Glossary of Common Mushroom Growing Terminology: A Beginner’s Guide

Growing mushrooms at home is a great way to get an ongoing supply of nutritious fresh mushrooms, and you don’t need a lot of expensive equipment to get started.

But you’ll need a little knowledge, and although there are excellent mushroom growing books and online courses available, they contain terminology that beginners often find confusing.

Common Mushroom Growing Terminology

Below is a glossary of common mushroom-growing terminology to help you make sense of the information you gather.


The shortened name given to mushrooms that have stopped growing or aborted. 

Aborts can be different sizes but are usually small mushroom pins that stop growing due to incorrect fruiting conditions or sudden drastic changes in temperature and humidity levels.


An organic jelly-like substance extracted from the cell walls of red algae.

Mushroom growers use a mixture of water, agar and nutrient-rich substances, like malt extract, to create sterile agar plates to grow and store contaminant-free mushroom cultures.


A perennial plant in the legume family that people cultivate worldwide for livestock feed. 

Also called lucerne, it’s known for its high vitamin, mineral and protein content and is used as a cover crop or green manure and for grazing, hay and silage. 

Oyster mushroom growers often add alfalfa hay to straw substrates to provide additional nitrogen, proteins and lipids for the mycelium.


A machine used for steam sterilization that works similarly to a pressure cooker but is much larger. 

When closed, autoclaves form sealed chambers that use pressurized steam to reach and maintain high temperatures that kill viruses, bacteria, fungi and spores.

Mushroom growers use autoclaves to sterilize bulk substrates.

Biological Efficiency (BE)

A measurement that growers use to calculate the performance of different mushroom strains on specific substrates. 

To calculate biological efficiency, you divide the weight of fresh mushrooms harvested, from all flushes, by the dry substrate weight.

Blocks (Substrate)

A word used to describe bags or containers of a bulk mushroom growing substrate.

Once the mushroom mycelium has grown throughout the bulk substrate and it’s fully colonized and ready to fruit, it’s known as a fruiting block. 


The topmost part of a fruiting body or mushroom that gives the mushroom its distinctive shape and contains and protects spore-producing gills, pores or teeth.

Carbon Dioxide

A colorless, non-flammable gas exhaled by mushrooms and humans. 

A carbon dioxide molecule contains one carbon atom and two oxygen atoms and is represented by the symbol (CO2).

Casing Layer

Moist, water-retentive material, such as coco coir, vermiculite or peat, that mushroom growers place on top of a fully colonized substrate before initiating fruiting.

The casing layer helps with moisture retention and creates a consistently humid environment for mushroom pins that encourages growth and reduces the number of aborts.

Clean Room

An enclosed space with a controlled environment and minimal airborne pollutants like dust, pollen, fungal spores and other microbes.

It could be anything from a clean bathroom with closed windows and low contamination levels to a specially designed room with fans and filters to remove airborne particles. 


The process of mushroom mycelium growing and spreading throughout a substrate. 

During colonization, the mycelium grows and obtains the nutrients it needs to fruit, but it won’t produce mushrooms until the substrate is fully colonized and environmental conditions are right.


Unwanted, harmful organisms, like mold or bacteria, that grow in mushroom cultures and substrates and compete for nutrients.

Contaminants often spread very quickly and inhibit or destroy mushroom mycelium.


This word has two meanings when referring to mushroom growing:

  1. Cultivated mushrooms that farmers grow on a large scale and harvest for subsistence or profit; For example, mushrooms are a high-value crop as you can grow them quickly in small spaces. 

  2. The mushroom yield you get from your fruiting block; A crop of mushrooms is also called a flush of mushrooms, and you usually harvest more than one crop or flush from a fruiting block.


Living mycelium of carefully selected mushroom species or strains growing in a nutritious medium. 

Mushroom cultures usually come in a petri dish, syringe or test tube, and growers use them to inoculate substrates and produce mushroom spawn.


An electrical device with a heating element, fans and vents that circulate heated air to remove moisture from fruit, vegetables and mushrooms.

Mushroom growers use dehydrators to dry mushrooms to preserve them for later use or to make mushroom powder.

