Getting Started: The Colonization Stage

Arguably the most difficult part of mushroom cultivation is the “colonization stage” which includes the preparation of the colonization medium, the sterilization of the colonization medium, the inoculation of the colonization medium with mushroom genetics, and the colonization of the spawn. There are several tasks that one must perform during these steps, paying close attention to detail and sterility, as there are several avenues for potential user error that may result in contamination. This guide aims to provide a clear and concise explanation of this tricky stage so that the home/hobby mushroom cultivator can refer to it should he/she have any questions.

STEP 1 - Preparing the colonization medium

For this step, you will require the following materials:

  • Rye grain berries (or another colonization medium)

  • A large bowl

  • A colander

  • A tray/tub/tote

  • A fan (optional but recommended)

First, select your colonization medium. Here at Spores Lab, we have experimented with several colonization mediums but we have had the best results using rye grain berries. Other colonization mediums that you could use include but are not limited to white wheat, corn, oats, millet, and birdseed, though note that using any of these mediums will typically result in less overall yield of mushroom compared to rye grain berries. Whichever colonization medium you decide to use, ensure that the medium is organic and that it has NOT had a fungicide applied.

Organic, non-fungicide rye grain berries.

Once you have your rye grain berries, place however much grain you will require (keeping in mind that the grain will expand in volume once it is hydrated), in the large bowl and fill the bowl with cold water (tap water is fine). Pour out the water and repeat this several times until the water is pouring noticeably clearer. Now fill the bowl with cold water and cover the grain. The water level should be 6-8 inches above the grain because the water level will drop as the grain absorbs the water. Allow the grain to soak for 18-24 hours (the amount of time is dependent on the humidity of your environment - if you live in a dry environment, soak for 24 hours, if you live in a humid environment, soak for closer to 18 hours).

When you return to your grain, the water level will have dropped significantly. This is normal and simply means your grain was able to absorb the moisture.

Pour out any remaining water in the bowl and then fill the bowl with HOT water (NOT BOILING WATER - JUST TAP WATER AT MAXIMUM HEAT), and let the grain sit in the hot water for 15 minutes. This heat differential allows the grain to fully “plump” and absorb the maximum amount of moisture possible. After 15 minutes, pour out the hot water, strain the grain using a colander, and wait until the colander stops dripping.

Now spread the grain out evenly in the tray/tub/tote and place it in a high-airflow area for about 1 hour to dry the exterior of the grain. If you have a fan, you could use it to dry the grain more efficiently.

Grain being dried by a fan on a drying rack.

Ideally you want the grain to be as saturated as possible, but with little moisture on the exterior surface of the grains (the industry term for this level of saturation is “field capacity”). A rough rule of thumb that you can use to estimate the correct dryness of your grain is to pick up a small handful of grain and then turn your hand upside down. If a few grains stick to your hand, your grain is at the correct dryness. If no grains stick to your hand, the grain is probably too dry, and if too many grains stick to your hand, the grain is probably still too wet.

A handful of grain at field capacity.

Step 2 - Sterilizing the colonization medium

For this step you will require the following materials: