Mushroom Growing - A Practical Manual

INTRODUCTION

IN THIS BOOK I have concentrated upon the most usual method of commercial culture of mushrooms, of which I happen to have experience, and have only briefly described other commercial methods used in this country, details of which can be obtained from books specialising in them. The general principles of culture, however, are identical in all cases.

I would warn readers, however, to take mushroom books with a pinch of salt. Reasons and details of culture are so often given as matters of fact and certainty when, in the light of further experience, they are found to be matters of opinion, tradition or experience under certain conditions only. Casing soil must be a medium loam . . . etc., when we all know the man round the corner who uses ashes and gets wonderful crops. Until we know more of the biology of the mushroom it is unwise to lay down too rigid a set of conditions to any intending grower. It works on our nursery—we get good crops should be the motto of all authors on this subject. I have tried to make it mine. The only way to obtain a balanced view is to discuss a subject with as many other growers as possible, using books for the groundwork. But as long as a book is only an expression of opinion, because the facts are uncertain, then just so long must it be used only as an opinion and temporary foundation. If mushroom growing could be learnt by book alone, mushrooms would not be sold in the shops at 10s. per pound.

CHAPTER I

FIRST PRINCIPLES

"HOW do you grow mushrooms?" This question has been asked of mushroom growers for hundreds of years, and is still asked to-day. Secrecy has always surrounded the cultivation of this most mysterious crop—the very speed with which the fruits appear above the soil has a magical quality when compared with the slow period of growth and ripening of other fruits and vegetables.

Nearly all other food plants are green. They build up their leaves, stems and fruits from raw materials present in the soil and air, and use sunlight as a power supply to convert these raw materials to the complicated chemicals making up their bodies, which we use as food; unlimited sunlight can do damage to the plant; its power is controlled and tempered down by the green colouring matter present in the leaves of the plant. Mushrooms belong to the group of plants called fungi. They have no green matter, and have no need of it, for they are independent of sunlight. They make use of the half-broken down chemicals from decaying plants and animals and bacteria, broken down but not far enough to need the sun’s energy to build them up again into mushroom tissue. They can thus grow in the dark. Chemicals can only be changed slightly without the help of sun energy and so the mushroom needs to feed on certain special sorts of chemical not very far distant from those within its own body. It also needs rather exact conditions of temperature, water supply and so on, to help in the conversion of these chemicals, and it is these fussy requirements that make the mushroom so much more difficult to grow than other vegetables, and so different in its cultivation. A man who can grow turnips well, has no trouble in growing marigolds or wheat—he will at any rate get some crop from them. But when it comes to mushrooms, it is quite a different matter. Not that a good gardener, trained to be accurate and observant, cannot grow them as well, so long as he realises that they are very different from his other crops. This first chapter therefore will follow the mushroom throughout its life, give a general picture of how it works, and show briefly how the grower provides for the fussy tastes of his mushrooms.

FIG. 1. Stages of mushroom growth. A.—Mycelium, natural size. B.—The same, much enlarged. C and D.—Formation of buttons. E.—Section through a button. F and G.—The cup stage. H.—Section through a ripe gill to show spores.

The seed of a mushroom is called a spore; spores are found as a fine dust on the dark brown gills of old mushrooms. In the country they are responsible for the spread of the mushroom from field to field, and many people believe that the horse helps this spread by eating the spores mixed with its grass, and passing them out later in another part of the field unharmed and embedded in what soon turns into first-class compost. This may be one reason why horses seem to be connected with mushroom fields, though there have been other suggestions. In a suitable field, and with warm moist conditions, the spore germinates, and from it grow out greyish threads which look like cobweb strands. These threads are to be found under the turf in mushroom fields, and they are not merely the roots of the mushroom, but the whole body of the fungus for the greater part of the year. The scientific name for the threads is mycelium. The threads spread out and nourish themselves with decaying grass roots and stems, together with nitrogen-containing chemicals. These nitrogen supplies are formed from animal droppings and urine lying on the turf, and washed through by rain. In autumn, when warm wet rains fall on to the turf, and night temperatures are low, the mycelium becomes very matted, and at places the mat thickens and bulges into the shape of a small mushroom. The tiny pip by the intertwining of a great many strands, enlarges within a few days and appears above ground. The stalk is the last part to enlarge and this raises the cap of the mushroom above the ground. Within this cap lie the pink gills—folds of tissue which bud off millions of minute spores; the gills are sealed off from the outer world by the veil of the mushroom which stretches from the edge of the cap to the stalk. Presently the cap expands still further and changes from a round to a flat shape, the gills become stretched out, the veil breaks with the strain, and the spores are blown away to new areas or on to the grass where many are certainly eaten by, and perhaps survive a passage through, the digestive system of grass-eating animals. It is thus clear that the mycelium (or spawn, as the grower calls it) represents the leaves and stem and roots of an ordinary flowering plant. The mushroom itself is rather like the flower of a plant, for it bears the spores or seed.*

How then does the grower imitate natural conditions on his mushroom farm? The building up from spore to cropping stage takes a long time, and only in the spawn-breeding laboratories are spores used at all, though even there tissue culture is more usual. The grower faced with coal and wage bills does not bother to start with the spore. Just as the nurseryman grows Cox’s Orange apples not from seed but from buddings or graftings, so does the mushroom grower take small pieces of ready-grown mycelium, or spawn, and so get his crop more quickly and easily. In this, he has not imitated nature, but in the rest of the culture, he does follow closely the conditions found in the field. The wet warm autumn is imitated by having heated sheds for the crop, with frequent damping of the beds. Sudden cold, which brings the wild crop to a close, is carefully avoided by heat insulation of the sheds. The grower does not use dead turf and animal droppings, but he does imitate that material by rotting down stable manure—horse droppings and straw or even these days pure straw and artificial nitrogen manures, the resulting compost being a rich mixture of cellulose, lignins and complicated nitrogen compounds which resembles the natural material. Compost is not only richer than the mixture in which wild mushrooms grow, but it is provided in a much thicker layer than would be found in the field. On top of the compost is placed an inch or so of casing soil, which probably performs the same function as the soil and turf in the meadow—that of supporting the mushroom, preventing the compost drying out and, by evaporation, providing a cool top to the bed which may have something to do with the production of fruiting bodies. True, nature does not check disease or fly attacks on her crops, as does the grower with his elaborate sprays, fumigations and hygiene; but then nature does not have to make a living from her maggoty or mildewed mushrooms. Control of disease is one of the major worries of the grower, and much skill and expense is necessary if large crops are regularly grown.

FIG. 2. Natural and Artificial Growing Compared.

Three common species of mushroom occur in this country. Psalliota campestris, the Common Edible Mushroom is the one usually picked wild; many strains or varieties are to be found. Psalliota arvensis is the Horse Mushroom. It is larger than the Common Edible, and reaches 4-6 inches in diameter; it can be distinguished by the fact that it does not go brown