Reference

Mushroom growing terms, explained plainly

Updated 2026-10-26

Mushroom growing has its own words, but the ideas are simple. Mycelium is the living network that eats the food you give it. Spawn is mycelium grown on grain, used to seed a bigger batch of substrate, which is the food. Colonization is the mycelium filling that food. Pinning is when tiny mushrooms appear. A flush is one wave of mushrooms. Below are the terms you will meet most, grouped by when you meet them.

What are the basic parts of a mushroom?

Mycelium: The white, thread-like network that grows through food and digests it. It is the main body of the fungus. Mushrooms are its fruit.
Hyphae: The single threads that make up mycelium.
Fruiting body: The mushroom itself: cap, gills or spines, and stem. It exists to spread spores.
Spores: Tiny cells a mushroom releases, a bit like seeds. Home growers of culinary mushrooms rarely start from spores, because a culture is faster and more reliable.
Spore print: The pattern left when a cap drops spores on paper or foil. Used to help identify mushrooms.
Strain: A line of one species with its own traits, such as speed, color, or temperature range.

What do spawn, substrate, and culture mean?

Culture: Living mycelium kept for starting new grows. It can be on agar or in liquid.
Liquid culture: Mycelium growing in sterile sugar water, used to inoculate grain.
Agar: A jelly in a dish used to grow and clean up cultures.
Inoculation: Adding a culture or spawn to sterile grain or substrate to start it growing.
Spawn: Mycelium grown on a carrier, usually grain, then mixed into a larger batch of substrate. Grain spawn is the most common kind.
Spawn rate: How much spawn you mix in, compared with substrate. More spawn colonizes faster and leaves less room for mold.
Substrate: The food the mycelium eats and fruits from: hardwood sawdust, straw, compost, or a mix.
Supplemented sawdust: Hardwood sawdust with added bran or soy hulls for more food. It gives bigger yields but needs sterilizing.
Pasteurization: Heating substrate enough to kill most competitors but not all. Common for straw.
Sterilization: Heating under pressure to kill everything. Needed for grain and rich substrates.
Field capacity: Substrate as wet as it can be without water dripping out when squeezed.

What are the stages of a grow called?

Colonization: The mycelium spreading through the substrate until it is white throughout. Usually warm and dark.
Fully colonized: White all the way through, with little substrate showing. The point to start fruiting.
Pinning: When tiny mushrooms, called pins, first form. It needs a change: cooler air, more fresh air, high humidity, and light.
Primordia: Another word for pins: the first knots of a mushroom.
Fruiting: Pins growing into full mushrooms.
Flush: One wave of mushrooms. Most blocks give two or three, each smaller than the last.
Browning: A shiitake stage where the block surface turns brown and tough before it fruits.
Cold shock: A short spell of cold, or a cold soak, that tells some species to fruit.
Soaking: Putting a block in cold water for some hours between flushes to put back moisture.

In Shiitake's profile, browning lasts 21 days and the cold shock runs at 16 °C (61 °F). Every species page lists each stage.

What do growing setup terms mean?

Fruiting block: A bag or block of colonized substrate ready to fruit. Most kits are fruiting blocks.
All-in-one bag: A grow bag with grain and substrate in one, colonized in the same bag.
Filter patch: The small square on a grow bag that lets air in and keeps mold spores out.
Monotub: A plastic tub with holes, used as a simple fruiting chamber for bulk substrate.
Martha tent: A small greenhouse shelf with a plastic cover, used to hold humidity around several blocks.
Casing layer: A layer of damp peat or similar on top of substrate. Button mushrooms need it to pin.
Side fruiting: Mushrooms growing from the sides of a bag or tub, often where light or air gets in.
Smart chamber: An enclosed grower that controls humidity, light, and fresh air on its own. Some also manage temperature.

What do air and humidity terms mean?

Humidity: How much water the air holds, as a percent of the most it could hold at that temperature. Fruiting mushrooms usually want 80 to 95%.
Fresh air: Air changes that clear carbon dioxide. Short for fresh air exchange.
Carbon dioxide: The gas mushrooms breathe out. High levels give long stems and small caps.
Hygrometer: A meter that reads humidity. Cheap ones are often off by a few percent.
Misting: Spraying fine water on chamber walls to raise humidity.

For example, Pearl Oyster fruits at 88% humidity in its profile. Read humidity and fresh air for mushrooms for more.

What do problem terms mean?

Contamination: Anything growing in your substrate that is not your mushroom: mold or bacteria. See mushroom contamination.
Trichoderma: A common green mold that takes over substrate.
Cobweb mold: A gray, wispy mold that spreads very fast.
Bacterial blotch: Yellow or brown sticky spots on caps, often from standing water.
Metabolites: Yellow or amber drops the mycelium makes. Normal, not mold.
Leggy: Long, thin stems with small caps, usually from too little fresh air. See leggy mushroom stems.
Aborts: Pins that stop growing and dry out, often from low humidity.

FAQ

What is the difference between spawn and substrate?

Spawn is mycelium already growing on grain, used like a starter. Substrate is the bigger batch of food, such as sawdust or straw, that the spawn colonizes and fruits from.

What does fully colonized mean?

The substrate is white with mycelium all the way through and feels firm. That is the point to start fruiting conditions.

What is a flush of mushrooms?

One wave of mushrooms from a block. After a harvest the block rests, then can give another, usually smaller, flush.

What are pins in mushroom growing?

Pins are the first tiny mushrooms that form on a colonized block. They grow into full mushrooms over the next few days.