Fruiting your spawn to bulk substrate doesn’t have to be hard. Although there are many bulk substrate recipes online, this preparation method is simple, straightforward, uses widely available ingredients, and does not require pasteurization.

This substrate prep is based on the BucketTek method, which is not true pasteurization.

Although this recipe works for the non-nutrient containing ingredients (Coir and Vermiculite) we will be using, when using additional ingredients such as worm castings or manure, you will want to do a full pasteurization.

Easy Bulk Substrate Preparation Instructions


  • 1 Brick (8 quarts) of 100% Natural Coco Coir.
  • 2 Quarts of Vermiculite
  • 1 cup of Gypsum – This ingredient is optional but provides calcium and sulfur, which is needed for healthy mycelium growth and also acts as a pH buffer.
  • 5 Gallon Bucket with Lid – Find this at Home Improvement Stores
  • 4 Quarts (one gallon) of Boiling Water. Tap water is fine, filtered water is better.

Step 1: Place the coco coir into a five gallon bucket. When using compressed coir bricks it is important to break up the brick into small pieces.

Step 2: Add vermiculite to the 5 gallon bucket.

Step 3: Place a large pot on the stove and add 4 quarts of water. Turn the burner to high and add gypsum to the water. Bring the water to a boil.

Step 4: Turn off the heat and stir the gypsum/water mix using a large spoon, then pour the hot water over the ingredients in the five gallon bucket.

Step 5: Place the lid on the bucket and allow to sit for 10 minutes. Once 10 minutes is up, remove the lid and stir up all of the ingredients using a large spoon. Be careful, the substrate will be very hot.

Step 6: Place the lid back on the bucket and allow the substrate to cool overnight (4-6 hrs).

Step 7: Use it!

Have you had success with this recipe, do you have a variation? If so, we would love to hear from you. Leave a comment in the box below!


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