Flow Hood (Laminar Flow Hood)

An enclosed workstation or box with a HEPA filter that mycologists use to create a contaminant-free environment.

Mushroom cultivators use laminar flow hoods when working with agar plates and mushroom cultures and also for inoculating sterilized substrates.

A laminar flow hood works by drawing air into the HEPA filter, where 99.97% of particles are removed and then blowing a consistent, laminar flow of clean air toward the user, preventing contamination.


A term used for a batch or crop of mushrooms produced from a mushroom substrate or fruiting block. 

Once a flush or crop of mushrooms is harvested, there is a resting period, and then the mycelium produces another flush.

You’ll generally get 2 to 3 flushes of mushrooms from a block of substrate.


The last phase of the mushroom growing process, during which mushrooms or fruiting bodies begin to emerge from the colonized substrate.

Fruiting Body

The fleshy, above-ground part of a fungus that most people know and recognize as mushrooms. The purpose of a fruiting body is to produce and distribute spores so the fungus can reproduce.

Fruiting Chamber

An enclosed space with controlled conditions that mushroom growers use to mimic the natural conditions required for fungi to thrive and produce mushrooms.

Fruiting chambers range in size and can be made using plastic totes, mini-greenhouses, grow tents, shipping containers or entire rooms.


Thin, paper-like structures layered side by side, often on the underside of a mushroom’s cap, that produce and disperse spores. 

Gills have distinct colors and features that mycologists use to help identify mushroom species.


A sealed, easy-to-clean box with two holes on the side containing permanently attached gloves that allow you to reach and work inside the box without introducing contaminants. 

Green Mold

A common, fast-growing contaminant that frequently grows in mushroom substrates. 

Also known as Trichoderma, green mold enjoys temperatures between 77 and 86°F (25 and 30°C) and ranges in color from pale green to dark emerald green.


A naturally occurring mineral found worldwide that mushroom growers use to supplement mushroom substrates.

Gypsum, also known as calcium sulfate hydrate, comes as a fine powder and provides mycelium with extra minerals and trace elements.

Adding gypsum to a substrate is believed to encourage faster colonization and the production of more mushrooms with larger cap sizes.


The gathering, cutting or collecting of a mushroom crop for consumption or preservation.

The word harvest can also be used to refer to the total crop of mushrooms that are collected.

Our beginner’s guide to harvesting mushrooms has more information on when and how to harvest mushrooms.

HEPA Filter

A high-efficiency air filter that can remove 99.97% of airborne contaminants, including mold, dust, pollen, spores and bacteria.

Mushroom growers use HEPA (high-efficiency particulate air) filters to build laminar flow hoods that reduce contamination when working with mushroom cultures and inoculating substrates.


A measure of the amount of water vapor in the air. Humidity is measured in different ways, but mushroom growers use relative humidity that’s shown as a percentage.

Relative humidity compares the actual amount of water vapor in the air to the maximum amount the air can hold at its current temperature.

The same amount of water vapor will cause higher relative humidity in cold air than in hot air.

Many mushrooms need relative humidity levels of 90% and above to thrive.

Hydrated Lime

Powdered calcium hydroxide Ca(OH)2 that’s low in magnesium and high in calcium. 

Mushroom growers use hydrated lime in casing mixes and to increase the pH of water when pasteurizing substrates using the cold water lime bath method.


An instrument used to measure the amount of water vapor in the air.

Mushroom growers often use a hygrometer to monitor the relative humidity levels in fruiting chambers. 


Long thin thread-like structures that fungi use to grow through a substrate and absorb nutrients.

Hyphae group together and form large, intricate networks called mycelium. 


The period after inoculation during which mushroom mycelium grows and colonizes a substrate.

Incubation Chamber

Any insulated space, for example, a closet, room or basement, where you can maintain optimal incubation temperatures using minimal energy.


Adding mushroom culture or spawn to a prepared substrate. 

Inoculation may involve inserting spawn plugs into holes drilled in logs, adding mushroom culture to agar plates or grain in a sterile environment or mixing spawn into a bulk substrate.

Isopropyl Alcohol

A colorless, flammable liquid (C3H8O) used to kill microorganisms and clean containers, surfaces and hands when working in sterile environments.


