Publications
The Garden
November 2004
Fungi to feast upon
Gourmet mushrooms are easy to grow, environmentally friendly, tasty and good for you. Is it the traditional British suspicion of ‘toadstools’ that is preventing their wider cultivation? asks Jon Ardle
Images: Tim Sandall
Animal, vegetable or mineral? In the case of mushrooms, the answer is none of the above, for they are the fruiting bodies of fungi, and fungi are not plants but have a kingdom of their own. Lacking chlorophyll, fungi gain the energy they need for growth from other organisms, living or dead, playing a central role in recycling deceased animals and plants, making their nutrients available to living organisms. They are key components in virtually all soils and compost heaps.
To most UK gardeners however, fungi mean problems - rusts, mildews and blackspot that sap the vigour and ruin the appearance of plants, fairy rings in turf and tree-killing honey fungus. In mythology and literature, ‘toadstools’, appearing seemingly by magic overnight, are reviled for their toxic or hallucinogenic effects and are seen as unearthly, even evil. In Europe and Asia, by contrast, a range of wild mushrooms are avidly collected and eaten with enthusiasm.
Over the last two decades, the worldwide production of edible fungi has increased hugely, particularly in China, where the industry employs more than 10 million people. Shiitake (Lentinula edodes) and oyster mushrooms (Pleurotus species), two of their major crops, have become relatively common in UK supermarkets and delicatessens.
For how to grow shiitake mushrooms, click here.
For how to grow oyster mushrooms, click here.
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Harvesting fresh shiitake mushrooms from an inoculated birch log. A full-flavoured Oriental species, shiitake are one of the most popular exotic mushrooms and surprisingly easy to grow. |
As alternative vegetables, mushrooms are nutritious, high in protein and vitamins and low in fat. Research in China is proving the tradition of using fungi for medicinal reasons has a sound basis: shiitake can reduce both cholesterol and high blood pressure, and extracts are being studied for their anti-cancer and antibiotic properties.
While ‘gourmet’ mushrooms are becoming more familiar, few gardeners seem to realise how easy and rewarding they are to grow. Specialist suppliers now offer a range of starter cultures or spawn that can be grown on logs, woodchips, straw or even waste paper with minimal effort, indoors or out.
Edible fungi
Despite their bad press, fungi have long been integral to human life. Yeasts, single-celled fungi, have brewed beer and made bread rise for thousands of years, and the fruiting bodies of some species have probably been consumed for much longer than that.
The majority of higher fungi, the multicellular species that produce specialised fruiting bodies (mushrooms) for releasing their spores, are either true saprophytes, colonising only dead material, or are those that grow in association with the roots of plants to their mutual benefit in symbiotic relationships. The latter, mycorrhizal fungi, produce some of the most expensive and sought after mushrooms such as chanterelles and truffles but have resisted most attempts to cultivate them. Relatively few ‘toadstools’ are parasitic on living organisms.
Growing methods
Commercial mushroom cultivation has become increasingly efficient, using strains selected for high yield and vigour, grown on sterilised substrates to reduce competition from undesirable weed fungi. Home growers can take advantage of such developments but simpler growing methods can work just as well. Success is more certain than collecting from the wild, and there is no danger of mistaking a poisonous species for an edible one.
The earliest attempts to grow mushrooms at home were probably either scattering spores or crumbling mushrooms over grassy areas, or transplanting pieces of turf from which mushrooms had appeared, inevitably with hit-and-miss results.
Only button mushrooms, Agaricus bisporus, have been grown on any scale in the West. Probably the biggest advance in growing other edible species came in 1933, with the discovery that pure, uncontaminated cultures could be raised on sterilised grain. Most specialist suppliers now offer grain spawn, or cultures raised on sawdust. Because the fungus is already in vigorous growth, it establishes much more quickly than from spores and there are no competitor fungi or bacteria present.
Whatever method is chosen, growing mushrooms is a three-step process:
- A suitable substrate is prepared and inoculated with the chosen fungus, whether from spores or a cultured spawn.
- The thread-like growths (hyphae) that make up the body of the fungus (its mycelium) is given the time and growing conditions to colonise the substrate (the spawn run).
- In response to changing environmental conditions, the mycelium forms tiny ‘buds’ (primordia), which develop into small mushrooms and grow to harvestable size.
Broadcast-sowing in grass
Some suppliers offer cultures of turf-colonising species such as field mushroom, parasol (Lepiota procera), and shaggy inkcap (Coprinus comatus). These can be sown in patches by peeling back an area of unfertilised turf (chemical fertilisers discourage the growth of most fungi), scattering grain spawn over the soil and replacing the grass. Moist and semi-shaded sites are favoured, and a spring ‘sowing’ can produce mushrooms the following autumn. While it can be productive, success is not guaranteed as there are simply so many poorly-understood factors that affect the establishment and growth of fungi, (let alone what induces them to form fruiting bodies). Dried spawn is not in active growth when broadcast, so is probably even less certain of success.
Growing on logs
Raising wood-colonising, saprophytic fungal species on cut logs is a technique thought to have been developed in China around 1000AD for shiitake, a meaty, smoky-flavoured mushroom long popular in China and Japan as both food and medicine. Pre-inoculated logs are available from some suppliers but postage costs can be high, so most growers inoculate their own logs with grain spawn or short lengths of dowel colonised by spawn.
Hardwood logs around 10-15cm (4-6in) in diameter are preferred, with oak, birch, beech, maple, ash, willow and poplar all favoured. Few mushrooms will grow on softwoods, although Pleurotus pulmonaria (an oyster fungus also known as phoenix mushroom) is happy on spruce and fir.
