent choice for beginners, as they grow well on straw. Wheat straw, oat straw, and rice straw are all suitable options for substrate. If you live in a subtropical area with sugarcane, you can also use sugarcane bagasse.
Remember, the substrate's moisture and nutrition are crucial for mushroom growth, so always ensure your straw is adequately prepared and free of contaminants.
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Choosing the right substrate
A mushroom substrate is a bulk material that the mushroom mycelium uses for energy and nutrition. It needs to be dense in woody, fibrous materials like lignin, cellulose, and hemicellulose, which contain a lot of carbon, the main food source for the mycelium.
When choosing a substrate, there are a few key things to keep in mind. Firstly, it should have 1 to 2 percent nitrogen. Most substrates, like sawdust or straw, will need additional materials added to reach this level. Secondly, it should contain a small amount of magnesium, potassium, calcium, sulfur, and phosphorus. While most raw substrates have these minerals, the amounts can vary depending on their source, so you may need to experiment and supplement with additional minerals. Thirdly, the substrate should be slightly acidic, with a pH level of about 5–6.5.
There are various materials you can use as a substrate, each with its own preparation methods. Here are some common options:
- Straw: This is a cheap and effective option, commonly used to grow oyster mushrooms. It can be prepared in several ways, including chemical treatments or fermentation. A preferred method is to cut the straw into three or four-inch pieces, pasteurize it in 160°F water for an hour, drain it, and then inoculate it with mushroom spawn.
- Coffee grounds: Coffee grounds are a good option as the brewing process pasteurizes them, and they can often be sourced for free from coffee shops. Simply combine a kilogram of coffee grounds with 100 grams of mushroom spawn, and optionally add 20% straw for better air exchange and faster colonization.
- Hardwoods: Hardwoods such as oak, beech, and maple make for a great substrate, especially when combined with a bran supplement.
- Soy hulls and hardwood sawdust: Mixing soy hulls with hardwood sawdust produces a high-yielding substrate, especially for growing oysters.
- Coir: Coir is a mix of ground-up coconut husk and shells, which can be combined with vermiculite to create an effective substrate.
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Frequently asked questions
A mushroom substrate is a bulk material that the mushroom mycelium uses for energy and nutrition. Common recipes for growing mushrooms involve straw or hardwood sawdust, but there are many other options.
Examples of mushroom substrates include spent coffee grounds, banana leaves, coir (a mix of ground-up coconut husk and shells), and composted manure.
The substrate needs to have 1-2% nitrogen, a small amount of magnesium, potassium, calcium, sulfur, and phosphorus, and a pH level of 5–6.5. It should also be pasteurized or sterilized to reduce contaminants.