A building or room that provides controlled conditions and equipment for scientific research, experiments and tests.

Laboratories are also often used for the manufacture of chemicals and medicines. 

Lime Bath

A solution of hydrated lime and water with a pH between 11 and 13 that mushroom cultivators use to pasteurize organic material for growing mushrooms.

Cold water lime bath pasteurization is generally used for less nutritious substrates like straw and sugarcane bagasse.

Liquid Culture

A nutritious solution of water and specific sugars that contains living mushroom mycelium. 

Mushroom growers use liquid culture to grow, store and swap mycelium and to inoculate agar plates and other substrates.

Martha Fruiting Chamber

A small to medium-sized mushroom fruiting chamber with shelves and a clear plastic zip-up cover for easy access.

Originally adapted from a Martha Stewart hanging closet, hence the name, most growers now create DIY Martha fruiting chambers using mini indoor greenhouses. 

Masters Mix

A mushroom substrate blend made from a 50:50 mix of hardwood sawdust and soybean hulls.

Mushroom growers credit T.R. Davis of Earth Angel Mushrooms for inventing Master’s Mix, as he was the first person to run trials using this substrate mix.

His trials showed that a 50:50 mix provided the best yield possible without increasing the risk of contamination and deformation.

Medicinal Mushrooms

Mushrooms containing numerous bioactive compounds, micronutrients and proteins that people use in powdered or extract form to help prevent, alleviate and heal diseases

Our complete guide to medicinal mushrooms has more information for you.


The main body and longest-living part of a fungus, usually hidden underground or in rotting logs, stumps or substrate blocks.

Mushroom mycelium is made up of thousands of delicate, thread-like hyphae that join together to form a complex network of fibers that grow through organic matter in search of nutrients.


The study of all organisms in kingdom fungi, including rusts, smuts, yeasts, molds, mildews and mushrooms. 

Mycology is considered a branch of biology, and it explores the biochemical and genetic properties of fungi, their relationships with other organisms and their role in ecosystems and human lives.


A word used to describe fungi that form mutually beneficial relationships or associations, called mycorrhiza, with plants and trees.

Mycorrhizal mushroom mycelium interacts with the roots of plants, extending their root system and helping them access more nutrients. In return, the fungi obtain simple sugars.


A chemical element found in the form of a colorless, odorless, tasteless gas that exists in large quantities in air and can combine with most other elements.

Oxygen is necessary for all life forms to survive, and fungi, like humans, breathe in oxygen and exhale carbon dioxide.


A process used to reduce the number of harmful competitor organisms in a mushroom substrate before inoculating it with mushroom spawn.

There are several different pasteurization methods, but some of the most popular are hot water pasteurization and cold water lime bath pasteurization.


A lightweight, white, porous, granular material made from expanded volcanic glass that mushroom growers often use in small fruiting chambers to help maintain humidity levels.

Perlite is sterile, has a neutral pH and holds a lot of water, making it ideal for use in shotgun fruiting chambers.

pH Level

A measurement that indicates how acidic or alkaline a substance or solution is. pH is measured on a scale of 0 to 14, with 7 being neutral. 

If the ph Level of a substance is less than 7, it’s acidic, and if it’s higher than 7, it’s alkaline.


A word used to describe organisms that use sunlight and carbon dioxide to produce organic compounds for food.

Phototrophic is also used to describe organisms, including fungi that grow towards or away from light.


Tiny baby mushrooms in the first stages of growth are called mushroom pins, as they often resemble pinheads. 

When mushroom mycelium shifts its focus away from growing and begins to form tiny fruiting bodies or pins, the process is commonly called pinning.

Popcorning (Specific For Shiitake)

The final stage of colonization for shiitake mushrooms, during which the mycelium turns brown and forms round, bulging bumps or knots on the surface of the substrate.

Pressure Cooker

A sealed cooking pot that traps steam and increases pressure to create high temperatures. 

Mushroom growers use pressure cookers to sterilize small batches of a substrate.


A naturally occurring compound produced by several species of mushrooms.

When ingested, the human body converts psilocybin to psilocin which has psychoactive properties that affect the senses and emotions and can cause hallucinations. 


A word used to describe fungi that produce root-like structures called rhizomorphs.

