Substrate Types for Growing Mushrooms

What is Substrate?

Substrate is the growing media used for growing mushrooms in garden beds or containers. It provides the necessary nutrients, moisture, and support for the growth of mushrooms.

How to Choose the Right Substrate for Growing Mushrooms?

Different types of mushrooms require different substrates for optimal growth; for good yields and high-quality harvests, it is important to choose a compatible substrate. Use our reference chart, below, to identify a good substrate for your chosen mushroom strain(s). Use the chart below to find a suitable combination of mushroom strain, growing method, and substrate.

How to Prepare Substrate for Growing in Containers

Growers who are cultivating mushrooms in containers (indoors or outdoors) should prepare the substrate prior to inoculation. These preparatory steps reduce the risk of contamination by fungal or bacteria pathogens while still preserving beneficial microorganisms.

Begin with fresh substrate, which carries lower risk of contamination than substrate that has been allowed to age. Substrate may also be treated to reduce potential fungal or bacterial contaminants. Two common methods of substrate treatment include:

1. Cold water with hydrated lime: Mix 6 grams of hydrated lime for every 1 gallon of water. You may need to add more or less depending on the pH of your water. Measure the pH of the mixture and aim for 12.5 pH. Soak the substrate for at least 12 hours. Allow the substrate to drain until it is at the desired moisture content prior to inoculation. It should feel moist without dispelling large amounts of excess water.
2. Hot water: soak the substrate in hot water, maintaining a temperature between 145°F and 185°F for several hours to eliminate harmful pathogens while preserving beneficial microorganisms. If necessary, supplement with boiling water to achieve and sustain the desired temperature. Allow the substrate to cool to room temperature before inoculation. Adding mushroom spawn when substrate is too warm will likely kill off the mycelium.

How to Inoculate Substrate

Container Inoculation

Mushrooms can be grown in containers indoors or outdoors. Depending on the strain, mushrooms may fruit from either the side or the top of the container.

1. If side fruiting, use a container that already has side openings like a milk or bulb crate, or drill holes if the container does not already have them. Holes of ½" will allow mushrooms to fruit but minimizes moisture loss during colonization. If top fruiting, no holes are needed except the opening of the container.
2. To reduce the risk of contamination, sterilize the container.
3. Moisten your substrate. Ideally, you will achieve a 50% saturation of the substrate, or when the substrate weighs twice what it did when dry.
4. Break up and mix spawn, adding it at a rate of ½ bag to 1 full bag of spawn per 5 gallons of substrate. A higher ratio of spawn leads to faster and more reliable colonization and is recommended for beginner growers.
5. Add the substrate and spawn mixture to the desired container, mixing thoroughly or making alternating layers of substrate and spawn. 

Bed Inoculation

Some mushroom strains grow well in outdoor beds, between garden rows, or anywhere there is ample substrate. The volume that one bag of sawdust spawn can inoculate depends on bed depth and ratio of spawn to substrate, but in general, one bag of spawn can inoculate a 4’ x 4’ bed.

1. Prepare bed site by removing undesired plants or debris. 
2. Substrate can be hydrated to start, watered in between layers, or watered thoroughly at the end.
   • Wine Caps: begin with a layer of substrate 1” deep and crumble spawn on top, breaking up large pieces. Beginning with another 3–6" layer of substrate, continue alternating between spawn and substrate until out of spawn or have reached the desired bed depth. End with a final layer of substrate to protect the spawn.
   • Almond Agaricus: begin with 4–8" of substrate. Break the spawn up into 2” pieces and space the pieces around the bed 4–6" apart. Bury them a few inches below the surface, varying the depths slightly. 

Colonization

In the time between inoculation and fruiting, maintaining moisture levels is paramount. Allow the colonization process to happen in an area out of direct sunlight and monitor moisture levels.