Grain Spawn for Mushroom Cultivation

Pink Oyster Mushroom Grain Spawn
  • Colonized Pink Oyster Grain Spawn [left]
  • Millet Grain Spawn [right]

Purpose of Grain Spawn

Growing mycelium in grain spawn is an essential phase of the mushroom growth cycle. The primary purpose is to increase the mass of the mycelium, so it is healthy enough to fight off any airborne contaminates. The fungi will colonize the grain spawn as it consumes the vital nutrients. Young mycelium is susceptible to bacteria, mold, and other spores, so grain spawn is pressure sterilized to prevent contamination. Transparent vessels such as mason jars or myco bags offer the ideal environment to observe mycelium while its colonizes the grain. A laminar flow hood or still-air-box (SAB) is needed to reduce the risk of contamination when inoculating the grain with your chosen fungi.

Mushroom Grain Spawn

Types of Grain Spawn

Selecting a grain usually comes down to availability and price. Some like wild bird seed (WBS) are found at a local grocery or big box store. Feed-stores like tractor supply carry other grains such as oats or rye berries.

  • Pop Corn
  • Oats
  • Barley
  • And More

The size of the grain plays a factor for colonization speed. The smaller grains have more inoculation points allowing the grain spawn to mix more evenly throughout a substrate.

Preparing Grains Spawn

Most grain spawn requires a similar set of preparation steps, but there are some nuances for certain varieties. Some require additional steps while cleaning the grain; others may greatly increase in volume when hydrated, and so on. Thoroughly research the grain you plan to use to avoid unwelcome surprises. Below are the rudimentary steps needed to prepare your mushroom grain spawn.

  1. Clean/Rinse: Clean the grains and remove any debris.
  2. Additives: Mix in any desired additives such as coffee and gypsum. optional
  3. Hydrate: Hydrate the grains for 12+ hours (overnight).
  4. Cook: Cooking the grain until the water comes to a simmer.
  5. Dry: Strain the grain and allow the outer surface to dry off.
  6. Jars/Bags: Fill mason jars or myco bags with the hydrated grain.
  7. Sterilize: Kill off contaminates by pressure sterilizing the grains for 90 minutes at 15-PSI.
  8. Cool: Allow the grain spawn to cool before inoculation.

Grain Spawn Walkthroughs

  • Wild Bird Seed - Grain Spawn
    Wild Bird Seed

    Step-by-step instructions for preparing wild bird seed as mushroom grain spawn.

    Wild Bird Seed
Mycelium Colonizing Grain Spawn

Incubating Grain Spawn

Keep inoculated grain spawn in a warm and dark area. The particular species determines the exact temperature range for storing the grain spawn. Most species grow best around 70-80°F.

Light is often confusing for anyone new to cultivation. Fungi do not create energy through photosynthesis like plants. Instead, light acts as a signal to fungi, telling it which direction to fruit. There is some anecdotal evidence that mycelium grows faster with light, but I can't say that for certain.


If any of your incubating grain spawn show signs of contamination, remove it from the other immediately. It's unlikely the contamination will spread to the other jars/bags, but it's best to eliminate all factors.

What to do With Colonized Grain Spawn

Once the grain spawn is fully colonized you are able to use it in a number of ways.

Bulk Substrate

Mix the colonized grain spawn with the bulk substrate your fungi prefers to begin the next stage of the grow cycle.

Grain to Grain

Quickly increase the grain spawn quantity by inoculating fresh jars/bags with the colonized grain. To prevent contamination, conduct the grain transfer in front of a laminar flow hood or within a still-air-box (SAB).

Grain to Agar

Place a single colonized grain on an agar plate to grow out mycelium. Again, to prevent contamination, conduct the grain to agar transfer in front of a laminar flow hood or within a still-air-box (SAB).

Store for Later

Store the colonized grain in a refrigerated environment to use at a later date.