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Lesson 1 of 9 · 11 min

Mushrooms crash course: what they are, how they grow, the main types

A mushroom is only the fruit of a fungus. The real organism is the mycelium, a web of fine white threads living inside its food. This 11-minute crash course explains how mushrooms grow and why climate decides every harvest.

Safety. Hot water and steam cause burns. Use heat-resistant gloves and eye protection. Never eat a wild mushroom because a video said it is safe.

Key points

What a mushroom really is

  • A mushroom is only the fruit of a fungus. The living fungus is the mycelium: a web of fine white threads growing inside its food.
  • That food is called the substrate: straw, sawdust, compost or grain.
  • Mushrooms have no chlorophyll, so they cannot make food from sunlight like green plants.
  • Instead, the mycelium releases enzymes that break down the substrate, then absorbs the nutrients.

The growing cycle, step by step

  • Spawn: sterilised grain that already carries the mushroom's mycelium. It works like the "seed" of mushroom growing.
  • Spawn is mixed into the prepared substrate.
  • Spawn run: the mycelium spreads through the substrate until it is fully white.
  • Pinning: tiny baby mushrooms, called pins, appear.
  • Fruiting and harvest: pins grow into mushrooms and are picked.
  • The same substrate gives several harvests in waves, called flushes.
  • Preparing the substrate
  • Straw is chopped into pieces of 2–5 cm and wetted to 65–70 % moisture.
  • Too wet is harmful: at 85–95 % moisture there is not enough air, and the mycelium suffocates.
  • Straw for oyster and milky mushrooms is pasteurised: hot water at 80–85 °C for 2 hours. This weakens competing microbes.
  • Sawdust and grain for shiitake, king oyster, lion's mane and cordyceps are sterilised: steam under pressure at 121 °C for about 1 hour.

Why climate matters at every stage

  • The mycelium and the mushroom want different climates. During spawn run the mycelium likes warmth and tolerates stale air. To fruit, most mushrooms need fresh air, high humidity and often a cooler room.
  • Example, button mushroom: spawn run at 23 ± 1 °C with carbon dioxide at 12,000–15,000 ppm. In the first week after the casing layer goes on: 24 ± 1 °C, 95 % humidity, 7,500 ppm carbon dioxide. Then, to fruit: air at 15–17 °C, 85 % humidity, and carbon dioxide down to 800–1,000 ppm.
  • What happens when the climate drifts
  • Oyster mushroom: when carbon dioxide rises above 600 ppm, stems stretch and caps stay small.
  • Shiitake: dry conditions make the caps crack.
  • Green mould, called Trichoderma, is one of the most common competitors. Clean rooms, clean tools and clean hands help keep a crop healthy.

Oyster and button, the two classics

  • Oyster mushroom (Pleurotus)
  • Grows on straw and many other plant wastes.
  • About 4–5 weeks from spawning to harvest.
  • Fruits between 10 and 28 °C, depending on the strain: cool strains at 12–15 °C, medium strains at 16–22 °C, warm strains at 20–26 °C.
  • Needs 85–90 % air humidity while fruiting.
  • Button mushroom (Agaricus bisporus)
  • Grows on compost, covered with a "casing": a 4 cm layer of moist soil-like material that helps it fruit.
  • Needs a cool, carefully controlled room to fruit (numbers in Section 3).
  • Portobello and crimini are the same species: brown button mushrooms grown to maturity.

Heat lovers: milky and paddy straw

  • Milky mushroom (Calocybe indica)
  • Grows on straw and also needs a casing layer, 2–5 cm thick.
  • Fruits at 30–35 °C with 80–90 % humidity.
  • After harvest it keeps better than oyster or button mushrooms.
  • Paddy straw mushroom (Volvariella volvacea)
  • The fastest crop: the first harvest comes 9–10 days after spawning, and the whole cycle takes 4–5 weeks.
  • During spawn run the bed is kept covered with plastic at 30–35 °C and 80–85 % humidity.
  • After the cover comes off: 28–32 °C and about 80 % humidity.

Wood lovers: shiitake and king oyster

  • Shiitake (Lentinula edodes)
  • Grown on hardwood logs outdoors, or on sawdust blocks in climate-controlled rooms.
  • A log needs 6–18 months before its first mushrooms.
  • To start fruiting, logs are soaked in cold water for 12–24 hours.
  • Soaking works when average night temperatures stay above 10 °C.
  • King oyster (Pleurotus eryngii)
  • Grows on sterilised sawdust in bottles or bags.
  • The mycelium grows in the dark at 25 ± 1 °C.
  • Fruiting happens in a cool room at 15 ± 2 °C with 80 ± 5 % humidity.

Lion's mane and cordyceps

  • Lion's mane (Hericium erinaceus)
  • Grows on sterilised sawdust or crop waste.
  • Mycelium grows best at 21–24 °C.
  • Fruits between 10 and 24 °C, with 85–95 % humidity and gentle light of 200–400 lux.
  • Cordyceps militaris (bright orange, finger-like)
  • Grown on grain, such as brown rice, in jars of about 500 ml.
  • First 1–2 weeks in the dark at 19–21 °C.
  • Then light turns on: 500–1,000 lux for 8–12 hours a day, at 16–23 °C and 70–95 % humidity.
  • The crop is ready in 35–40 days.

Match the mushroom to your climate

  • Warm conditions suit paddy straw mushroom (28–32 °C), milky mushroom (30–35 °C) and warm oyster strains (20–26 °C).
  • Cooler conditions suit button mushroom (15–17 °C), king oyster (15 ± 2 °C), cool oyster strains (12–15 °C) and lion's mane (10–24 °C).
  • Shiitake logs fruit when nights stay above 10 °C.
  • Or grow in a room that holds the right climate for each stage. That is why growers watch temperature, humidity, fresh air and light so closely.