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..
Horse manure is the material which is most generally used, though sometimes a small percentage of other manures, as sheep manure, is added. In the selection of the manure it is desirable to obtain that which is as fresh as possible, which has not passed through the stage of fermentation, and which contains some straw, usually as litter, but not too large a percentage of straw. Where there is a very large percentage of straw the manure is usually shaken out with a fork, and the coarser portion removed. If there is not too much of this coarse material the latter is often cured in a separate pile and used for the bottom of the beds, the finer portions of the manure, which have been separated, are used for the finishing and for the bulk of the bed.
View in mushroom house (L. S. Bigony). View on top of fourth bed, middle tier. Copyright.
Where manure is obtained on a large scale for the cultivation in houses or in caves, it is usually obtained by the carload from liveries in large cities. It is possible to contract for manure of certain livery stables so that it may be obtained in a practically fresh condition, and handled by the liverymen according to directions, which will keep it in the best possible condition for the purpose. In the cave culture of mushrooms the manure is usually taken directly into the caves, and cured in some portion of the cave. In the house cultivation of mushrooms there is usually a shed constructed with an opening on one or two sides, at the end of the house connected with the beds, where the manure may be cured. In curing it, it is placed in piles, the size of which will depend upon the amount of manure to be cured, and upon the method employed by the operator. The usual size, where considerable manure is used, is about three feet in depth by ten or twelve feet wide, and fifteen to twenty feet long. The manure is laid in these piles to heat, and is changed or turned whenever desirable to prevent the temperature from rising too high. The object of turning is to prevent the burning of the material, which results at high degrees of temperature in fermentation. It is usually turned when the temperature rises to about 1300 F. At each turning the outside portions are brought to the center of the pile. The process is continued until the manure is well fermented and the temperature does not rise above 100 to 120 degrees, and then it is ready for making into beds.
There are several methods used in the process of curing, and it does not seem necessary that any one method should be strictly adhered to. The most important things to be observed are to prevent the temperature from rising too high during the process of fermentation, to secure a thorough fermentation, and to prevent the materal from drying out, or burning, or becoming too wet. The way in which the material is piled influences the rapidity of fermentation, or the increase of temperature. Where the material is rather loosely piled it ferments more rapidly, and the temperature rises quickly. Watering the manure tends to increase the rapidity of fermentation and the elevation of the temperature. It is necessary, though, sometimes to water the material if the heat has reached such a point that it is becoming too dry, or if there is a tendency for it to burn. The material is then turned, and watered some, but care should be used not to make it too wet, since the spawn will not run in wet material.
In general we might speak of three different methods in the curing of the manure. First, the slow process of curing. According to this method, which is practiced by some, the time of fermentation may extend from four to five weeks. In this case the manure is piled in such a way that the temperature does not rise rapidly.
During the four or five weeks the manure is turned four or five times. The turning occurs when the temperature has arisen to such a point as to require it.
Another method, used by some, might be called a rapid process of curing. According to this, the time for curing the manure extends over a period of about a week, or five to ten days. The material is piled in such a way as to cause rapid fermentation and rapid rising of temperature, the material sometimes requiring to be turned every day or two, sometimes twice a day, in order to lower the temperature and prevent the material from burning or drying out. Between this rapid process of curing, and the slow process of curing, the practice may extend so that, according to the method of different operators, the period of curing extends from one week to a month or five weeks.
The third method of curing consists in putting the material at once into the beds before curing, and mixing in with the manure, as it is piaced in the bed, about one part of loam or garden soil to four or five parts of the fresh manure. The material is then left in this condition to cure without changing or turning, the temperature rising perhaps not above 1300 F. With some experience in determining the firmness with which the bed should be made to prevent a too high rise of temperature, this practice might prove to be successful, and would certainly save considerable labor and expense in the making of the beds. Mr. William Swayne of Kennett Square, Pa., in the winter of 1900-1901, made up a portion of one of his beds in this way, and no difference could be seen in the results of the crop, the crop from the beds made in this way being as good as that of the adjoining beds, and he intends the following year to make up all of his beds in the same way.
While in the cave culture of mushrooms the manure is usually fermented and used without the admixture of soil, usually in the house or cellar culture rich loam soil, or rotted sod, is mixed with the manure at the time of turning it, during the process of fermentation. At the time of the first turning, soil is mixed in, a layer of the manure being spread out on the ground, and then a sprinkling of soil over this. Then another layer of the manure is added with another sprinkling of soil, and so on as the new pile is built up. In the first turning of the manure, about one part of soil is used to eight or nine parts of manure. Then at the last turning another mixture of soil is added, so that there is about one-fifth part soil in the mixture. The soil aids somewhat in lowering the temperature, and also adds some to the bulk, so that more beds can be made up with the same amount of manure.
For growing mushrooms on a small scale, as in cellars or boxes, some prefer to select the horse droppings free from straw.