Mycelium is Not Growing? 7 Common Mistakes (and How to Fix Them)

If your mycelium isn’t growing or looks unusual, don’t panic. You’re definitely not alone. Many beginners, and even experienced growers, run into issues during colonization. In this post, we’ll cover the most common reasons mycelium may stop growing, why it can look abnormal, and what you can do to fix the problem.

1. Too Much or Too Little Moisture

Your substrate should be properly hydrated. If it’s too dry, the mycelium may stall. If it’s too wet, it can suffocate or become more prone to contamination. Aim for field capacity, where squeezing the substrate releases a few drops of water, not a steady stream.

Fix:
Rehydrate dry substrate before inoculating. If it’s too wet, consider mixing in dry vermiculite to absorb excess moisture.

2. Temperature Outside Ideal Range

Mycelium grows best in the 70–78°F (21–25°C) range for most species. Temps below 65°F will slow colonization dramatically, and temps above 80°F increase contamination risk. Maintaining proper temperature for mycelium is one of the most important parts of growing.

Fix:
Use a thermometer to monitor your space. Heat mats or a temperature-controlled grow tent can help stabilize conditions if needed.

3. Incomplete or Improper Sterilization

If your grain or substrate wasn’t properly sterilized, contaminants like mold or bacteria may start competing with your mycelium and often overtake it.

Fix:
Always sterilize using a pressure cooker or autoclave for the proper duration (e.g. 90–120 minutes at 15 PSI for grain). Avoid cutting corners here.

4. Weak or Contaminated Inoculant

Bad liquid culture or spore solution = bad results. Contamination may be invisible to the eye but will destroy your chances of success.

Fix:
Use high-quality liquid culture from a trusted supplier or test your LC on agar before using. Never reuse old or suspect syringes.

5. Not Enough Gas Exchange

If your container is fully sealed or lacks proper filter patches, CO2 will build up and stall growth.

Fix:
Use jars or bags with micropore tape, filter lids, or built-in patches to allow for passive gas exchange while maintaining sterility.

6. Wrong Substrate for the Species

Different mushrooms prefer different substrates. For example, oysters love straw or hardwood, while psilocybes thrive in CVG or manure-based blends. If the wrong substrate is used, that could be why mycelium is not growing.

Fix:
Double-check your species requirements. Make sure your substrate aligns with what your mushroom strain actually wants to grow on.

7. Patience (Mycelium is Not Growing Yet)

It’s easy to assume something is wrong when things look slow, but mycelium doesn’t always grow visibly every day.

Fix:
Leave your jars or bags alone for at least 5–7 days after inoculation before checking. Avoid shaking or handling them too much.

Final Thoughts

Growing mushrooms takes a little dialing in, but once you understand how to control your environment, your results become much more consistent. If your mycelium is not growing, there is almost always a fix. The key is learning how to spot problems early and make the right adjustments. We are here to support you throughout the process and are always happy to help.