It usually takes the fungi several months to colonise logs and begin fruiting, during which time they should be kept shaded and moist. Logs of dense woods such as oak can produce flushes of mushrooms for six years.
Log cultivation suits a range of fungi especially oyster mushrooms (Pleurotus species), lion’s mane (Hericium erinaceus), king stropharia (Stropharia rugosoannulata, a large, tasty mushroom), chicken of the woods (Laetiporus sulphureus), and the Oriental species known as nameko (Pholiota nameko, slimy-capped but nutty and crunchy), maitake or hen of the woods (Grifola frondosa, another meaty, tasty species) and reishi (Ganoderma lucidum, widely grown in Asia for medicinal and, allegedly, aphrodisiacal properties). A few logs of each of these would produce a true gastronomes’ selection.
Tree stumps can also be an excellent substrate for these species of fungi, although results with shiitake have been variable. Not only does this produce an edible crop over a longer period than from a narrower log, the fungi break down the stump much more quickly than would otherwise be the case, and once established they should reduce the possibility of honey fungus (itself an edible species but not one to be encouraged into the garden) colonising the stump and spreading to healthy plants.
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Nameko is a Japanese species that grows well on sawdust. The caps’ natural sliminess disappears during cooking. |
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Not at all fussy about their substrate, oyster mushrooms will happily grow on paper, and kits are available for raising them on toilet rolls. |
Broadcast-sowing on wood chips
Growers, particularly in the USA, have experimented with broadcast-sowing spawn onto fresh woodchips. Known as ‘mound cultivation’, this makes a much greater wood surface area available to the fungus for initial colonisation, making establishment far quicker than on logs. The size of chips produced by garden shredders are ideal and most hardwoods are suitable, so pruning waste can be recycled into a tasty crop. Some 1.6 million tonnes of wood waste is disposed of in British landfill sites every year, much of which could be used to raise mushrooms, breaking the wood down into rich compost in the process.
Again a semi-shaded position is preferred and the mound must be kept moist, but an obvious area for application is on bark and wood mulches used around plants or on paths (although most commercially available bark chippings are of softwoods). It may also be worth trying to inoculate compost heaps, providing they contain plenty of wood.
Paul Stamets, a US grower, reports he has had heavy crops of king stropharia and oyster mushrooms from a bed of a 50-50 mix of sawdust and wood chips 10cm (4in) thick. Both species are vigorous saprophytes but do not attack living plants (avoid Pleurotus eryngii, king oyster, outdoors: it can be parasitic).
Sawdust and straw
In pursuit of higher and more rapid yields, commercial growers in the Far East found in the 1950s and 1960s most wood-growing fungi can be raised on sawdust, colonising the high surface area much more quickly than logs or chips. Yields increased even more using sawdust sterilised before inoculation to remove competitors, and supplemented by high-nitrogen additives such as bran.
Commercial production of a range of fungi popular in the Far East is now largely based on this method. Temperature, lighting and humidity are all controlled in large growing rooms, and the mycelia grow quickly, the spawn run taking between four and 15 weeks, compared to eight months to a year in log cultivation. This is a remarkably efficient growing system: 100kg of logs can produce 10-15kg of fresh mushrooms, spread over up to six years, whereas 100kg of supplemented sawdust can produce 80kg or more of mushrooms in five to eight months.
All the species suitable for log growing can be grown on improved sawdust, with suppliers offering kits tailored to each. Some fungi, particularly oyster mushrooms, will colonise virtually any organic substance containing lignin or cellulose. Oysters are commonly cultivated on straw, but can be successfully grown on newspaper, cardboard or even toilet rolls, as well as waste products such as coffee grounds, corn cobs, bagasse (sugar cane residue) and a host of others. Oysters are also vigorous enough to out-compete most ‘weed’ fungi species, and as such are one of the best choices for the novice mushroom grower. They do however need light to develop properly; in darkness they form ill-defined, leggy, coral-like structures. Perhaps their one drawback is the huge numbers of spores they release, to which some people are allergic, so oysters are best not grown in a confined space.
Whether you want to recycle your logs and stumps, make better use of the chips from your shredder, seed your lawn with edible fungi, have space for a few bags of sawdust or straw in a shed or outhouse, or simply treat your palate, it has never been easier to grow gourmet fungi. Mushrooms are nutritious, healthy, sometimes quite beautiful, come in a range of flavours and textures, and are increasingly available from some of the large seed companies as well as specialist suppliers. Perhaps we should be asking why it has taken so long for toadstools to be offered to the home grower?
Jon Ardle is Features Editor for The Garden and a mushroom enthusiast
For how to grow shiitake mushrooms click here.
For how to grow oyster mushrooms click here.
Further reading
Growing Gourmet and Medicinal Mushrooms, 3rd Edition by Paul Stamets, Ten Speed Press, 2000, £40, ISBN 1580081754
Edible and Poisonous Mushrooms of the World by Ian Hall et al, Timber Press, 2003, £29.99, ISBN 0881925861
Suppliers of spawn and growing kits
Anne Miller’s Speciality Mushrooms, Aberdeen; 01467 671315; www.annforfungi.co.uk
The Organic Gardening Catalogue, Surrey; 0845 130 1304; www.organiccatalogue.com
Suttons; 0870 2200606; www.suttons-seeds.co.uk
Dobies; 0870 1123625; www.dobies.co.uk
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