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 unfermented 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 90° F., and not below 70°. The most favorable temperature, according to some, other conditions being congenial, ranges from 80° to 85° F., while many prefer to spawn at 70° to 75°. 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.
[WHAT SPAWN IS.]
The spawn of the mushroom is the popular word used in speaking of the mycelium of the mushroom. The term is commonly used in a commercial sense of material in which the mycelium is growing. This material is horse manure, or a mixture of one or two kinds of manure with some soil, and with the threads of the mycelium growing in it. The mycelium, as is well known, is the growing or vegetative part of the mushroom. Sometimes the word "fiber" is used by the mushroom growers in referring to the mycelium which appears in the spawn, or in the mushroom bed. The mycelium is that portion of the plant which, in the case of the wild varieties, grows in the soil, or in the leaf mold, in the tree trunk or other material from which the mushroom derives its food. The threads of mycelium, as we know, first originated from the spore of the mushroom. The spore germinates and produces delicate threads, which branch and increase by growth in extent, and form the mycelium. So the term spawn is rarely applied to the pure mycelium, but is applied to the substratum or material in which spawn is growing; that is, the substratum and mycelium together constitute the spawn.
Natural spawn or virgin spawn.—This is termed natural spawn because it occurs under natural conditions of environment. The original natural spawn was to be found in the fields. In the early history of mushroom culture the spawn from the pastures and meadows where mushrooms grew was one of the sources of the spawn used in planting. The earth containing the spawn underneath clumps of mushrooms was collected and used.
It occurs more abundantly, however, in piles of horse manure which have stood for some time in barn yards, or very often in stalls where the manure is allowed to accumulate, has been thoroughly tramped down and then has been left in this condition for some time. It occurs also in composts, hothouse beds, or wherever accumulations of horse manure are likely to occur, if other conditions are congenial. The origin of the natural spawn under these conditions of environment is probably accounted for in many cases by the presence of the spores which have been in the food eaten by the horse, have passed through the alimentary canal and are thus distributed through the dung.
The spores present in the food of the horse may be due to various conditions. Horses which go out to pasture are likely to take in with the food obtained in grazing the spores scattered around on the grass, and in the upper part of the sod, coming from mushrooms which grew in the field. In other cases, the spores may be present in the hay, having been carried by the wind from adjacent fields, if not from those which have grown in the meadow. In like manner they may be present in the oats which have been fed to the horse. In the case of stable-fed animals, the inoculation of the manure in this way may not always be certain or very free. But in the case of pasture-fed horses which are stalled at night probably the inoculation is very certain and very abundant, so that a large number of spores would be present in the manure from horses fed in this way.
The natural spawn also may originate from spores which are carried by the wind from the pasture or meadow mushrooms upon manure piles, or especially from spores which may lodge in the dust of the highways or street. Many of these spores would cling to the hoofs of the horses and at night, or at times of feeding, would be left with the manure in the stall. At other times horse droppings may be gathered from roads or streets where spores may be present in the dust. The piles of the droppings accumulated in this way, if left a sufficient time, may provide natural spawn by this accidental inoculation from the spores.