How long does it take for Mycelium to colonize a Jar?

An inoculated jar of substrate is usually colonized by mycelium in 3-6 weeks. Of course, this is a grave generalization. Time for complete colonization varies depending on circumstance. 

Factors that affect Speed of Colonization

Type of Inoculum

There are different types of inoculum such as grain spawn, liquid culture, and agar.

  • Mushroom Spawn is the quickest to colonize a jar. Takes about 4 weeks on average but can be as quick as 2.
  • Liquid Culture may take up to 8 weeks.
  • Agar is the slowest and can take more than 8+ weeks.
  • Spores can take a long time to colonize. Most often growers germinate spores on agar before spreading them onto spawn.

Quality of Inoculum

Inoculum is the living culture you use to inoculate your substrate. If the culture or spawn you are using is unhealthy, it will severely slow down the process. That is why you should always use fresh and vigorous culture for inoculations. Old cultures that have outgrown their substrate will no longer be as vigorous.

Attention: NEVER use contaminated or questionable inoculum. This will more often than not result in a wasted effort!

Growth Medium

Certain types of substrates colonize quicker. For example, straw is usually faster than sawdust. On the other hand, supplemented sawdust can colonize quickly! Typically, more nutritious substrates grow quicker but are more prone to contamination. How well you prepare the growth medium will also affect colonization speed. 

Problems with Growth Mediums that may affect colonization speed

  • Excessive or Insufficient Moisture
  • Heavily Compacted
  • Improperly Pasteurized/Sterilized
  • Low-Quality Substrate
  • The presence of softwood or other growth-inhibiting components
  • Contamination

Quantity of Inoculum

Using a higher percentage of inoculum may speed up the process. For example, using 10% instead of 5% mushroom spawn will have a change your results drastically. If you want your mushrooms to grow fast, consider using spawn rates up to 15%.

Mushroom Variety

Certain mushroom varieties such as oysters are quick and vigorous. Under the best circumstances, you can have a colonized jar in under 2 weeks. Others like shiitake are a bit slower and could take more than double the time.

Technique used for Inoculation

The entire inoculation process is a delicate matter. If conducted properly, colonization will occur smoothly. Improper technique results in slow colonization or complete failure.

Errors conducted during Inoculation that may slow down Growth

  • The substrate was still too hot during inoculation
  • Tools, jars, and other equipment was not properly sterilized
  • Spawn was insufficiently mixed into the substrate
  • Contamination caused by improper technique

Conditions during Incubation

Environmental conditions are extremely important during incubation. Inadequate temperatures and lack of air exchange are common issues during incubation.

Best Conditions for Incubation:

  • Choose a dark space
  • Mush mushrooms require temperatures between 65-75F. Try to keep it consistent and avoid temperature fluctuations. 
  • Have plenty of fresh air exchange. Excessive CO2 and lack of oxygen will slow down growth. Make sure your grow bag or growth vessel allows for air exchange. Do not incubate in a closed bin or bag!
  • Humidity should ideally be greater than 80%
  • Shake spawn every 1-2 weeks after inoculation to help distribute the growth.

What to do if your Mycelium is growing slowly

  1. Improve the incubation conditions. If everything else seems right, it may be a lack of fresh air exchange. 
  2. Wait patiently. Sometimes you think the culture is dead, but it eventually takes off!
  3. If you’ve waited more than 2 weeks and have not seen any mycelial growth it’s likely something didn’t go well. 
  4. Improve your methods and try it again! If you feel like you’ve done everything right, consider trying another provider of spawn.


Total Comments: ( 2 )

  1. I inoculated, six jars successfully and mycelium grew quickly after a week, but now it’s been three weeks and growth has slowed halfway to the bottom of the jars. Could this be due to CO2 accumulation in the jars? Can I open the jars to improve airflow? Add water?


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