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How to grow oyster mushrooms at home on straw

Oyster mushrooms are the best place for a beginner to start. They grow fast on cheap materials such as straw, maize stalks and coffee grounds, they need no sunlight and no soil, and they forgive mistakes more than any other kind.

Choose the kind for the season

Different oyster mushrooms like different temperatures. Grey or blue oysters fruit best at about 12 to 20 °C and suit a cool season, such as winter on the Highveld. Pink and golden oysters suit warm weather. Matching the kind to the season lets you harvest for most of the year.

Buy fresh spawn from a reputable supplier, or learn with a ready-made kit first.

Step 1: prepare the straw

1. Chop clean wheat straw into pieces 5 to 10 cm long. Wear a dust mask.
2. Remove stones, string and mouldy clumps.
3. Weigh the dry straw. One kilogram of dry straw makes about 3 kg of wet substrate.

Never use sawdust from treated timber, mouldy material, or straw that was recently sprayed.

Step 2: pasteurise it

Pasteurising kills most moulds and harmful bacteria, which would otherwise win the race for the food. There are two common ways.

Hot water

1. Work outdoors, with a clean metal drum on a stable burner.
2. Heat the water to about 75 °C, measured with a thermometer.
3. Submerge the straw in a mesh bag, weighted down.
4. Hold the water between 65 and 80 °C for one to two hours, checking every 15 minutes.
5. Lift the bag out with a helper, wearing long rubber gloves, and let it drain on a clean surface.
6. Cool it to below 30 °C before adding spawn. Hot straw kills spawn.

Hydrated lime, which needs no heat

1. Wear goggles, rubber gloves and a dust mask.
2. Add hydrated lime (builders' lime) to a drum of clean water, never water to lime. A common recipe is 2 to 3 g for each litre of water.
3. Soak the straw in a weighted mesh bag for 12 to 24 hours.
4. Drain it. Dispose of the limewater carefully, because it is caustic, and never into a stream.

Either way, the straw is ready when a handful squeezed hard gives a few drops, not a stream.

Step 3: add spawn and fill the bags

1. Mix the spawn through the cool, drained straw with clean hands, at the rate your supplier recommends.
2. Pack it firmly into clear plastic growing bags, about two-thirds to three-quarters full, and tie the top tightly. A typical bag holds 3 to 5 kg.
3. Make small slits or pinholes about 10 to 15 cm apart all over the bag.
4. Label each bag with the date.

A food-grade 20-litre bucket with 1 cm holes drilled round the sides also works, and can be reused for years.

Step 4: leave them to colonise

Keep the bags in a warm, dark place at about 20 to 24 °C, and leave them alone. Over two to four weeks, white growth spreads through the straw until the bag is a firm white block.

Check through the plastic without opening the bags. If you see any colour that is not white, especially bright green, remove that bag at once. Do not open it indoors.

Step 5: fruit them

Fruiting needs three things together: high humidity, plenty of fresh air and indirect light.

1. Cut X-shaped slits of 3 to 5 cm in the sides of the bag.
2. Move the bag somewhere cooler with fresh air and indirect light.
3. Mist the air and the surfaces around the bags at least twice a day. Do not let water pool on the caps.

Pins usually appear within three to seven days, and the mushrooms grow remarkably fast after that. Harvest the whole cluster when the edges of the largest caps are just flattening. After a rest, the bag may give a second and a third crop.

Safety

Grow in a ventilated space, not in a bedroom or living room, because mushroom spores can irritate the lungs.

This guide is based on Chapters 4, 6, 7 and 8 of Growing Mushrooms at Home.