Going From Colonized Spawn to Bulk Substrate

If you’re ready to take your mushroom growing to the next level, spawning to bulk substrate is a key step. This method allows your colonized spawn to spread through a nutrient-rich medium, setting it up for a strong fruiting stage later on.

What You'll Need:

  • Colonized grain spawn

  • Bulk substrate (I recommend my Master Mix or any mix of hardwood sawdust, soy hulls, or straw)

  • Myco bags

  • Disposable gloves

  • Spray bottle with isopropyl alcohol (for sanitizing)

Step 1: Prepare Your Workspace

Start by sanitizing your work area and tools. Clean any surfaces that will touch your materials with isopropyl alcohol. It’s crucial to keep everything as sterile as possible to avoid contamination. Wear disposable gloves and sanitize them regularly during the process.

Step 2: Hydrate the Wood Pellets

Place the dry wood pellets directly into the mycology bags. Use a ratio of 1:1.5 wood pellets to boiling water by weight (e.g., for 1 pound of wood pellets, add 1.5 pounds of boiling water). This ratio ensures the pellets are fully hydrated without becoming overly wet.

To calculate the correct amount of water:

  • Weigh the wood pellets you’ll be using.

  • Multiply the weight of the pellets by 1.5 to determine the amount of water to add.

Pour the boiling water over the pellets for pasteurization. Fold the bag over itself to help retain heat, and allow the pellets to hydrate fully as they cool. Let the bag sit overnight to cool completely before proceeding.

Step 3: Prepare the Spawn

Once the substrate has cooled, gently break up your colonized spawn inside its bag to ensure even distribution. The spawn should be broken into small, manageable chunks for easy mixing with the substrate.

Step 4: Mix the Spawn with the Hydrated Substrate

Add the broken-up spawn to the hydrated substrate in a ratio of approximately 1:2 to 1:4 (spawn to substrate), depending on your spawn amount and desired colonization speed. Using sanitized, gloved hands, thoroughly mix the spawn and substrate until evenly distributed.

Proper mixing is crucial for consistent colonization. Seal the bag to allow space for gas exchange, avoiding tight packing so the substrate remains loose to promote airflow

Step 6: Incubate the Substrate

Store the bag in a dark area at a stable temperature of 65-75°F, depending on the species. Over the next 1-3 weeks, the spawn will colonize the bulk substrate, forming a dense mat of white mycelium. Once colonization is complete, your substrate will be ready for the fruiting phase.

Tips for Success:

  • Field capacity: Ensure bulk substrate is moist, but not soaking wet—just a few drops when squeezed.

  • Break spawn evenly: Thoroughly break up colonized spawn before mixing.

  • Mix thoroughly: Ensure spawn is evenly distributed in the bulk substrate for even colonization.

  • Don’t overpack: Gently pack substrate in the grow container, leaving air pockets for good airflow.