If your mycelium is not growing—or worse, if it looks off—don’t worry. You’re not alone. A lot of beginners (and even experienced growers) run into problems during colonization. In this post, we’ll go over the most common reasons for mycelium not growing and how to fix it.
Your substrate needs to be properly hydrated. If it’s too dry, the mycelium will stall. If it’s too wet, it can suffocate or invite contamination. Aim for a field capacity where squeezing the substrate produces a few drops of water—but not a stream.
Fix:
Rehydrate dry substrate before inoculating. If it’s too wet, consider mixing in dry vermiculite to absorb excess moisture.
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 the 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.
If your grain or substrate wasn’t sterilized properly, contaminants like mold or bacteria may be competing with your mycelium—often winning.
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.
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.
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.
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.
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.
Growing mushrooms takes a bit of dialing in, but once you understand how to control your environment, results become consistent. If your mycelium is not growing, there’s almost always a fix—you just have to spot the issue early and correct it. We have your back throughout the process, and are always happy to help.
If your mycelium isn’t spreading in the jar or bag, it’s usually due to incorrect moisture levels, poor temperature control, or contamination. Make sure the substrate is properly hydrated, the temperature is in the ideal range, and there are no signs of mold or off smells.
You can sometimes save stalled or slow-growing mycelium if there’s no contamination present. Improving environmental conditions—such as adjusting temperature or gas exchange—can help it resume growth. If contamination is present, it’s best to discard the batch.
The best temperature for mycelium growth is typically between 70°F and 78°F (21°C to 25°C), depending on the species. Temperatures outside this range can slow colonization or promote contamination.
You can tell if your liquid culture is contaminated by looking for cloudiness, floating particles, strange coloration, or off smells. To be safe, always test your liquid culture on agar before using it for inoculation.
Mycelium typically takes 2 to 4 weeks to fully colonize a bag or jar. Under optimal conditions, you should see visible growth within 7 to 10 days after inoculation.
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