Sarah Brown
Mushrooms require a substrate—a material that provides nutrition and structure—to grow, much like how plants need soil. The type of substrate you use depends on the species of mushroom you want to grow, and different mushrooms have evolved to digest specific materials in nature. For example, oyster mushrooms grow well in pasteurised straw, while shiitake mushrooms grow well in hardwood dowels. Other common substrates include coffee grounds, coconut coir, and sawdust. The substrate needs to be properly prepared by adding water, additional nutrition, and sterilisation or pasteurisation. Once the substrate is fully colonised by mycelium, it is ready for mushrooms to fruit.
| Characteristics | Values |
|---|---|
| Common substrates | Straw, coffee grounds, hardwood pellets, coco coir, vermiculite, manure, cardboard, wood chips, sawdust |
| Preparation methods | Pasteurisation, sterilisation, boiling water, fermentation, oven method |
| Additional supplements | Gypsum, bran, soybean hulls, millet, rice bran, wheat bran, oat bran, corn stalks |
| Ideal characteristics | Moist, nutritious, well-drained, properly hydrated, pasteurised/sterilised, contamination-resistant |
| Species-specific substrates | Oyster mushrooms: pasteurised straw, coconut coir; Common button mushrooms: composted manure; Chanterelles, Morels: specialised organic material mixes |
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What You'll Learn
Pasteurising straw
Straw is an inexpensive and effective substrate choice for growing mushrooms. Cereal straws such as oat or wheat straw are used as a base, or substrate, upon which mycelium grows. Mycelium is a thread-like collection of cells that represent the vegetative growth of a fungus.
There are various methods to pasteurise straw. The most common approach is to use hot water pasteurisation. This method can be done by placing the straw in a heat-resistant bag and filling it with boiling water. Allow the straw to sit for up to 8 hours or until completely cooled. Once cooled, drain the water.
Another method is cold water pasteurisation. This involves submerging straw in non-chlorinated water for around a week. During this time, anaerobic microorganisms, bacteria that survive without oxygen, multiply and start to break down the substrate.
Cold water pasteurisation can also be done using a lime bath. This involves soaking the straw in a bath of cold water that has been treated with hydrated lime. The lime will rapidly increase the pH of the water, causing mould spores, bacteria, and other contaminants in the straw to be killed off.
Alternatively, you can pasteurise straw using steam, or certain chemicals.
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Using coffee grounds
Coffee grounds are a great, eco-friendly way to grow mushrooms at home. Not only are they free and abundant, but they also come pre-pasteurised, saving you time and effort.
To get started, collect fresh coffee grounds from your local cafe. Espresso grounds are best, as filter or cafetière coffee is often too wet. You'll want to use the grounds within 24 hours of brewing to avoid mould.
Mix the coffee grounds with straw or sawdust. This will prevent the substrate from becoming too dense and compact, allowing for better air exchange. The general rule of thumb is that your mixture should be around 70% coffee grounds, 20% straw or sawdust, and 10% mushroom spawn. Weigh each ingredient on a kitchen scale to get accurate measurements.
Before mixing, pasteurise the straw by immersing it in boiled water at 170 degrees Celsius for one hour and fifteen minutes. Then, dump the straw into a strainer and a salad spinner to remove excess water. Using sanitised utensils or gloved hands, break up any clumps in the coffee grounds and straw. Add your mushroom spawn and break up any clumps.
Once your mixture is ready, place it into a clear plastic bag. Fill the bag halfway, as you may need to use more than one bag depending on the quantity of your mixture. Seal the bag tightly with a twist tie or elastic band, ensuring no air is trapped inside. Poke two to three small holes in the bottom of the bag.
Finally, place the bag in a warm (18-24°C) and dark place. Check on your mushroom substrate every few days. After two to three weeks, your bag should be fully colonised and bright white, ready for the next steps of mushroom cultivation.
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Mixing coco coir and vermiculite
To mix coco coir and vermiculite, start by adding 16 cups of water to a large pot and bringing it to a boil. Aim for a temperature of 74°C (165°F) or 65°C for pasteurisation. While waiting for the water to boil, place one standard brick of dried coco coir (around 1.4-1.5 lbs or 650 grams) and 8 cups of vermiculite into a bucket. You can also add a cup of gypsum to create CVG.
Once the water reaches the desired temperature, carefully pour it into the bucket and close the lid. Use a strong spoon or similar utensil to stir the mixture until the vermiculite is evenly distributed. Allow the mixture to cool to room temperature before using it as a substrate for mushroom growth.
