Guide to Growing Mushrooms
One of the most popular foods, mushrooms are different in character, shape, and method of cultivation from other vegetables. They are widely grown commercially, but mushrooms can easily be cultivated on a smaller scale by the home grower. Mushrooms are expensive in the shops all through the year, and it is much more economical to grow them yourself, as the initial outlay is quite small. A second point in favour of homegrown mushrooms is that mushrooms are at their best when freshly picked; they quickly lose their flavour and become tough and stale. The best guarantee that the mushrooms are fresh is to harvest them yourself just before cooking. A third point is that you can superintend the ingredients and making of the growing medium yourself, and so choose materials for thewhich will ensure the same rich flavour in your home-grown mushrooms that the wild field mushroom has. In the kitchen, mushrooms can be used whole or chopped, and eaten raw in salads or cooked by almost any method. Most of the work in growing mushrooms is connected with the preparation of the special compost in which they grow; after the compost has been prepared, very little is needed in the way of cultivation and care.
Botanically, mushrooms are the fruiting bodies of the fungus Agaricus bisporus. The entire growth above the ground is edible; it consists of a white, creamy or brownish cap on a brownish stalk. Mushrooms change shape slightly as they mature. Young mushrooms first appear as white pinheads on the surface of the mushroom bed; they develop short stalks as the buttons, or caps, grow larger. At this stage the caps are spherical in shape and the gills are covered with a membrane, or veil, which is connected to the stalk. As the mushroom matures, the stalk grows longer and the cap grows larger and begins to flatten out. The membrane tears as the cap expands, and exposes the brownish gills beneath.
The usual method of propagation is by spores, which are produced in the gills and correspond to the seeds of green plants. Because the brownish black several species of wild mushrooms which are highly poisonous, and very similar in appearance to those which are edible. Unless you are fully knowledgeable about mushrooms, and can identify them accurately, it is best not to pick wild mushrooms for eating.
Mushrooms are grown commercially in purpose-built mushroom houses and artificial caves, but the home grower should be able to find a suitable site, either indoors or out, for growing smaller crops of mushrooms. The main factors in growing mushrooms powdery spores are microscopic in size and difficult to germinate except under special conditions, mushrooms are normally grown from spawn. Spawn, or mycelium, is the germ tube produced by the spores; each appears as a long, thread-like white filament. The spawn absorbs food and moisture from the compost and eventually produces the fruiting bodies, or mushrooms, which are then cropped.
Cultivated mushrooms are closely related to the edible wild mushrooms (Agaricus campestris) found in summer and autumn in fields and meadows. A word of warning, however: there are successfully, besides suitable compost, are stable air temperature and moisture; you must select a site where these can be controlled. Indoors, you can use the floor of a cellar or shed; outdoors, they can be grown in greenhouses, cold frames or, in mild areas, in the open. Wherever they are grown, it is probably most convenient if you use boxes, other than beds, to contain the compost, remembering that boxes have the disadvantage of being wasteful of space.
If you are growing them in a shed or cellar, it must be clean, waterproof and dark. It is a good idea to disinfect old buildings before attempting to use them for mushroom growing, and dust the floor with lime as an additional precaution. It will be much easier to regulate the temperature inside a building if it is insulated; mushrooms will not grow if the temperature rises above 27°C (80°F) or falls below 7°C (45°F). There should also be some form of ventilation, so that the air can circulate freely. You can grow your mushrooms in wooden boxes or trays, with a depth of about 20 cm (8”) and any convenient size. You can also make up ridges directly on the floor, each about 45 cm (1-J’) deep, and with a base of 60 cm (2’), rounding the top of the ridge. Or you can use a flat bed about 20-25 cm (8-10”) deep, but make it convenient for picking.
You can grow mushrooms in your greenhouse from mid-autumn through to mid-spring, if it is heated; under the staging is the best place to grow them, putting the compost either in boxes or directly on the greenhouse floor. They can also be grown on the staging, in containers; you will have to shade the glass fairly heavily as mushrooms become brown when exposed to sunlight, or make some arrangement to cover the containers or bed so as to exclude the light to some extent.
Outdoors, mushrooms can be grown in frames which are fairly deep; you will need a depth of at least 45 cm (1-1/2’)s though 60 cm (2’) is better. This allows a depth of compost of between 30 and 45 cm (1 – 1-1/2’) and also gives reasonable conditions in which to keep the right temperature and humidity and allow the mushrooms room to grow. Lights will also be needed, and mats to shade the growing mushrooms. In very mild areas, mushrooms will grow outdoors on ridges from late winter through early summer and again from early autumn through late autumn. Make the ridges 60-75 cm (24-30”) wide and 45 cm (18”) high, and as long as is suitable. You can have them higher but not lower, since less good results will be obtained. You will need a good supply of straw and plastic sheeting in case of heavy, prolonged rain.
