Glossary

Mushroom growing glossary

The words growers use, from spawn to flush, each in a sentence or two. Terms with their own page explain how to do it, measure it or spot it.

A

Aborts: Aborts are pins or young mushrooms that stop growing before they mature. They stay small and often darken. A few are normal; a lot of them usually means the air was too dry, too stale or too hot while the block was pinning.
Agar: Agar is a jelly made from red seaweed that mushroom growers mix with nutrients such as malt extract, sterilize and pour into petri dishes or tubes. Mycelium grows across its clear surface, so growers use agar plates to start, test, clean up and store cultures. More on agar →

B

Bacterial contamination: Bacterial contamination is bacteria growing in a mushroom culture, spawn or crop. In grain it shows as wet spot or sour rot: wet, grey, slimy kernels that smell sour. On mushrooms it shows as bacterial blotch, yellow-to-brown spots on caps that stayed wet. More on bacterial contamination →
Break and shake: Break and shake is breaking up partly colonized grain spawn through the closed jar or bag, then shaking it so colonized kernels spread among bare ones. Each moved kernel starts a new patch of growth, so the grain finishes colonizing sooner. More on break and shake →

C

Casing layer: A casing layer is a top-dressing of moist, low-nutrient material, usually peat moss buffered with limestone, spread over colonized substrate to make the mycelium switch from growing to fruiting. It also holds water for the developing mushrooms. Button mushrooms need one, and king oyster yields more with one. More on casing layer →
Cobweb mold: Cobweb mold is a fungal disease of cultivated mushrooms, caused by Cladobotryum species, that grows as loose, wispy, white to grey tufts over the substrate, pins and caps. It feeds on mushroom fungi, spreads fast in still, humid air, and can cover a jar or tub in a day or two. More on cobweb mold →
Colonization: Colonization is mushroom mycelium growing through grain or substrate until it covers and binds all of it. A jar, bag or block is fully colonized when no bare grain or substrate is left, which is the signal to spawn it to bulk or move it into fruiting conditions. More on colonization →
Contamination: Contamination in mushroom growing is any unwanted organism, usually a mold or bacteria, growing in your culture, spawn, substrate or mushrooms and competing with the mushroom mycelium. It can stall colonization, ruin a flush or kill a block, and it spreads easily in the humid conditions mushrooms need. More on contamination →
CVG: CVG is a substrate mix of coco coir, vermiculite and gypsum, hydrated and pasteurized before use. It holds water well but has few nutrients, so gourmet growers mostly use it as a casing layer rather than as food for the mushroom.

F

Field capacity: Field capacity is the most water a mushroom substrate can hold without free water pooling or dripping out of it. Squeezed hard, a handful at field capacity gives only a few drops. Growers wet substrate to field capacity before spawning it, because substrate that's too wet colonizes slowly. More on field capacity →
Flow hood: A flow hood (laminar flow hood) blows HEPA-filtered air across a work surface in a smooth stream, so spores and bacteria in the room are carried away from open plates, jars and bags. It's the step up from a still air box for agar work and transfers.
Flush: A flush is one wave of mushrooms that a block, bag or bed produces at about the same time, followed by a rest before the next wave. Most indoor blocks give two or three flushes, and each later flush is usually smaller than the one before. More on flush →
Fresh air exchange (FAE): Fresh air exchange (FAE) is swapping the CO2-rich air around fruiting mushrooms for outside air, through filtered holes, hand fanning or an exhaust fan. It keeps CO2 low enough, usually under about 1,000 ppm, for blocks to pin and grow normal caps. More on fresh air exchange (FAE) →

G

Grain spawn: Grain spawn is sterilized cereal grain, such as rye, millet, wheat or sorghum, fully colonized by mushroom mycelium. Growers mix it into bulk substrate to start a block, or use it to inoculate more grain. Each kernel is a separate point the mycelium grows out from. More on grain spawn →

H

Hyphae: Hyphae are the thread-like cells a fungus grows as. A mass of hyphae is mycelium, and a mushroom is built from tightly packed hyphae too.

