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 artificial cultivation, the mushrooms usually formed are very near, or on, the surface of the bed. In the case of the meadow or pasture mushrooms, they are formed further below the surface. This is probably due to the fact that the conditions under which the mushrooms grow in cultivation are such that the surface of the bed is more moist, and is less subject to variations in the content of moisture, than is the surface of the ground in pastures. Although there may be abundant rains in the fields, the currents of air over the surface of the ground, at other times, quickly dries out the upper layers of the soil. But indoors the mycelium often runs to the surface of the bed, and there forms the numerous pinheads which are the beginnings of the mushrooms. The beds at this stage often present numerous clusters of the mycelium and these minute pinheads crowded very closely together. Hundreds or perhaps thousands of these minute beginnings of mushrooms occur within a small space. There are very few of these, however, that reach the point of the mature mushroom. Few only of the pinheads grow to form the button, and the others abort, or cease to grow. Others are torn out while the larger ones are being picked.
The time at which the mushrooms are picked varies within certain limits, with the different growers. Most cultivators, especially those who grow the mushrooms in houses, consider 60° F. the desirable temperature for the growth of mushrooms, that is, at a room temperature of 60° (while some recommend 570). The temperature of the beds themselves will be slightly above this. Under these conditions, that is, where the mushrooms are grown at a room temperature of about 60°, they open very quickly. It is necessary here to gather the mushrooms before they open, that is, before the veil on the under surface breaks to expose the gill surface. This practice is followed, of course, within certain limits. It is not possible in all cases, to pick every mushroom before the veil breaks. They are collected once a day usually. At the time of collection all are taken which are of suitable size. Many of them may not yet have opened. But in the case of some of the older or more rapidly growing ones, the veil may have broken, although they have not expanded very much.
Some follow the method of having the fireman, on his round at night, when he looks after the fires in the heating room, gather the mushrooms. He passes through all parts of the house and picks the mushrooms which are of suitable size. These are gathered by grasping a single mushroom by the cap, or where there is a cluster of mushrooms close together, several are taken in the hand. The plant is twisted slightly to free the stem from the soil, without tearing it up to any great extent. They are thrown in this condition into baskets. The collector then takes them to the packing room, and the following morning the plants are trimmed, that is, the part of the stems to which the earth is attached is cut away, the plants are weighed, put in baskets, and prepared for the markets. In other cases, the mushrooms are gathered early in the morning, in the same way, taken to the packing room, where the lower part of the stem is cut away, the plants are weighed, placed into the baskets and shipped to market.
In some of the caves, or abandoned mines, which I have visited, where the mushrooms are grown on a large scale, the practice in picking the mushrooms varies somewhat from that just described.
View in Packing Room (H. E. Hicks' Mushroom House. Kennett Square, Pa.) Copyright.
In the first place, the mushrooms are allowed to stand on the bed longer, before they are picked. They are rarely, if ever, picked before they open. Mushrooms may be quite large, but if they have not opened, they are not picked. Very frequently, the plant may open, but, the operator says, it is not open enough. It will grow more yet. The object of the grower, in this case, is to allow the mushrooms to grow as long as it is possible, before picking, for the larger the mushroom, the more water it will take from the bed, and the more it weighs. This may seem an unprofessional thing for a grower to do, and yet it must be remembered that a large water content of the mushroom is necessary. The mushrooms grown in these mines are very firm and solid, qualities which are desired, not only by the consumer, but are desirable for shipment. These mushrooms are much thicker through the center of the cap than those usually grown in houses at a room temperature of 6o° F. For this reason, the mushrooms in these caves spread out more, and the edges do not turn up so soon. Since the cap is so thick and firm at the center, it continues to grow and expand for some little time after having opened, without turning up on the edges, and without becoming black and unsightly underneath. These large and firm mushrooms are not only desirable for their shipping qualities, but also, if they are not too large, they are prized because they are of such a nice size for broiling.
It is quite likely that one of the important conditions in producing mushrooms of this character is the low temperature of the mine. The temperature here, in July and August, rises not higher than 580 F., that is, the room temperature of the mines; while in the winter it falls not lower than 520. The growth of mushrooms, under these conditions, may not be quite so rapid as in a house maintaining a room temperature of 60°. The operator may not be able to grow so many crops from the same area, during the same length of time; but the very fact that this low temperature condition retards the growth of the mushrooms is perhaps an important item in producing the firm and more marketable product, which can be allowed to grow longer before it is picked. It is possible, also, that another condition has something to do with the firmness and other desirable qualities of these mushrooms. It is, perhaps, to be found in the fact that natural spawn is largely used in planting the beds, so that the spawn is more vigorous than that which is ordinarily used in planting, which is several or many generations distant from the virgin condition.
The methods of picking in this mine differ, also, from those usually employed by growers of mushrooms. The mushrooms are pulled from the bed in the same way, but the operator carries with him two baskets and a knife. As fast as the mushrooms are pulled, and while they are still in hand, before the dirt can sift upon the other mushrooms, or fall in upon the gills of those which are open, the lower part of the stem is cut off. This stem end is then placed in one basket, while the mushrooms which have been trimmed are placed in another basket. In cutting off the stems, just enough is cut to remove the soil, so that the length of the stem of the mushroom varies. The mushrooms are then taken to the packing room in the cleanest possible condition, with no soil scattering therefrom or falling down among the gills, as occurs to a greater or lesser extent where the mushrooms are picked and thrown indiscriminately into baskets.