The horse droppings should be collected daily. If you have the facility to collect quantity enough to put in your desired bed all on one day so much the better. Keep it in a dry shed and turn the whole mass daily for eight to ten days. This is to prevent its violent heating. It is then in proper condition to make the bed. Choose a dry bottom always and where no drip will occur. Many writers say remove all straw from the manure. In the beds of the caves described they were not at all particular about this and there was considerable straw mixed with the droppings. Some modern writers advocate that at the last turning of the manure an equal amount of good fresh loam be added to the droppings, equal in weight but not in bulk. As mushrooms were grown for years without the addition of loam we do not believe it a positive essential. Its object is to prevent the bed heating too violently and we would recommend that loam to one-half the weight of the manure be added, and decomposed sod is better than soil from a garden because there would be less danger of dangerous fungi being introduced. Spread two inches of the compost on the floor, or whatever the bed is made on, and with a broad smooth mallet or brick pound down the material till it is quite firm and solid, then add two inches more and firm the same way, adding successive layers till the bed is of the desired thickness or depth. There is little difference of opinion as regards depth of bed, most authors say eight inches, some one foot. If much more than the latter depth too great a heat is likely to be generated. If less than eight inches the heat will be too weak and a small crop will be the result. I think ten inches of uniform depth is about right.
A thermometer should be sunk a few inches into the bed and it will be found that in two days the heat of the bed will rise to 100 degrees, perhaps more. When the heat is declining is the time to insert the spawn, and 90 degrees is generally agreed as the right temperature. A blunt stick or dibble is used and holes three inches deep are made at four or five inches apart over the surface of the bed. If the spawn is the English, which comes in compact bricks, then drop into each hole a piece of the spawn the size of a hen's egg. If the French spawn or material from an old bed, which may be much broken up, then fill the hole half full of the spawn and tamp it firm with a blunt stick, filling up the holes with the same material as the bed. Do nothing more till nine or ten days after spawning, when two inches of good virgin loam should be spread evenly over the bed and beaten down firmly until you have a smooth, even surface. This loam covering is to keep the manure at an equal temperature of heat and prevent dryness. The mycelium, or spawn, which should be vegetating before this covering of earth is put on, will soon spread and thickly occupy the covering of loam. The mushroom is really the fruit of the mycelium. If your bed is exposed to the light, as it would be beneath a greenhouse bench, then it is usual to cover the bed with two or three inches of hay to exclude the light so as to bleach or whiten the mushrooms. If exposed to light the top may be brown, which would render the mushrooms less attractive or salable. In totally dark situations the covering of hay would be quite unnecessary.
This completes all there is to say of the modus operandi to produce mushrooms, and as a cautious writer says, in six or seven weeks " expect" mushrooms. He does not say cut mushrooms, or you will have mushrooms, but " expect" them. And we can readily believe and know from experience that in many instances the expecting or anticipation is greater pleasure than the realization.
One important item remains., and that is watering. If the bed is not exposed to fire heat and the surrounding atmosphere is moderately moist, as it would be in cellars or caves, or even under a greenhouse bench, then seldom will any water be needed till you have cut the first crop of mushrooms, which may last three or four months. After that and after the manure becomes so dry that the mycelium ceases to vegetate, a watering at a temperature of 80 to 90 degrees will often produce a second crop equal to the first, and in some cases if on examination the bed is found very dry a watering to help the first crop may be necessary. We all know that after a warm August or September shower we expect to find a fine picking in our fields in the morning. It is not so generally known that mushrooms bear seeds or spores innumerable that when ripe and detached from the gills float away to other pastures.
Not many florists have the opportunity to study or read " Loudon's Encyclopaedia of Gardening." I am the lucky owner of this great gardening work and prize the volumes greatly, for my father is the author of the article on orchids for Mr. Loudon, at that time little known plants. In his exhaustive article on mushrooms he quotes a score of different authors and it appeals to me that a few extracts might be amusing or entertaining and maybe instructive. On light he says: "Abercrombie, Nichol and most gardeners and authors consider light as quite unnecessary for the production of mushrooms. It is very probable, however, that it contributes in some way to their perfection, since in their natural situation they enjoy a considerable portion of it. Our opinion is that it should not be entirely excluded from mushroom houses or beds." On gathering the crop he quotes Aber-crombie, who says: "When the bed is in full production and the season fine they can be gathered two or three times a week. Turn off the straw carefully and return it after each gathering. They should always be cut and never pulled, as by pulling many young ones may be destroyed. There are always a number of these forming or clustering about the roots of the old ones, which should not be disturbed." Wales says: "I have ever found the best adapted and most productive heat to be from 55 to 60 degrees, and the nearer the beds are kept to this heat the greater the success." This alludes to the temperature of the beds after fermentation has subsided.
Bed of Mushrooms.
In conclusion I will say that a good part of the literature of the mushroom is confined to the production of spawn, but that is a business entirely apart from the cultivation of the edible fungus and one that is left to the specialist. The English imported spawn is generally used, yet the remains of an old prolific bed are as good as any spawn that can be bought. The mycelium or spawn ceases to vegetate when the bed becomes dry and then rests and remains dormant as it does in the manufactured bricks, which are dried and if kept dry will last in good order for years.