I

Incubation: Incubation is the stage after inoculation when sealed jars, bags or blocks sit somewhere warm and steady while mycelium colonizes the grain or substrate. It ends when the container is fully colonized and ready for its next step: spawning to bulk, or fruiting conditions. More on incubation →
Inoculation: Inoculation is putting living mushroom culture or spawn into a prepared substrate so its mycelium can colonize it. Growers inoculate sterilized grain from liquid culture or agar, bulk substrate from grain spawn, and logs from plug or sawdust spawn. More on inoculation →

L

Liquid culture: Liquid culture (LC) is live mushroom mycelium growing in a sterilized, nutrient-rich broth, usually water with a little malt extract or honey. Growers inject it through a self-healing port to inoculate sterilized grain, and test a drop on agar before trusting it. More on liquid culture →

M

Master's Mix: Master's Mix (also written Masters Mix) is a mushroom fruiting substrate of equal parts hardwood sawdust and soybean hulls, hydrated to about 60% water and pressure-sterilized in bags. It is the best-known supplemented sawdust, used for oyster, lion's mane, chestnut and other wood-loving gourmet mushrooms. More on Master's Mix →
Monotub: A monotub is a plastic storage tote with holes cut in its sides for air, used as a small fruiting chamber. Growers fill it with bulk substrate or set colonized blocks inside it. Our CO2 and fresh air guide gives a starting hole layout.
Mushroom spawn: Mushroom spawn is living mushroom mycelium grown on a carrier, usually grain, sawdust or wooden dowels, that growers use to seed a larger substrate. It works like seed: you mix it into straw or sawdust, or plug it into logs, and the mycelium grows out from every piece. More on mushroom spawn →
Mycelium: Mycelium is the body of a fungus: a mass of fine, thread-like filaments called hyphae that grows through a substrate and digests it. Growers raise it on grain and bulk substrate, and once it has fully colonized its food, the mycelium can produce mushrooms, its fruiting bodies. More on mycelium →

O

Overlay: Overlay is a thick, matted layer of mycelium on the surface of a substrate or casing that pins struggle to break through. Growers usually tie it to leaving a block too long in colonization conditions, with stale air and little evaporation.

P

Pinning: Pinning is the stage when a fully colonized mushroom block starts forming pins, the first tiny mushrooms. Growers trigger it by moving the block into fruiting conditions: fresh air, high humidity, some light and, for some species, a cooler room. More on pinning →
Primordia: Primordia (singular: primordium) are the earliest recognizable stage of a mushroom, the tiny knobs that grow into caps and stems. Growers call them pins. They grow from hyphal knots, small clumps of mycelium that are the first visible sign of fruiting. More on primordia →

R

Relative humidity (RH): Relative humidity (RH) is how much water vapor the air holds compared with the most it could hold at that temperature, as a percentage. Warm air holds more water, so the same air reads a lower RH when it warms up. Our humidifier guide covers fruiting targets.

S

Shotgun fruiting chamber (SGFC): A shotgun fruiting chamber is a clear plastic tote drilled all over with small holes and lined with damp perlite, which keeps the air humid while air moves through the holes. It's a cheap first chamber for a few small blocks; a Martha tent is the usual next step.
Side pinning: Side pinning is when mushrooms form along the sides of a tub or bag, between the substrate and the wall, instead of on the open surface. Light and air reaching gaps along the wall usually cause it; see why mushrooms pin on the sides.
Spawn to bulk: Spawn to bulk is the step where fully colonized spawn, usually grain, is broken up and mixed into a larger bulk substrate such as pasteurized straw or supplemented sawdust. The mycelium grows out from each piece of spawn until the block is colonized and ready to fruit. More on spawn to bulk →
Sterilization vs pasteurization: Sterilization vs pasteurization is the choice of how to clean a mushroom substrate before spawning it. Sterilization uses pressurized steam to try to kill every microbe, dormant spores included, and suits rich substrates like grain and supplemented sawdust. Pasteurization uses gentler heat or lime to kill most competitors, and suits low-nutrient substrates like straw. More on sterilization vs pasteurization →
Still air box: A still air box (SAB) is a clear plastic tote turned upside down, with two arm holes cut in one side, used for mushroom culture work. The air inside stays still, so fewer airborne spores drift onto open agar plates, grain jars or bags while you work. More on still air box →
Substrate: Substrate is the material mushroom mycelium grows through and feeds on before it fruits, such as straw, hardwood sawdust, logs, wood chips or coffee grounds. Growers pick a substrate to suit the species, wet it to the right moisture and usually pasteurize or sterilize it before adding spawn. More on substrate →

T

Trichoderma: Trichoderma is a genus of green molds, often called the most common contaminant in mushroom growing. It first grows as dense white mycelium that can pass for mushroom mycelium, then turns green as it makes spores, and it can strike grain, bulk substrate or fruiting blocks. More on trichoderma →

Growing a particular species? The grow guides give conditions and timing for each one.

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