A substrate is anything which the mushroom can digest and use for energy while it grows. There are two very different kinds of substrates which are used in mushroom cultivation: highly nutritious spawn substrates and mildly nutritious bulk substrates.
Common spawn substrates
- Rye berries is also known as rye grain but should not be mistaken for rye grass seed. Rye berries are the most commonly used grain substrate due to their relative low price and the ease of which they can be broken apart after full colonization. Rye seed can be found at most organic food stores. Take care to avoid fungicide treated rye seed.
- Brown Rice, most popular for its use in the BRF Cakes of the PF Tek, is most commonly used in its powdered form. Brown rice flour (aka BRF) can be found at most grocery stores. PF Tek is the most famous growing method using brown rice flour but others use it in various mixes.
- Wild Bird Seed is commonly abbreviated "WBS" and is often a mixture of several different types of seeds that are intended to be used in a bird feeder. It can be used as either a loose grain or as a cake substrate. When it is dry, it can be powdered to create a flour commonly abbreviated as "WBSF".
- Popcorn Seed is a common substrate which can be used in its uncooked form in a fashion similar to rye berries.
Common bulk substrates
- Coconut coir is the shredded fiber of coconut husks. It holds many times its weight in water but does not decompose for years. It is PH neutral and inexpensive. Hydroponics stores and hardware stores sell it in compressed bales & pet stores sell it in dried bricks.
- Worm castings