Fill your wooden tray or box with compost. Make your own compost or purchase ready-mixed manure and hay-based compost at garden or farm-supply stores.
Add 1 to 2 cups of dry flake mushroom spawn to your compost box. This culture taken from the mycelium, or body, of the mushroom will grow into button fungus. Mold the flake-compost mixture into mounds for the first 24 hours.
Spread the mushroom flake and compost piles until they are flat in the tray.
Lightly water the mushroom mix with a spray bottle.
Mix equal parts garden soil and peat together. Gently water the soil-peat compound until damp. Spread a 1-inch layer of the mix over the growing mushroom spawn.