Glossary

The words you will meet on tek pages and grower forums, defined plainly and sourced where a source exists.

Growing basics

Spawn: Mycelium of a known species grown on a carrier such as grain, sawdust or wooden plugs, generally isolated in a sterile lab so it is free of other organisms. It is what you add to a substrate to start a grow¹. See Grain spawn in jars.
Substrate: Any material that feeds the mushroom mycelium: logs, wood chips, straw, sawdust, coffee grounds, grain hulls and other carbon-rich materials¹.
Inoculation: Bringing spawn into contact with the substrate to start growth, whether by drilling and plugging a log or mixing spawn into a bag¹.
Mycelium: The thread-like body of the fungus that grows through the substrate. The mushroom is its fruiting body.
Leap off: The moment mycelium first grows from the spawn onto the new substrate, typically around four days after inoculation¹.
Colonisation (spawn run): The period after inoculation when mycelium grows through the substrate. When it has grown through all the available food, the substrate is fully colonised and ready to fruit¹. Log growers call the same stage the spawn run².
Through-spawning: Mixing spawn all the way through a substrate instead of leaving it on top. It shortens the spawn run¹. See Grain spawn in bags.
Initiation: The step between mycelial growth and mushroom formation, usually triggered by cooler temperatures and more oxygen, a cold or water shock, or cutting holes in the bag¹.
Pins (primordia): The first tiny mushrooms. Humidity matters most during the first four days after initiation, while they are forming¹.
Flush: A group of mushrooms that fruit within a short period after a single forcing event². Bags and logs give several flushes.
Forcing (shocking): Triggering fruiting on purpose. Shiitake logs are soaked in cold water for 12 to 24 hours²; shiitake blocks can be soaked for 5 to 12 hours or chilled for 12 to 24¹. See Logs with plug spawn.
Bolt: A log inoculated with spawn². See Logs with plug spawn.
Popcorning and browning: The bumpy texture and brown skin a shiitake block develops after full colonisation. Cornell waits until about 75% of the block has browned before fruiting it¹. See Supplemented sawdust blocks.

Conditions and preparation

Fruiting conditions: The temperature, humidity, fresh air and light that mushrooms need to form. Cornell’s targets: low 60s °F for most species, humidity above 85% during pinning and around 80% after, CO2 below 1000 ppm (800 for oysters), and enough light to read by¹. See Martha tent.
Fresh air exchange: Replacing the air around fruiting mushrooms so CO2 does not build up. High CO2 gives oysters long stems and small caps¹. See Shotgun fruiting chamber.
Field capacity: A substrate holding as much water as it can without free water draining out of it. Growers check it by squeezing a handful: a few drops is right, a stream is too wet. As one worked example, GroCycle hydrates master’s mix to about 60% moisture³. See Supplemented sawdust blocks.
Pasteurisation: Reducing competitors in a low-nutrient substrate without killing everything, for example holding straw at 140–160 °F for about two hours¹. See Pasteurised straw (hot water).
Sterilisation: Killing everything in a rich substrate with pressurised steam, as for agar, grain and supplemented sawdust¹. UF/IFAS uses 15 psi for about 30 minutes for agar and grain⁴. See Grain spawn in jars.
Lime treatment: Soaking straw in water made highly alkaline (pH 12–13) with low-magnesium hydrated lime, which kills most competitors without heat¹. See Cold-water lime pasteurisation.
Supplement: A nitrogen-rich addition such as wheat bran or soybean hulls mixed into sawdust to raise yields; it makes the substrate need full sterilisation¹. See Supplemented sawdust blocks.
Biological efficiency: Fresh mushroom weight as a percentage of dry substrate weight, used to compare substrates. The SARE lime trial reported average biological efficiencies by treatment, for example 41% for lime and 29% for heat⁵.

Cultures and kit

Agar: A nutrient gel in petri plates, used to store a strain or clone a mushroom from tissue. Very easy to contaminate¹. See Agar.
Liquid culture: Mycelium grown in a nutrient broth. Fast and easy to inoculate with, but prone to degenerating after repeated subculturing⁶. See Liquid culture.
Still air box: A clear tote with arm holes that keeps air still during transfers. UF/IFAS suggests one for home growers⁴. See Still air box vs flow hood.
Laminar flow hood: A fan pushing air through a HEPA filter to create a clean working area⁴¹. See Still air box vs flow hood.
Filter-patch bag: A heat-tolerant plastic bag with a breathable patch, used for spawn and substrate in 5 and 10 lb sizes¹. See Grain spawn in bags.
Master’s mix: A 50/50 blend of hardwood sawdust and soybean hulls, credited to T.R. Davis of Earth Angel Mushrooms³. See Supplemented sawdust blocks.

Contamination names

Trichoderma (green mould): A common contaminant identified by rapid greenish growth⁷. Penn State describes it as dense white mycelium followed by extensive green sporulation⁸.
Cobweb mould: Caused by Cladobotryum (also called Dactylium): a cotton-like mycelium, usually white, over the surface and the mushrooms. Its spores move with water and air, and it germinates fast at 95–100% humidity⁹.
Bacterial blotch: Pale yellow to brown lesions caused by Pseudomonas bacteria, likely where mushroom caps stay wet for four to six hours or more¹⁰.
Bacterial contamination (sour grain): Bacteria growing in wet grain or plates. UF/IFAS checks plates for bacteria and unwanted fungi and discards any contaminated ones⁴. See Grain spawn in jars.
Blue, green, black or yellow spots: UF/IFAS tells growers to look for these colours on bags as signs of unwanted fungi or bacteria⁷.

Sources

Methods of Commercial Mushroom Cultivation in the Northeastern United States. Willie Crosby (Fungi Ally) and Steve Gabriel, Cornell Small Farms Program, 2019 (Northeast SARE). Extension publication, checked 26 October 2026.
Best Management Practices for Log-Based Shiitake Cultivation in the Northeastern United States. University of Vermont Extension and Cornell University, 2013. Extension publication, checked 26 October 2026.
What Is Master’s Mix?. Adam Sayner, GroCycle (a grower-education site that also sells supplies). Grower guide, checked 26 October 2026.
Isolation of Mother Cultures and Preparation of Spawn for Oyster Mushroom Cultivation. Liao, Hsu, Hameed and Cotter, UF/IFAS Extension (EDIS SS663). Extension publication, checked 26 October 2026.
Alternative growing practices for oyster mushroom cultivation in the Northeast (FNE15-825). Willie Crosby, Fungi Ally, Northeast SARE farmer grant final report. Farm trial report, checked 26 October 2026.
Problems associated with the liquid cultivation of shiitake, Lentinula edodes (dissertation). Merja Itävaara, VTT Technical Research Centre of Finland, 1993. Research, checked 26 October 2026.
D.I.Y. FunGuide: Grow Your Own Oyster Mushrooms at Home. Hameed, Cotter, Liao and Hsu, UF/IFAS Extension (EDIS SS662). Extension publication, checked 26 October 2026.
Green Mold of Mushrooms. Beyer, Wuest and Anderson, Penn State Extension. Extension publication, checked 26 October 2026.
Basic IPM Practices for Organic Mushroom Farms: Fungal Diseases of Mushrooms. Gorgo-Gourovitch, Beyer and Pecchia, Penn State Extension, 2021. Extension publication, checked 26 October 2026.
Bacterial Blotch Disease. David M. Beyer, Penn State Extension. Extension publication, checked 26 October 2026.