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Why Do My Mushrooms Have a Fuzzy Stem?

Fuzzy Mushrooms Stems
Updated on 07/24/21

Alright, so you’re growing your own gourmet or medicinal mushrooms, and you notice they are starting to grow a fuzzy stem.


What is this white fuzzy stuff, what does it mean, is it good or bad, and how do we go about fixing it—if we need to at all?

A lot of questions, so let’s get to it!!

What Causes Fuzzy Mushroom Stems – The Culprit

Alright, so what is this fuzzy white stuff growing from the stems of our beautiful mushrooms, and what is causing it?

In a nutshell, this fuzziness is called “fuzzy feet” and is a result of the mushrooms not getting enough oxygen. Remember that mushrooms and mycelium inhale oxygen and exhale CO2—just like we humans!

This fuzziness is typically caused by two growing factors:

  1. Poor fresh air exchange
  2. High humidity

Now, if you spend any time researching or browsing online forums, you’ll likely find hundreds of people battling over which of these two things are the culprit.

But I am here to tell you they both play a role, and here is why!

They both starve our mushrooms of oxygen.

For clarity, let’s cover each factor.

1. Poor Fresh Air Exchange [FAE]

Alright, as we said above, mushrooms require oxygen to thrive and also exhale CO2.

An interesting characteristic of these two gasses is that CO2 is heavier than oxygen and sinks below it.

So if you have a growing environment with poor FAE (fresh air exchange) and give the CO2 no downward direction to escape, it will simply pile up and eventually suffocate your mushrooms.

Because this CO2 buildup begins from the ground and works up, the base of your mushrooms will be the first area struggling to breathe.

2. High Humidity

Wait, how can high humidity suffocate our mushrooms? Don’t mushrooms thrive in high humidity environments?

While this is true, there is a little detail about humidity that isn’t well known.

You see, in any defined amount of space—let’s say a monotub—there is a finite amount of room for gasses to fit. Things such as oxygen, C02, nitrogen, and even water vapor are all fighting for room.

Now because this space is finite, the more of one thing you put into this space, the less room you have for other things.

With this in mind, what happens with higher humidity?

To put it plainly, when we increase our humidity and add moisture, we are removing space for gasses like oxygen– thus, our mushrooms suffocate, and the fuzzy feet result.

We now understand why fuzzy mushroom stems occur, but what steps should we take in solving the problem?

How To Fix Fuzzy Stems and Why You Should Do It!

So what harm can fuzzy stems mean for your mushrooms?

Well, because fuzz stems occur from a lack of oxygen and fresh oxygen is need for your mushrooms to grow big and strong, the result of fuzzy feet is a smaller mushroom yield.

Considering that we spend a lot of time and patience cultivating these mushrooms, we may as well put in the extra effort to maximize our yield.

So how can we fix fuzzy feet?

The simplest way to fix fuzzy mushroom stems is to simply increase your fresh air exchange. The most common methods of doing this are manually exchanging air—such as fanning—or setting up an automated method such as a mushroom grow tent or even a monotub.

By doing this, you will not only increase the ratio of oxygen to CO2 but will also help decrease the humidity—2 birds, one stone.

Wrapping it Up!

I hope that this guide was helpful and has shown you that there is common ground in the never-ending debate of what causes fuzzy mushroom stems.

Remember that nature always tells you what it needs, and these fuzzy feet are nothing more than your mushrooms asking for some fresh air.