What is mushroom spawn?

Mushroom spawn sets the strain you grow and how clean the grow starts. Cornell's Small Farms Program defines spawn as "intentionally cultivated mycelium from a known species", isolated, usually in a sterile lab, so it is free of contaminants. Most growers buy it from a supplier, "much like a vegetable grower buying seed" (Cornell).

Spawn is a step after the culture. UF/IFAS Extension makes spawn by inoculating grain from a pure culture, then uses that "master spawn" to make more "planting spawn" for straw (UF/IFAS). See liquid culture and agar for the culture stage, and inoculation for the step itself.

Grain spawn is the usual choice for bags and straw, sawdust spawn for logs, and plug spawn for a few logs with simple tools.

Spawn	What it is	Best for
Grain spawn	Sterilized grain colonized by mycelium	Fast expansion and inoculating straw (Cornell); it "sticks to substrates like straw far better" (Fungi Perfecti)
Sawdust spawn	Colonized hardwood sawdust	Logs, with an inoculator tool; cheaper than plugs, and the mycelium moves into the log more quickly (Cornell)
Plug spawn	Colonized wooden dowels	Logs: "the only tool needed is a drill and hammer or mallet", but it costs slightly more per log and is slower to put in (Cornell)

Cornell's log guide is written for shiitake, and the UF/IFAS straw method for oysters.

How much mushroom spawn you need depends on the substrate. For logs, most growers estimate one 5-lb bag of spawn per 20–25 logs, 4–6 inches wide and 36 inches long (Cornell). For bags and straw, growers use a spawn rate, a percentage of the substrate's weight: UF/IFAS uses 5–10% on pasteurized straw (UF/IFAS). Our spawn to bulk page compares rates by substrate.

Store most mushroom spawn sealed in the fridge and use it soon. North Spore's help center gives grain spawn three months in a refrigerator, and sawdust and plug spawn six months to a year. Pink oyster can't be refrigerated and is best used within a month. Open a bag only when you're ready, since opening it early raises the risk of mold, and use it in one inoculation day (North Spore help center). UF/IFAS stores oyster spawn at 39°F (4°C), except tropical Pleurotus strains (UF/IFAS).

New spawn needs a short rest. Fungi Perfecti suggests at least 24 hours after arrival in case of shipping damage (Fungi Perfecti).

• Calling shaken spawn dead. Spawn broken up in transit looks uncolonized, but "each grain will still work as an inoculation point". North Spore suggests about 24 hours at room temperature to recover (North Spore help center).
• Putting pink oyster spawn in the fridge. See our pink oyster grain spawn guide and the pink oyster grow guide.

In Hypha, create each spawn bag as a transfer from its culture, and each block as a transfer from its spawn, so you can trace any block back to its source.