Mushrooms turn farm wastes, such as cereal straw, sawdust, cotton waste and corn cobs, 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.
That is why mushroom growing suits large commercial farms,
and also smallholders, women's groups and landless households. World production of mushrooms and truffles is over forty million tonnes a year, with China producing by far the largest share.
In this video: what a mushroom really is, which mushroom to grow, preparing the substrate, spawning, the spawn run, fruiting and harvest, keeping moulds and flies out, the numbers, and safety.
We focus on oyster mushrooms, the easiest for a beginner.
A mushroom is only the fruiting body of a fungus.
The main part of the fungus is the mycelium, a network of fine threads, called hyphae, that grows through the substrate and digests cellulose, hemicellulose and lignin with its enzymes.
When the substrate is fully colonised, and conditions change, the mycelium forms mushrooms that release spores.
Different species eat different things.
Oyster, shiitake, paddy straw and wood ear mushrooms are primary decomposers:
they grow on fresh plant material. The button mushroom is a secondary decomposer. It needs substrate that other microbes have already partly broken down, so it grows on composted straw and manure.
Choose a species that fits your climate and your waste.
Button mushrooms fruit at about fourteen to eighteen degrees Celsius, on compost with a casing layer.
Oyster mushrooms grow on straw, sawdust, cotton waste and many other wastes,
and fruit at about fifteen to thirty degrees, depending on the species.
Shiitake grows on hardwood logs or sawdust blocks,
and fruits at about ten to twenty degrees. In the tropics, paddy straw mushrooms grow on rice straw at thirty to thirty-five degrees.
They are a fast crop, but with a short shelf life.
Milky mushrooms also suit hot climates.
For a beginner, oyster is the easiest.
It grows on cheap wastes, tolerates a wide temperature range, needs no casing, and gives high yields.
The substrate is the mushroom's food, and it must be clean, or other moulds will take it over first.
For oyster and paddy straw mushrooms, chop the straw, soak it, and then pasteurise it. A common method is hot water at sixty to seventy degrees Celsius for about an hour, or steam.
Pasteurisation kills most competitors without making the straw sterile.
Other species need more. For shiitake and other sawdust-grown mushrooms,
sawdust mixed with bran is sterilised in bags, in an autoclave or a steam drum.
Button mushroom compost is made from wetted straw and manure in two phases,
first at high temperature outdoors or in bunkers, often seventy to eighty degrees, and then pasteurised and conditioned in a tunnel. Many button farms now simply buy compost that is already spawned and colonised.
Spawn is the mushroom's seed.
It is pure mycelium of a selected strain, grown on sterilised grain.
Good spawn from a reliable laboratory is essential, because contaminated spawn brings its moulds with it.
Mix the spawn into the cooled substrate, or layer it through, usually at two to five per cent of the substrate's wet weight. For oyster mushrooms, the substrate is then packed into bags.
Next comes the spawn run, when the mycelium colonises the substrate.
Keep the bags in the dark, warm and humid.
For oyster and button mushrooms this takes about two to three weeks.
Shiitake on logs takes several months. A good bag is colonised all the way through, as the threads spread out from each grain of spawn.
Button and milky mushrooms need one more step: casing. A layer of moist soil or peat with lime, three to five centimetres deep, is spread over the colonised compost.
Bacteria in the casing, and changes in moisture and carbon dioxide, trigger fruiting.
To make the mycelium fruit, change its world.
Lower the temperature, bring in fresh air to reduce carbon dioxide,
and raise the humidity.
Oyster and shiitake mushrooms also need light.
Mushrooms come in flushes, typically two to four, about a week apart.
Harvest at the right stage.
For button mushrooms, that means before the caps open. Then cool them quickly.
Mushrooms breathe very fast, among the fastest of all fresh produce,
and they spoil within days.
The commonest disaster is a green bag.
Green mould, a Trichoderma fungus, is a major problem in oyster,
shiitake and button mushrooms.
It takes over when the substrate was not properly pasteurised,
the spawn was contaminated, or hygiene and ventilation were poor.
Button mushrooms also suffer dry bubble, wet bubble, cobweb and bacterial blotch. And sciarid and phorid flies, mites and nematodes attack many species.
Control rests on hygiene, not sprays: proper pasteurisation,
clean spawn, filtered air, disinfected rooms and tools, fly screens, and prompt removal of spent substrate.
Very few pesticides are approved for mushrooms.
Growers measure success as biological efficiency: the fresh weight of mushrooms divided by the dry weight of substrate, times one hundred.
Here is the worked example from Laisha's guide. A grower fills bags with one hundred kilograms of dry wheat straw and harvests eighty kilograms of fresh oyster mushrooms over three flushes.
That is a biological efficiency of eighty per cent. Good oyster crops commonly reach about fifty to one hundred per cent.
At two and a half dollars per kilogram, eighty kilograms earns two hundred dollars. The costs per cycle are about sixty-five dollars: ten for straw, thirty for spawn, and twenty-five for bags, fuel for pasteurisation and other items. That leaves about one hundred and thirty-five dollars per cycle before labour, from a small room, and several cycles a year are possible. Your own prices will differ, so do the sum with local numbers.
Why go to this trouble?
Mushrooms are rich in protein on a dry-weight basis,
and in B vitamins, minerals and fibre, while being low in fat. When they are exposed to ultraviolet light, they even produce vitamin D.
And nothing is wasted.
Spent mushroom substrate, what is left after the last flush, is used as a soil conditioner, in compost, as animal feed after treatment, and for biogas. So a mushroom unit fits neatly into a mixed farm:
crop residues go in, food comes out, and the leftovers go back to the soil.
Now, safety.
Cultivate only known species, from reliable spawn. Never eat wild mushrooms unless an expert has identified them, because some deadly species look like edible ones. If a bag grows something you did not plant, do not eat it. Throw it out.
Do not reach for an unapproved spray: very few pesticides are approved for mushrooms, so prevention by hygiene is the answer.
Keep harvested mushrooms cool and sell or eat them within days.
To recap.
A mushroom is the fruit of a mycelium that digests plant waste.
Start with oyster mushrooms.
Chop, soak and pasteurise the straw. Use clean spawn at two to five per cent. Keep the spawn run dark, warm and humid.
Then trigger fruiting with cooler air, fresh air, humidity and light, and harvest in flushes.
Hygiene is your pest control.
And never eat a mushroom you cannot identify. For more on crops, farm enterprises and every pest, visit laisha.ai. Thank you for watching.