After mixing and cooling, the coco coir vermiculite substrate is ready for inoculation. This involves adding mushroom spawn to the substrate. It is recommended to use a minimum of 20% spawn rate for wet coco coir vermiculite substrate, and a 50% spawn rate for plain coco coir substrate to speed up colonisation. Ensure that the spawn is mixed evenly throughout the substrate to avoid slower colonisation and increased chances of contamination.
Once inoculated, the substrate should be incubated in a warm, dark area at a temperature of 65-77°F (18-25°C). During incubation, the mushroom mycelium will spread from the grain spawn and grow through the substrate, feeding on the organic material.
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Preparing hardwood sawdust
Mixing the Substrate
Firstly, you will need to gather your materials. Hardwood sawdust is commonly used in the industry and is often a waste product of the lumber industry, so it may be easy and cheap to obtain. Commonly used hardwoods include oak, maple, beech, hickory, and teakwood. If you cannot source hardwood sawdust, you can use hardwood pellets, which are readily available and inexpensive. However, you will need to soak them in water before breaking them up into fine sawdust.
Next, combine your hardwood sawdust with supplements. A typical ratio is 5 parts sawdust to 1 part bran, such as wheat or oat bran. This supplement provides extra nutrients for the mycelium. You can also mix hardwood sawdust with soy hulls at different ratios to create a high-yield substrate, especially for growing oysters.
After mixing the dry ingredients, you will need to adjust the moisture content. The mixture should be moist but not dripping; around 60-65% moisture content is ideal. For supplemented sawdust fruiting blocks, mix in an appropriate amount of water before sterilisation.
Packing and Sterilisation
Once your substrate is mixed, fill your bags or containers, leaving enough space for mushroom growth. Ensure the mix is evenly distributed without being overly compacted, as this could hinder mycelial growth. Fold over the tops of the bags to allow gases to escape when heated.
To sterilise the substrate, you can use a pressure cooker or autoclave. Place the bags or containers inside and sterilise at 15 psi for 90 minutes to kill any unwanted bacteria or fungi. Alternatively, you can use an autoclave at 118-120°C and 15 psi pressure for 35 minutes. After sterilisation, allow the substrate to cool to room temperature in a clean area to prevent contamination.
Inoculation and Incubation
Inoculation involves introducing mushroom spawn into the substrate. You can purchase mushroom spawn online or from a local mushroom farmer. Sawdust spawn is best for outdoor use and is suitable for inoculating large quantities of logs or mushroom growing beds. Grain spawn is also an option and has more nutrients than sawdust spawn, allowing for even distribution throughout the sawdust.
Store the inoculated substrate in a dark, clean space with a stable temperature suitable for your mushroom species. Maintain a stable environment, avoiding temperature fluctuations and ensuring the area remains clean to prevent contamination. The mycelium will colonise the sawdust, appearing as white, thread-like structures. This process typically takes 2-4 weeks, depending on the mushroom species and environmental conditions.
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Sterilising manure
The process of sterilisation involves heating the substrate to a temperature above 120°C under pressure to kill any living or dormant contaminants. This step is crucial to giving your mushrooms a competitive advantage in the race to colonise the substrate. Sterilisation aims to kill all bacteria and pathogens, ensuring that your mushrooms have the best chance to grow and thrive.
To sterilise manure, you will need to mix it with other materials and water. A common recipe calls for two parts manure and one part coco coir, which is made from ground-up coconut husks and shells. Water is then added to reach field capacity, which means the substrate is moist but does not have excess water pooling at the bottom.
After mixing and hydrating the substrate, it needs to be sterilised. This can be done using a pressure cooker or an autoclave, which can reach the required temperature and pressure for effective sterilisation. The substrate should be placed in a heat-resistant bag or container and heated according to the equipment's instructions. It is important to follow safety precautions when working with high temperatures and pressure.
By properly sterilising manure-based substrates, you can create an optimal environment for mushroom growth, reducing the risk of contamination and giving your mushrooms the best chance to flourish.
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Frequently asked questions
Some common materials used for mushroom substrates include straw, hardwood sawdust, coconut coir, vermiculite, manure, coffee grounds, and cardboard.
To prepare straw for use as a mushroom substrate, you'll need to pasteurise it by submerging it in boiling water and allowing it to cool. Once cooled, drain the water and the straw is ready to be inoculated with mushroom spawn.
Coconut coir is a fibrous material made from ground-up coconut husks and shells, available at most garden stores. Vermiculite is a mineral that helps retain moisture and can be found at garden centres. To mix these two materials, place them in a clean 5-gallon bucket, pour in boiling water, seal the bucket, and allow it to cool before inoculating.