Rhizomorphs are complex rope-like mycelial structures made of a dense mass of parallel hyphae that the fungi use to absorb and transport nutrients. 


A word used to describe organisms, including saprotrophic fungi, that feed on dead and decaying plant material.


Dust and small particles of wood created during woodworking activities, including sawing, sanding, planing, and routing.

Mushroom growers use untreated hardwood sawdust, a by-product of the timber and furniture industry, to create sawdust substrate blocks to grow wood-loving mushroom species.

Shotgun Fruiting Chamber

An easy-to-build, low-maintenance mushroom fruiting chamber made from a clear plastic tote with holes on all six sides and a layer of damp perlite at the bottom.

Soybean Hulls

An agricultural by-product of soybean oil production, soybean hulls are the outer coat or skin of a soybean that’s removed during processing.

Mushroom growers use these nutritious, fibrous hulls to supplement mushroom substrate mixes, and they’re an important part of the Master’s mix blend.


A colonized carrier material, usually grain or sawdust, that holds a specific strain of mushroom mycelium and is used to transfer the mycelium to another substrate.

Spawn Run

Another term used to describe the stage after inoculation during which mushroom mycelium colonizes a substrate. Also, see Incubation.


The name given to the process of adding and mixing mushroom spawn into a growing medium. Also, see Inoculation.


Microscopic reproductive cells that contain the genetic material necessary to grow a new fungus and perform the same function for fungi that seeds do for plants.

Mushrooms release millions of spores from their spore-bearing surfaces that get dispersed by wind, water, insects or animals.

Spore Print

A unique pattern on a foil, paper or glass surface made by mushroom spores falling from a mature mushroom cap that’s left undisturbed for several hours.

Spore prints are used for mushroom identification, cultivation and art.


The part of the mushroom that supports the cap and elevates it above the substrate. 

Also known as the stipe or stalk, the stem raises the gills high enough for the mushroom to effectively release its spores for wind or animal dispersal. 


A method of preparing substrates using steam, time, temperature and pressure to kill all living organisms and spores in the substrate.

To sterilize a substrate, you’ll need temperatures of 250°F (121°C) or higher for at least 2 hours.


A specific variety of mushrooms within a species that, although similar genetically, have different characteristics.

Commercial mushroom strains are selected for desirable characteristics, including yield, consistency, colonization rate and fruiting body shape, color or size.


The dry grass stalks left after drying and threshing cereal crops to remove the seeds.

Growers commonly use wheat, oat, rye, barley and rice straw as substrates for growing oyster mushrooms.


Any organic material that provides mushroom mycelium with the nutrients and moisture needed to grow and produce mushrooms.

Mushrooms will grow on a range of substrates including, sawdust, straw, coffee grounds, cardboard, coco coir and even books.


Adding nitrogen and carbohydrate-rich supplements to mushroom substrates for faster mycelial growth and improved yields.


A measure of the warmth or coolness in a place, substance, object or body relative to a standard numerical scale and measured with a thermometer.

Ideal temperatures for mushroom growth vary by species, with some mushrooms tolerating a broader range of temperatures than others.


A fast-growing cellulolytic filamentous fungus that often contaminates mushroom substrates. 

Trichoderma or green mold is commonly found in substrates during the spawn run or incubation phase, where it outgrows the mycelium and consumes large amounts of nutrients.

But it can also occur during fruiting if the humidity levels and airflow are not correct and causes severe crop losses. 


The strong-smelling, edible fruiting body of a mycorrhizal fungus. Unlike other mushrooms, truffles are produced underground and look like rough, lumpy potatoes.

They’re highly sought after by chefs and some of the most expensive mushrooms in the world, as they’re hard to find and challenging to cultivate.


The amount of fresh mushrooms you get from a block or container of substrate calculated using the total weight of all the mushroom flushes produced before the substrate is depleted.

Discover our top 10 tips for new mushroom growers.

Final Thoughts

We hope this glossary helps you in your quest to grow mushrooms.

To learn more about growing mushrooms, visit our Mushroom Growing Hub or try our introductory mushroom cultivation course.

You’ll soon be enjoying delicious, homegrown gourmet mushrooms.