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..
In the cave culture of mushrooms the beds are usually made from manure alone, there being no addition of soil. This is perhaps partly due to the expense of getting the soil in and out from the caves as well as to the low temperature prevailing there. It is believed by many that the results are equally as good in beds from the manure alone as in those which contain an admixture of soil. The method of making the beds in the Akron cave, or "tunnel," is as follows : The manure, immediately after it has passed through the process of fermentation and curing in the pile, is carted to the district in the mine where the beds are to be made and is dumped in a long windrow on the ground. The length of the windrow depends of course upon the amount of material which is ready, as well as upon the amount necessary for making up the beds for that distance. Two hemlock boards, sixteen feet long and ten inches wide, and two, four feet long and the same width, are then hastily nailed into the form of a rectangular frame. This is placed upon the rock bottom at one end of the row of material, perpendicular to it usually.
The workmen then, with forks, distribute the material in this frame. If there is coarser material which has been separated from the finer material, this is placed in the bottom of the bed and the finer material is then filled on top. A layer of material is distributed over the bottom and then tamped down by striking with the back of the fork, as shown in Fig. 232. In this figure the material is shown to be off at one end of the bed. This was in a section of the mine where it was not convenient to follow the beds in the direction of the pile of manure, so that the material is distributed on from the end of the bed instead of from the side, as is the usual method. After several inches have been distributed in this way and tamped down with the back of the fork, the operator tramps over the material with his feet and presses it down more firmly. Another layer of material is distributed over this, and tamped and tramped down in a similar manner. The operation is repeated until the depth of the manure after tramping down is about seven inches. It is then left for the completion of the curing process and for the lowering of the temperature to the desired point. Usually, after making the bed in this way, there is a rise in the temperature for several days, gradually lowering until finally it reaches the point favorable for planting the spawn.
View in Akron " tunnel," N. V. Mushroom Co. Making up the beds. Copyright.
Where the beds are made successively, one after another, following the windrow of manure, the material used for the first bed removes from the windrow a sufficient amount to make room for the second bed, and in like manner room for the successive beds is provided for as the material is taken for each one, so that the frames are put together and the beds are formed rapidly and easily.
In the making of the ridge beds in caves there are two methods which might be spoken of. One method is the well known one practiced in certain of the caves near Paris, where the material is taken by workmen in large baskets and distributed in rows. The ridge is gradually formed into shape by walking astride of it, as additional material is emptied on from the baskets, the workmen packing and shaping the ridge by pressure from their limbs as they stand astride of the row. In this way the ridges are made as high or somewhat higher than their breadth at the base, and quite near together, so that there is just room in many cases to walk between the beds. In one cave in America, where the ridge system is used to some extent, the ridges are made with the aid of a board frame the length of the bed and the width of the base of the ridge. The long boards of this frame are slanting so that they are more or less the shape of the ridge, but not equal to its height. This frame is placed on the rock bottom, filled with manure and tramped on by the workmen. Then the frame is lifted on the ridge and more material is added and tramped on in like manner, until the bulk of the ridge bed is built up in this way and compressed into shape.