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..
Where only the floor of the house is used, a middle bed and two side beds are sometimes formed in the same manner as described in the construction of the house for the tiers of beds, with an alley on either side of the large center bed, giving access to all. In some cases the entire surface of the bottom is covered with material, but divided into sections of large beds by framework of boards, but with no alleys between. Access to these beds is obtained by placing planks on the top of the boards which make the frame, thus forming walks directly over portions of the bed. In some cases ridge beds, as described for cave cultivation, are made on the floor of these houses. The beds are filled in the same way as described for the cave culture of mushrooms, but usually, in the beds made in houses built for the purpose of growing mushrooms, a percentage of soil is mixed in with the manure, the soil being usually mixed in at the time of turning the manure during the process of fermentation.
Garden soil or rich loam is added, say at the first time the manure is turned while it is fermenting. Then, some time later during the process of fermenting, another admixture of soil is added. The total amount of soil added is usually equal to about one-fifth of the bulk of the manure.
As this material, formed of the manure with an admixture of soil, is placed in the beds it is distributed much in the same manner as described for the making of flat beds in caves or tunnels. Usually, however, if there is coarse material which was separated from the manure at the first sorting, this without any mixture of soil is placed in the bottom of the bed, and then the manure and soil is used for the bulk of the bed above. This coarser material, however, is not always at hand, and in such cases the beds are built up from the bottom with the mixture of manure and soil. The depth of the material in the beds in these houses varies according to the experience of the operator. Some make the beds about eighteen inches in depth, while others do not make the beds more than eight or ten or twelve inches in depth. Where there are tiers of beds, that is, one bed above the other, very often the lowest bed, the one which rests directly upon the ground, is made deeper than the others.
While it is the general custom to use material consisting of an admixture of manure and soil in the proportions described, this custom is not always followed. In the case of the beds which are made up in the summer for the fall and early winter crop, soil, being easily obtained at that season of the year, is mixed with the manure. Some growers, however, in making the beds in midwinter for the spring crop, do not use any soil since it is more difficult to obtain it at that season. In such cases the beds are made up of manure alone. The experience in some cases shows that the crop resulting from this method is equally as good as that grown where soil has been added. In the experience of some other growers a bin of soil is collected during the summer or autumn which can be used in the winter for mixing in with the manure and making the beds for the spring crop. Where sod is used this is collected in pastures or fence rows in June, piled, and allowed to rot during the summer.
In distributing the material in the beds, the methods of packing it vary according to the wishes or experience of the grower. It is often recommended to pack the material very firmly. The feeling that this must be packed very firmly has led to the disuse of beds in tiers by some, because it is rather difficult to pack the material down very firmly where one bed lies so closely above another. Where the practice is followed of packing the material very firmly in the bed, some instrument in the form of a maul is used to tamp it down. Where there are tiers of beds an instrument of this kind cannot well be used. Here a brick or a similar heavy and small instrument is used in the hand, and the bed is thus pounded down firmly. This is a tedious and laborious operation. Many growers do not regard it as essential that the beds should be very firmly packed. In such cases the material is distributed on the beds and the successive layers are tamped down as firmly as can well be done with the back of a fork or an ordinary potato digger, which can be wielded with the two hands in between the beds. In the experience of these growers the results seem to be just as good as where the beds are more firmly packed down.
It is the practice in some cases where the bed lies against the side of the house to build up the material of the bed at the rear, that is, at the side of the house, much deeper than at the front, so that the depth of the bed at the back may be eighteen to twenty inches or two feet, while the front is eight to ten or twelve inches. This provides a slightly increased surface because of the obliquity of the upper surface of the bed, but it consumes probably a greater amount of material. It probably is not advantageous where the operations are carried on on a large scale, where abundant room is available, where the material for making the beds is expensive, and it is desirable to obtain from the material all that can be drawn in a single crop. The same practice is sometimes recommended and followed in the case of the beds made in cellars.
In the making of beds with fresh material, that is, with unfer-mented manure, as was done by Mr. William Swayne of Kennett Square, Pa., one season, the coarser material is put in the bottom of the bed, and then as the manure is distributed in the bed the soil is sprinkled on also, so that finally when the bed is completed the proportions of soil and manure are the same as when it is mixed in at the time of fermentation. In making the beds in this way, should any one be led to attempt it, it would be necessary to guard against a too high temperature in the fermentation of this fresh material; the temperature should not run above 130 degrees. It would also require a longer time from the making of the bed to planting the spawn than in the case of those beds where the manure is fermented and cured before being made up. Probably the total amount of time from the beginning to the completion of the preparation of the bed for spawning would not be greater, if it would be so great.
The beds all having been made, they are left until they are in a suitable condition for spawning. The determination of this point, that is, the point when the beds are ready for planting the spawn, seems to be one of the most important and critical features of the business. The material must be of a suitable temperature, preferably not above 900 F., and not below 700. The most favorable temperature, according to some, other conditions being congenial, ranges from 8o° to 850 F., while many prefer to spawn at 700 to 750. Many of the very successful growers, however, do not lay so much stress upon the temperature of the bed for the time of spawning as they do upon the ripeness, or the cured condition, of the material in the bed. This is a matter which it is very difficult to describe to one not familiar with the subject, and it is one which it is very difficult to properly appreciate unless one has learned it by experience. Some judge more by the odor, or the "smell," as they say, of the manure. It must have lost the fresh manure "smell," or the "sour smell," and possess, as they say, a "sweet smell." Sometimes the odor is something like that of manure when spawn has partly run through it. It sometimes has a sweetish smell, or a smell suggestive of mushrooms even when no spawn has run through it.
Another important condition of the material is its state of dryness or moisture. It must not be too dry or the spawn will not run. In such cases there is not a sufficient amount of moisture to provide the water necessary for the growth of the mycelium. On the other hand, it must not be too wet, especially at the time of spawning and for a few weeks after. Some test the material for moisture in this way. Take a handful of the material and squeeze it. If on releasing the hold it falls to pieces, it is too dry. By squeezing a handful near the ear, if there is an indication of running water, even though no water may be expressed from the material, it is too wet. If on pressure of the material there is not that sense of the movement of water in it on holding it to the ear, and if on releasing the pressure of the hand the material remains in the form into which it has been squeezed, or expands slightly, it is considered to be in a proper condition so far as moisture is concerned for planting the spawn.