Mushrooms grow in organic material containing carbohydrates such as sugar, starch, cellulose or lignin, as well as the nitrogen required by all green plants. However, mushrooms cannot manufacture these products the way other plants do because they have no green color in their tissues. They develop their full root system, a network of fine white threads called mycelium, before any part of the plant appears above the soil. Fresh strawy horse manure is excellent for mushroom growing. It should be composted by turning it every four or five days, shaking thoroughly and watering well each time. Keep it moist, but not saturated. After three or four turnings, it should be a rich dark brown, with no odor. It can then be put in trays of any convenient size and allowed to “sweat out” heat to 140. After about a week, this should be ready for planting.
Many growers do not use horse manure as their special mushroom compost, but instead find it more practical to make compost using materials more readily available. Here is how to do it:
Mix together in a heap about 100 pounds of corn fodder or finely ground corn cobs and an equal amount of straw. Water and firm this well and let it stand a few days. Then mix in thoroughly 20 pounds each of leaf mold or peat moss, tankage, and either greensand or granite dust. Some well-rotted compost can be added to aid decomposition. About 30 pounds of sand completes the mixture. After a good watering, let it stand five or six days before turning. A second turning a week or so later should be enough before setting in the trays and planting. Plant the spawn as soon as the temperature of the beds reaches about 75o .