How to Grow Mushrooms on Already Pasteurized Manure

Choose your spawn. Spawn is similar to the seeds for growing a plant. Spawn is grown in special laboratories keeping it pure, as airborne fungal spores can contaminate it. Make your choice dependant on what you are looking for in the finished mushroom and based on growing substrate. Shitake mushrooms grow on wood substrate and are thus unsuitable for manure substrate.

Inoculate the horse manure. Inject the spawn into the manure substrate, giving it time to spread. Signs of successful inoculation are thread-like mycelium that is blueish to white and a rise in the substrate temperature. Growing mycelium raises substrate temperatures to between 80 and 85 degrees Fahrenheit.

Allow 14 to 21 days for spawning to be completed, maintaining substrate temperatures between 74 and 85 F. Cooler temperatures arrest or slow growth, while warmer may kill the mycelium.

Apply casing to the substrate. This is a mulchlike layer consisting of any moisture-holding organic material, such as peat moss and ground limestone, clay-loam soil or spent compost. As the mycelium fuses into thick strings called rhizmorphs, the casing provides a place for them to go while retaining moisture. Hold the casing temperature at 75 F for up to five days with at least 85 percent relative humidity.

Water the casing layer intermittently, keeping moisture high until pin formation.

Lower the casing temperature by 2 degrees a day after five days until initials begin forming. Initials, or pins, are the beginning mushroom sprouts. From casing to mature mushrooms takes between 18 and 21 days.

Introducing fresh air into the growing area lowers the air's carbon dioxide content .08 percent. Airing too early causes the mycelium to arrest forming the pins, or may cause it to grow them below the casing, resulting in dirty mushrooms when they finally push through. Too little water may also cause this.