Mushroom cultivation
Growing button, oyster, shiitake and paddy straw mushrooms: substrates, spawn, the crop cycle, hygiene, economics and biological efficiency.
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Mushrooms turn agricultural wastes, such as cereal straw, sawdust, cotton waste, corn cobs and manure, into protein-rich food in a few weeks, on very little land and often indoors. The leftover substrate becomes a soil conditioner or animal feed. This makes mushroom growing attractive both for large commercial farms and for smallholders, women's groups and landless households.
FAO statistics put world production of mushrooms and truffles at over 40 million tonnes a year, with China producing by far the largest share. Mushroom biology and cultivation are part of horticulture and plant pathology courses and exams.
What mushrooms are
A mushroom is the fruiting body of a fungus, mostly in the Basidiomycota. The main part of the fungus is the mycelium, a network of hyphae that grows through the substrate, digesting cellulose, hemicellulose and lignin with its enzymes. When the substrate is colonised and conditions change, the mycelium forms fruiting bodies that release spores.
Different species decompose different materials:
- Primary decomposers (white-rot fungi) grow on fresh plant material: oyster (Pleurotus), shiitake (Lentinula edodes), paddy straw (Volvariella volvacea), wood ear (Auricularia), enoki (Flammulina).
- Secondary decomposers need substrate already partly broken down by other microbes: the button mushroom (Agaricus bisporus) grows on composted straw and manure.
Major cultivated species
| Species | Substrate | Temperature for fruiting | Notes |
|---|---|---|---|
| Button (Agaricus bisporus) | composted straw and horse or poultry manure, with casing | about 14–18 °C | the main mushroom in Europe and North America; includes white button, chestnut and portobello |
| Oyster (Pleurotus spp.) | straw, sawdust, cotton waste, many agricultural wastes | about 15–30 °C depending on species | easiest to grow, high biological efficiency |
| Shiitake (Lentinula edodes) | hardwood logs or supplemented sawdust blocks | about 10–20 °C | major in East Asia; long spawn run |
| Paddy straw (Volvariella volvacea) | rice straw, cotton waste | about 30–35 °C | tropical; fast crop but short shelf life |
| Milky (Calocybe indica) | straw with casing | about 30–35 °C | grown in hot climates |
| Wood ear (Auricularia spp.) | sawdust, logs | about 20–30 °C | widely grown and dried in China |
The production cycle
Substrate preparation
- For button mushrooms, straw and manure are wetted and composted in two phases: Phase I outdoor or bunker composting at high temperature (often 70 to 80 °C), then Phase II pasteurisation and conditioning in a tunnel, removing ammonia and pests. Many farms now buy Phase III compost already spawned and colonised.
- For oyster and paddy straw, chopped straw is soaked and pasteurised, for example in hot water at 60 to 70 °C for an hour or by steam, or treated chemically; in some systems it is sterilised.
- For shiitake and other sawdust-grown species, sawdust supplemented with bran is sterilised in bags in an autoclave or steam drum.
Spawn and spawning
Spawn is pure mycelium of a selected strain grown on sterilised grain. Good spawn from a reliable laboratory is essential; it is mixed into or layered through the substrate, usually at 2 to 5 per cent of the substrate's wet weight.
Spawn run
The mycelium colonises the substrate in the dark at warm temperatures and high humidity, over about two to three weeks for oyster and button mushrooms and several months for shiitake on logs.
Casing (for button and milky mushrooms)
A 3 to 5 cm layer of moist casing soil or peat with lime is spread over colonised compost. Bacteria in the casing and changes in moisture and CO2 trigger fruiting.
Pinning and cropping
Fruiting is triggered by lowering temperature, introducing fresh air (reducing CO2), raising humidity and, for oyster and shiitake, giving light. Mushrooms appear in flushes, typically two to four, about a week apart. They are harvested at the right stage, before caps open for button mushrooms, and cooled quickly, since mushrooms respire very rapidly and spoil within days.
Pests, diseases and hygiene
- Competitor moulds: green mould (Trichoderma) is a major problem in oyster, shiitake and button cultivation.
