This section is from the book "Studies of American Fungi: Mushrooms, Edible, Poisonous, Etc.", by George Francis Atkinson. Also available from Amazon: Studies of American Fungi: Mushrooms, Edible, Poisonous, Etc..
Obtain fresh stable horse manure mixed with straw used in bedding the animals. Shake it out, separating the coarse material from the droppings. Put the droppings in a pile two to three feet deep. Pack down firmly. When the heat rises to near 1300 F., turn and shake it out, making a new pile. Make the new pile by layers of manure and loam soil, or rotted sod, one part of soil to eight or nine parts of manure. Turn again when the heat rises to near 130o F., and add the same amount of soil. When the temperature is about 100° F., the material is ready for the beds.
Make the beds as described under the paragraph on pages 250-253, or use boxes. Place the coarse litter in the bottom three to four inches deep. On this place three to four inches of the cured material, pack it down, and continue adding material until the bed is ten to fifteen inches deep. Allow the beds to stand, covering them with straw or excelsior if the air in the cellar or shed is such as to dry out the surface.
Test the moisture content according to directions on page 255.
Watch the temperature. Do not let it rise above 1300 F. When it is down to 900 F. or 700 F., if the manure has a "sweetish" or "mushroomy " smell it is ready to spawn.
Spawn according to directions on page 263.
Soil according to directions on page 266; cover bed with straw or excelsior.
Use horse droppings freed from the coarser material. Proceed as in first method.
Use horse droppings freed from coarser material. Pile and pack firmly'. Do not let temperature rise above 130o F. When it has cooled to 100° F., make up the beds, at the same time mixing in an equal quantity of rich loam or rotted sod. Spawn in a day or two.
In beginning, practice on a small scale and study the conditions thoroughly, as well as the directions given in this chapter.