You can also grow mushrooms in a lawn or field. This is a chancy method, but can sometimes produce successful results. Simply lift a piece of turf in late summer and place the spawn beneath it. Theshould be moist, and the atmosphere warm and humid. A touch of frost will not damage outdoor grown mushrooms. Finally, it is possible nowadays to buy mushroom kits which take the backbreak out of mushroom cultivation. They consist of a bucket containing prepared compost, which has already been spawned; you simply add water to start the spawn growing, carry out a few other simple instructions and pick mushrooms a few weeks later.
As it is important to know the temperature of the compost during the various stages of making it, you should obtain a soil thermometer.
Mushrooms are usually grown on a compost made from strawy horse manure. Other materials can be used, such as pig or cow manure or any animal manure; wheat straw with fertilizer added has been tried and is much used commercially, also barley or bean straw, and bracken, again with the addition of nutrients. If you are making compost from horse manure, make sure it is fresh and has not been exposed to the weather for a long time. You should begin preparing the compost about a month before it is needed. Stack the manure in piles about 1.2 m (4’) high. This can be done outdoors in the summer; otherwise the stacking must be done in a shed or similar building to protect the manure from wet weather.
If it is at all dry, water the manure; it should be moist but not really wet. If it is almost pure dung, without much litter, add wheat straw in the proportions of 1 part straw to 10 of dung (by volume) and mix thoroughly. Leave the stack alone for about seven days, during which time it will begin to ferment; the temperature inside it should be in the region of 65°C (150°F). This will kill alland should destroy most fungal diseases. Once it has reached this temperature, you can turn it, putting the manure that was on the outside into the centre of the new heap, and breaking up all lumps as you proceed. Shake it at the same time to aerate it. Turn the stack another four or five times, at about four-day intervals, moistening the manure if it is at all dry. In about three to four weeks time, the compost should be brown, crumbly and moist, with the straw still recognisable but only just, and there should no longer be a smell of ammonia. It will now have a temperature of about 27°C (80°F) and is ready for use. Commercial growers often add gypsum, at the rate of about 0.45 kg (1 lb) gypsum to 40 kg (88 lb) manure compost—during the first turn—to prevent the finished product from being excessively sticky.
When horse manure is unavailable, you can use other animal manures as a substitute, ready-made mushroom compost, or home-made compost. The latter is made with the aid of an activator. A proprietary brand of this chemical can be bought from your nursery or garden shop. Specific instructions will be provided, but the general principle is simple. Make a heap with alternate layers of straw or any other similar materials suggested, and activator and then follow the same procedure outlined for manure. The heap must also be kept moist but not wet.
Spawning and casing
The spawn, generally shaped fibrous blocks (though now available in granular form) can be bought from nurseries or garden centres. For the spawning of your mushrooms, you need an air temperature of about 21°C (70°F); after covering it can be dropped to about 15°C (60°F). Mushrooms will grow at any temperature above 10°C (50°F), but more slowly at the lower temperatures. Too high temperatures can kill the spawn. This is, of course, more easily maintained within a building than outdoors.
When filling boxes or trays put the compost in firmly, but not packed down hard so that air is completely excluded. Beds and ridges should similarly be packed firmly and evenly, but not trodden—disease can come in on footwear. Ridge beds, which give slightly higher yields from the same floor space, are usually made in pairs. Make the base of the ridges 60 cm (2’) wide, gently tapering at the top to 15 cm (6”). Height should be 45 cm (1-1/2’) from top to base.
When the compost has been put into position, its temperature will again rise, to about 38’C (100°F) and will then gradually fall. Keep the bed moderately well watered during this period—when squeezed, the compost should feel damp but should not drip water. After a few days, the temperature will fall to 21°C (70°F). This is the correct moment to insert the spawn; if the temperature is lower, growth may be very slow.
Break the cake into fragments about the size of a walnut and insert pieces about 2.5 cm (1”) deep in the compost, at a spacing of 20-25 cm (8-10”) in each direction. Press the compost firmly around and over the spawn, so that no air pockets develop.
After a week or so, the mushroom mycelium will be seen spreading like fine greyish to white threads through and on the compost. Leave it for a further ten days, then cover it with a casing of fine, moist soil whose pH is between 7.0 and 8.0. The casing helps to retain the heat of the bed and also helps to conserve moisture. A fine, rich, loamy soil is ideal, and if it has been sterilized, so much the better. Cover the compost evenly to a depth of 2.5 cm (1”). Alternatively, the casing can consist of a mixture of moist peat and chalk or gypsum, in the ratio of three to one by volume.