Best results are obtained by growing under cover, say in a shed, cellar, garage, etc., where semi-darkness is normal. Hot water pipes to supply a moist heat are ideal but the main points are perfect ventilation, even temperature of 50 — 6o° F. and high. Darkness is obviously not essential, otherwise mushrooms would never flourish in fields, but it does assist in keeping an even temperature. Mushrooms can be grown in the open — but it is asking for rather a lot of work giving inadequate result. Mushrooms grow on prepared stable manure beds and these beds can only be used for one growth, not a second supply. The mushrooms develop from fungus growths known as mycelia, popularly called spawn, and supplied in prepared slabs. The manure must be absolutely free from impurities and it must be fresh straw manure, stacked not less than 4 ft. high, to ferment, and any dry patches kept moist by sprinkling. After a fortnight thoroughly turn the heap, noting temperature, which should be 150 degrees F. Give another forking a week later, and 4 days later, when it should not smell acrid, be brown and warm, the heap should be lifted by fork into the shed, turning it all in the moving. A temperature of 70 degrees F. is right for spawning. If the bed remains too hot, pierce into the body here and there to reduce heat; a dibber thrust in to about 1 ft. will do.
For beginners, a flat growing bed is probably better than a conical one. Make it 1 ft. high all over, as long as convenient, and 3 ft. 6 in. across. Keep a thermometer handy and take tests. When the temperature drops to 70 degrees F. put in the spawn (mycelium). Break pieces, often marked but if not, the size of a plum, off the brick, and at 9 in. intervals in criss-cross fashion thrust a piece into prepared holes about 2 in. deep and then fill up, pressing the manure firmly round the spawn in closing hole, to exclude air. After a fortnight the whole bed must be cased with a couple of inches of sterilised soil, on top and all sides, pressed down firmly everywhere. The soil must be friable and covered with clean straw or hay about 1 ft. thick. The spawn should now do the rest, but draughts must be excluded, temperature kept even, light dim, and in a couple of months the cropping can start. If during the maturing period a white, threadyappears on the heap take a brush and remove it.
Ridge Bed. Make manure into a 2 ft. 6 in. cone with a 3 ft. 6 in. base (or 4 ft. with 6 ft. base if space allows), add soil layer of same thickness and at same time as for the flat bed, but also cover the lot with straw to about 3 in. all over, to hold soil in, a proceeding unnecessary with a flat bed. Some find it more convenient for attention to put flat beds round the sides of the shed and conicals in the centre. Those unable to obtain stable manure have various alternatives, e.g. the use of wheat straw decomposed by a proprietary compound, or proprietary composts which only need moistening prior to spawning.
Mushrooms can certainly be grown in the open, and in lawns or pasture land, but, as stated, for an amateur the preparation necessary and the uncertainty of even fair results make it hardly worth the time and labour. If, however, mushrooms appear spontaneously on such land, a few pieces of spawn pocketed below the surface will sometimes develop a satisfactory crop.