Slow Mycelium Growth

Growing mushrooms takes a lot of patience, but sometimes we can’t help but wonder, isn’t this going a little too slow? Suppose you suspect that your mycelium is growing slower than it should. In that case, there are a couple of things you can do to ensure you’re creating an environment conducive to growth, such as using a different growth medium or an incubator or even tweaking the amount of moisture present.

How Fast Should Mycelium Grow?

Numerous factors affect whether the mycelium will grow and at what speed. For example, the type of mushroom strain, the type of substrate used, and the density of the substrate will all have an effect.

Similar to growing mushroom fruitbodies, growing mushroom mycelium requires different incubation times for different mushroom species. As a result, mushroom mycelium takes anywhere between two weeks and two months to grow.

We’ve written before about the first signs of mycelium growth and how you can best distinguish it from mold. 

What Factors Affect Mycelium Growth?

Like many other things, growing mushrooms is a skill that needs to be practiced and perfected. Fortunately, there are a few common factors that affect mycelium growth that you can tweak to your advantage.


Creating the right environment for the specific species of mushroom you are growing is the most significant factor affecting mycelium growth. For example, trying to grow a mushroom that’s more suited to colder temperatures during warm weather is setting yourself up for failure.

Air Exchange

Although mushrooms don’t require as much fresh air as humans, not having an adequate amount of fresh air will affect growth. Without proper air exchange, the carbon dioxide levels will build up too much and stunt growth.


Mycelium needs a moist environment to grow and produce fruiting bodies. As mushrooms consist mostly of water, dried out, the mycelium will not produce any fruiting bodies. Therefore, the right humidity is also crucial to ensuring the mycelium can maintain the perfect level of moisture.

On the other hand, too much moisture will also negatively affect growth. This is because it will lead to a soggy substrate and standing water that creates the ideal circumstances for mold and bacterial growth.

The Right Spawn

Spawn is the colonized carrier that holds a specific strain of mushroom mycelium until it is ready to transfer to another substrate. The spawn is already in the substrate if you have a growing kit.

Always buy spawn from a reputable company and ideally one that’s not too far away. The longer the spawn must be transported, the greater the chance that the quality might be affected.

Once you receive the spawn, use it immediately. The quality also deteriorates the longer it sits around. The quality of the spawn will have a direct effect on your mycelium and eventual mushrooms.


Light is a bit less important for mycelium growth than for the fruiting process, but it’s good to include this factor here.

Mushrooms don’t require light in the same way as plants do, given they don’t generate their food from photosynthesis.

However, many mushroom growers recommend some light once the fruiting process starts. A good rule of thumb is enough light so that you can comfortably read a book in the space where you are growing your mushrooms.

How Do You Encourage Mycelium Growth?

You can do a couple of things to ensure your mycelium has the best chance of growing. But, again, a word of caution – always do research about the specific mushroom you are trying to grow. Just as you would treat each houseplant slightly differently based on its unique requirements, so does each mushroom species have differing needs.

Use An Incubator

Mycelium has a sweet spot at which it grows optimally depending on the type of species. But higher temperatures don’t necessarily mean better growth. Too high temperatures can even kill mycelium and encourage the development of contaminants. This is because mycelium also generates heat as it grows.

On the flip side, growth is slowed down when it’s too cold. So only use an incubator if the average temperature in the room is 72°F or 22°C.

Take note of the different temperature requirements to promote mycelium growth vs. the fruiting process. For example, certain mushrooms, such as the king oyster mushroom, prefer to fruit in cooler temperatures and might even struggle in temperatures over 70°F or 21°C.

Choose The Right Growth Medium

Choosing the right growth medium for the species of mushroom you are growing is a critical element for success. While your mycelium might survive in a less-than-ideal substrate, it will not only inhibit mycelium growth but can also contribute to bacterial growth.

Sterilize Your Growth Medium

Some mushrooms require that the growth medium is sterilized to prevent and kill off any bacterial growth. This is done by placing log chip material or straw in large steamers. Bacteria is the main threat to mushroom growing.

Choose The Right Location

The spot where you place your mushrooms can be one of the most significant factors in determining the speed of mycelium growth. Some species may need very moist conditions for the mycelium to thrive, whereas others need full shade. Try moving your mycelium to a different spot to see if that makes a difference.

Protect The Mycelium Against Wildlife And Insects

Wildlife and insects can quickly destroy all the hard work you’ve put into growing mushrooms. In addition, the mycelium’s structure is extremely delicate, so any rooting animals can disturb or even destroy the structure.

Even if mycelium just gets disturbed, it may become infected and die. Fruiting mushrooms also attract all kinds of predators and insects. Put up a fence to keep these animals out.


This may sound like a silly tip, but arming yourself with as much knowledge as possible will help you make small changes in the environment to optimize growth. In addition, spending some time reading advice from others can save you a lot of time and effort and make the whole process more enjoyable overall.

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