Maintain temperatures of 70 degrees F to 80 degrees F. A high humidity can be maintained by using plastic tents to cover growing boxes.
Compost the growing medium: 40% hay or straw, 40% sawdust and 40% animal manure, preferably from horses or chickens.
As an optional step, you can bake the growing medium in an oven at 200 degrees F for 1 hour. This would kill any stray life in the compost. However, if the composting mixture has heated up well, this won't be necessary.
Find a heavy, waxed cardboard box of the appropriate size, or build a wooden box. The box should be 5 or 6 inches deep.
If you are going to grow large quantities, shelves or racks may be built to hold the growing boxes. When growing mushrooms, cover the entire rack or box with plastic.
Obtain edible mushroom spawn from a seed company, such as Gurney's Seeds of Yankton, South Dakota.
Fill the growing box with composted medium. Sprinkle in some spawn. Cover thinly with compost. Sprinkle gently with warm water, about a half cup per square foot. Place a plastic sheet over the box, allowing a little ventilation.
Water two or three times weekly. Make certain the soil does not dry out and is not spongy-wet. After three weeks, or after the first sign of life, add a half inch of loose compost. In four to six weeks, the first crop will be ready.
Harvest the mushrooms.
Sprinkle on an additional inch of composted mixture and repeat the growing process. After three or four crops, you will have to fix an entirely new boxful of potting compost, as the nutrients in the soil will be depleted. The old mixture will be good humus; spread it on your garden or potted plants.
To Dry Mushrooms:
Slice mushrooms thin and dry them on racks in your oven at 170 degrees F until brittle. One pound of dry mushrooms is equivalent to five to seven pounds of fresh mushrooms. Reconstitute by soaking in water, or add dry mushrooms directly to soup.