Mushroom growing glossary

Short, plain definitions of the terms used across the species pages, tools and troubleshooting guide.

A

Agar: A jelly-like nutrient medium in Petri dishes or jars on which mycelium is cultured, tested for contamination or multiplied before it is moved to grain. Agar media calculator
Autoclave: A pressure steam sterilizer. Many of the bag trials we cite sterilized substrate at 121 °C for 90 minutes or longer, which is the temperature autoclaves reach. Sterilization calculator

B

Biological efficiency (BE): A measure of yield: the fresh weight of mushrooms harvested from the whole crop divided by the dry weight of the substrate, times 100. A BE of 50% means 500 g of fresh mushrooms from 1 kg of dry substrate. Always check whether a figure covers one flush or the whole crop. Yield and efficiency calculator

C

Cap (pileus): The top part of a mushroom, which carries the spore-bearing surface underneath.
Casing layer: A layer of material, often buffered with lime, spread over colonized compost to help the mushrooms form pins. It is used for the button mushroom and the almond mushroom. Button mushroom · Almond mushroom
CO2 (carbon dioxide): A gas the growing mushrooms and mycelium give off. Trials report its level in parts per million (ppm), for example under 3,000 ppm during incubation and 400–700 ppm during fruiting for maitake. High CO2 during fruiting changes the shape of many species. Long stems, small caps
Cold shock: A deliberate drop in temperature, or a soak in cold water, that triggers a colonized block to start fruiting. Shiitake and sulphur shelf trials used it; the almond mushroom is triggered by lowering the compost temperature. Shiitake
Colonization: The stage in which mycelium grows through and takes over the substrate. It is also called the spawn run. Timeline planner
Contamination: Unwanted organisms such as moulds or bacteria that grow on the substrate or the mushrooms and compete with the mycelium. Troubleshooting guide

D

Dry weight and fresh weight: Fresh weight is what you weigh straight from the bag or the harvest. Dry weight is what remains after the water is dried out. Biological efficiency compares fresh mushroom weight with dry substrate weight.

F

Field capacity: The moisture level a substrate holds after excess water has drained away. NCAT describes it as the point where a hard squeeze yields a few drops, not a stream. Hydration calculator
Flush: One wave of mushrooms from a block or bed. After a flush is picked the substrate rests and a later flush may follow, usually smaller than the first.
Forcing (shocking): Making log-grown shiitake fruit on demand by soaking the logs in cold water for 12–24 hours. The Cornell and NESARE guide uses 24 hours as the standard and aims for two shockings per season. Shiitake
Fresh air exchange (FAE): Replacing CO2-rich air in the growing space with fresh air. It prevents long stems and small caps and is one of the main controls in a fruiting room. Fruiting chamber sizing
Fruiting body: The part of the fungus we call a mushroom, made up of the cap, the stem and the spore-bearing surface.
Fruiting chamber: A space in which humidity, temperature, light and fresh air are controlled so that colonized substrate will form and grow mushrooms. It can range from a tub to a purpose-built room. Fruiting chamber sizing · Climate and humidity calculator

G

Grain spawn: Cooked, sterilized grain colonized by mycelium. It is used to inoculate bulk substrate because it spreads the mycelium evenly through many points. Grain spawn calculator

H

Hyphae: The microscopic threads that make up the body of a fungus. Together they form the mycelium.

I

Incubation: The period after inoculation in which the bags or beds are held, often warm and dark, so the mycelium can colonize the substrate.
Inoculation: Adding spawn, a culture or liquid culture to prepared substrate so that the mycelium can grow in it.

L

Laying yard: The shady, humid outdoor area where inoculated logs are stacked to colonise and fruit, usually with a barrier such as gravel between the logs and the soil.
Liquid culture: Mycelium grown in a sterile nutrient liquid. It is used to inoculate grain or other substrate.

M

Master spawn and planting spawn: Master spawn is the first batch of spawn made from a mother culture. It is used to inoculate a second set of sterilised grain, called planting spawn, which is then used to inoculate the substrate.
Mother culture: A pure culture of one mushroom strain growing on agar or gelatin. It is kept at about 4 °C and sub-cultured every 6–12 months in the University of Florida protocol, and it is used to start spawn. Agar media calculator
Mycelium: The network of hyphae that is the main body of a fungus. It grows through the substrate and produces the mushrooms.

O

Overlay: A thick, fuzzy mat of mycelium that grows over the surface but will not form pins. Overlay

P

Pasteurization: Heat treatment of substrate at a lower temperature than sterilization, which reduces but does not remove all organisms. In one trial, immersing substrate in hot water at 60 °C for 30 minutes made it unfavourable to green mould. Sterilization calculator
Pin (primordium): The very first small bump from which a mushroom grows. Pins that stop developing are called aborts. Aborts

R

Relative humidity (RH): How much water vapour the air holds compared with the most it could hold at that temperature, as a percentage. Fruiting rooms for most species are kept in the 80–95% range.
Ruffling: Mixing the mycelium that has grown into the casing layer through the whole depth of the casing. In an almond mushroom trial it raised biological efficiency by 21%. Almond mushroom

S

Saprotroph: An organism that feeds on dead organic matter. Most cultivated mushrooms are saprotrophs growing on wood, straw or compost.
Spawn: Mycelium growing on a carrier such as grain or sawdust, used to start a new batch of substrate.
Spawn rate: The amount of spawn added to the substrate, usually given as a percentage of weight. Trials we cite used 2% for shiitake and 3% of dry substrate weight for reishi. Spawn ratio calculator
Spent substrate: What remains after the mushrooms have been harvested. It can be composted or used as soil improver.
Squeeze test: A hand check of substrate moisture. Squeeze a handful of mixed, damp substrate: it should hold together and release only a little water. Agrodok 40 targets 60–65% moisture after mixing for oysters, and notes that water collecting at the bottom of a bag means the substrate is too wet.
Sterilization: Treating substrate or equipment so that no living organisms remain, usually with pressurized steam. It gives mycelium a clean start but means any later contamination meets no competition. Sterilization calculator
Stipe: The stem of a mushroom.
Strain: A particular genetic line of a species. Strains of the same species can differ in temperature range, yield and speed, so published figures are starting points to check for your own strain.
Substrate: The material the mycelium feeds on, for example straw, sawdust, compost or grain. Substrate recipe calculator
Supplement: A nutrient-rich material, such as wheat bran, added to substrate to raise yield or shorten the time to the first harvest. Trials report that added bran can shorten the time to first harvest.
Synthetic log: A block of sawdust and supplements in a bag, used in place of a natural log to grow wood-loving species such as shiitake or sulphur shelf. Sulphur shelf

T

Tissue culture (cloning): Making a pure culture by placing a piece of clean inner tissue from a fresh mushroom on agar or gelatin so that the mycelium grows out of it.

Last updated: 2026-10-19