- Diseases: dry bubble, wet bubble and cobweb in button mushrooms; bacterial blotch.
- Pests: sciarid and phorid flies, mites, nematodes.
Control relies on hygiene: proper pasteurisation, clean spawn, filtered air, disinfected rooms and tools, fly screens and prompt removal of spent substrate. Few pesticides are approved for mushrooms.
Biological efficiency and income from oyster mushrooms
Biological efficiency (BE) = fresh weight of mushrooms ÷ dry weight of substrate × 100.
A grower fills bags with 100 kg of dry wheat straw and harvests 80 kg of fresh oyster mushrooms over three flushes:
- BE = 80 ÷ 100 × 100 = 80 per cent. Good oyster crops commonly achieve about 50 to 100 per cent; well-managed button mushroom farms harvest roughly 25 to 35 kg of mushrooms per 100 kg of compost.
Income. At 2.50 dollars per kg, 80 kg earns 200 dollars. Costs per cycle: straw 10 dollars, spawn (5 per cent of a wet substrate weight of about 300 kg, so 15 kg at 2 dollars) 30 dollars, bags, fuel for pasteurisation and other items 25 dollars: total 65 dollars, leaving 135 dollars per cycle before labour, from a small room. Several cycles a year are possible.
Value and uses
Mushrooms are rich in protein (on a dry basis), B vitamins, minerals and fibre, and low in fat; when exposed to ultraviolet light they produce vitamin D. Spent mushroom substrate is used as a soil conditioner, in compost, as animal feed after treatment, and for biogas.
Key points
- Mushrooms are fruiting bodies of fungi; the mycelium digests plant wastes.
- Main species: button (Agaricus, compost and casing), oyster (Pleurotus, straw), shiitake (Lentinula, logs and sawdust), paddy straw (Volvariella), milky (Calocybe), wood ear (Auricularia).
- Cycle: substrate preparation and pasteurisation or sterilisation, spawning, spawn run, casing (button), pinning and cropping in flushes.
- Hygiene controls moulds, diseases and flies.
- Biological efficiency = fresh mushrooms ÷ dry substrate × 100; oyster often 50–100 per cent.
What the exams ask
- School-leaving and entrance papers: types of edible mushrooms, and basic steps of cultivation.
- Degree and research-fellowship entrances: substrates and composting, spawn production, environmental requirements, casing, pests and diseases, and biological efficiency.
- Professional and entrepreneurship examinations: planning a mushroom unit, economics, post-harvest handling, and uses of spent substrate.
Described in general terms: the kind of examination, not a past paper. Laisha never reproduces exam questions.
Questions people ask
Which mushroom is easiest for beginners?
Oyster mushrooms: they grow on many cheap wastes, tolerate a wide temperature range, need no casing, and give high yields.
Are wild mushrooms safe to cultivate or collect?
Cultivate only known species from reliable spawn. Never eat wild mushrooms unless identified by an expert: some deadly species look like edible ones.
Why did my bags turn green?
Green mould (Trichoderma) took over, usually because the substrate was not properly pasteurised, the spawn was contaminated, or hygiene and ventilation were poor.
Sources
- Chang, S. T. and Miles, P. G. Mushrooms: Cultivation, Nutritional Value, Medicinal Effect, and Environmental Impact, 2nd edition. CRC Press, 2004.
- Stamets, P. Growing Gourmet and Medicinal Mushrooms, 3rd edition. Ten Speed Press, 2000.
- Zied, D. C. and Pardo-Giménez, A. (eds) Edible and Medicinal Mushrooms: Technology and Applications. Wiley-Blackwell, 2017.
- FAO. FAOSTAT: Crops and livestock products, mushrooms and truffles. FAO, online.
- Royse, D. J., Baars, J. and Tan, Q. "Current overview of mushroom production in the world." In Zied, D. C. and Pardo-Giménez, A. (eds) Edible and Medicinal Mushrooms, 5–13. Wiley-Blackwell, 2017.
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