When you read or talk about growing mushrooms, three or four parameters came up like temperature, humidity, and CO2 level. May be light. But they say you don’t need that much light. That’s all, but is it really?
In today’s article, I want to address the 12 important growing factors I am aware of today. These growing parameters can be grouped together as extrinsic and intrinsic factors.
An extrinsic factor in the context of growing mushrooms is something that will impact the growth of the fruiting body primarily.
An intrinsic factor in this context is something that will impact the growth of the mycelium, the primordia formation, as well as the fruitbody development.
And here comes the kicker. Only if all 12 factors or parameters depending on what you will call them are in the optimal range, the mushroom growth will be optimal.
With that said, there is no parameter better than the other. You need all of them lined up if you want to cultivate mushrooms successfully.
Let’s get started.
The 6 extrinsic factors
The importance of the cultivation temperature
One of the first parameters which you want to control is the temperature in the growing room (Fig. 1). As it could be daunting having for each of the mushroom species its own fruiting chamber (even it would be optimal) they get grouped together.
If I did that, I would come up with the following ranges:
Group 1 (cold): 10 to 16 °C (50 to 61 °F)
Group 2 (warm): 17 to 23 °C (63 to 73 °F)
Group 3 (hot): 24 to 30 °C (75 to 86 °F)
Keep in mind that these ranges are not fixed. I just come up with them. Placing your mushrooms into one group or the other should only depend on the optimal temperature for that species.
Figure 1: Temperature range of various mushroom species for the fruiting phase
Which means each mushroom species has its own optimal range (Fig. 1). If the temperature is below this range, then it can happen that, for example, no pinhead formation is taken place. Or the fruitbody development takes longer, which can increase the risk of contamination.
Dealing with the temperature can be a challenge, especially if you are living in a warm or hot climate zone.
To help you with that, I wrote an article in which I am talking about 14 strategies to keep your fruiting chamber cool in hot climate and as a follow up a more in-depth one on the topic How to control climate in greenhouses with an earth air heat exchanger.
Feel free to check both articles out.
The influence of the grow room humidity
The second factor I want to address is humidity. As mushrooms contain up to 90 % water, we have to provide enough moisture to avoid damaging the fungi.
This is due to the transpiration of the mushroom itself. It could be found that the highest growth occurred with the lowest transpiration, which is achieved at the highest humidity.
In figure 2, I listed some humidity values which I found in Paul Stamets’s book.
Again, I would group them together like so.
Group 1: 70 to 75 % RH
Group 2: 80 to 85 % RH
Group 3: 90 to 95 % RH
Figure 2: Humidity range of various mushroom species for the fruiting phase
If you want to learn more about How to handle temperature and humidity the right way, feel free to follow the link to my article. In it, I address the importance of the design of your grow room and especially the position of your humidifier.
The importance of the CO2 Level
The third factor is the CO2 level. The amount of CO2 in the air determines the amount of aerobic growth of the mushrooms. This is especially true during fruiting body development (Fig. 3). Therefore, the CO2 level is dropped from usually 2,000 – 5,000 ppm to below 2,000 ppm.
As mushrooms are releasing CO2 during the growth, it is crucial to remove the excess as a high concentration will lead to a deformation of the fruiting body.
During the fruiting phase, we can again group the mushrooms together.
Group 1: < 500 ppm
Group 2: < 1,000 ppm
Group 3: > 1,000 ppm and < 5,000 ppm
Figure 3: CO2 range of various mushroom species during the fruiting phase
Therefore, separating the mushrooms according to the CO2 level (Fig. 3), especially group 3 form the rest, can avoid crop loss.
The overlooked factor light
While the first three parameters are the obvious ones, the fourth parameter is often neglected. You, therefore, read-only something on the line “If you can read a newspaper, then you have enough light.”
As this might be true, I think we are ignoring an important factor. What do I mean by that? When the cultivation of mushrooms started out, people tried to mimic nature. And as mushrooms are found more in shaded places, they assumed that light isn’t that important.
But you don’t grow your mushroom in the forest. You want to cultivate them indoors. As nature has to adapt itself to the available conditions, it doesn’t mean that the conditions are optimal. This means you, as an indoor mushroom grower, can give the mushrooms what they needed.
As far as I understand, it seems that most mushrooms can handle light in a much broader sense than we thought.
If you want to learn more about this topic, I recommend first the article on Do mushrooms need light? followed by How light will impact your mushroom yield.
In the first article, I will distinguish between mushroom species that do not need light at all and mushroom species that need the transition between darkness and brightness to form fruitbodies.
In the second article, I talk about the influence of light quality on the growth of mycelium and fruitbody development.
The necessity of the proper air exchange
Via the next and fifth factor, air exchange, many of the just described factors can be influenced.
On the one side, a proper air exchange helps the mushroom literally to breathe. The fungus transpires, as we learned during the last sections. The air adjusts the humidity level as well as the CO2 level around the mushroom.
On the other side, the temperature inside the grow room can be reduced by increasing the air exchange rate and, therefore, maintain the discussed optimal range.
The right treatment of the substrate
The final and sixth extrinsic factor is the treatment of the substrate, also known as sterilization.
This step is on the one side needed to keep the contamination level low and, therefore, the competition for your mushroom mycelium.
On the other hand, it starts to breakdown the cell walls of your substrate so that the mycelium can easier access it. But at the same time, the components cellulose, hemicellulose, and lignin are also available for the competitors.
How much this breakdown occurs depends on the sterilization method of your choice. It is, therefore, your job to balance between enough reduction of the competitors and the amount of breakdown of the substrate itself.
If you want to learn more about this topic, I summarized a lot of information into an article on How sterilization will impact your mushroom yield. Starting with the basics, I go into great detail about each component that will affect the growth.
The 6 intrinsic factors
The suitable nutrient mix of the substrate
The first intrinsic factor nutrient is an obvious one. As you start your mushroom farming career, you learn about it in the first class you take. In these classes, most will talk about the macro-nutrients carbon and nitrogen and especially the C/N-ratio.
That was true for me as well. But over time, the more I read and analyzed the data, I start wondering if we are missing something. While the C/N-ratio is a good indicator, the carbon and nitrogen source are, in my opinion, way more important.
And this brings me to the compound’s cellulose, hemicellulose, and lignin itself and especially the ratio between them.
If you feed your mushroom, which loves cellulose with lignin, it will not grow as fast and big as it could. I know all agro-substrates contain a certain amount of all of the three, but I am talking about the optimum level of them.
Paying attention to the ratio of cellulose, hemicellulose, and lignin in respect to the mushroom species you want to grow will improve your yield.
If you are new to this topic, you can find more information in my articles How substrate influences your mushroom yield and 6 reasons why you should use supplements. In these articles, I will address the importance of the ratio I just talked as well as the parameters supplements will impact (and it’s not only the yield).
The influence of the particle size
You are reading, right. The particle size of your substrate has an impact on the growth of your mushroom. A topic not many people are aware of or talking about.
An excellent way to illustrate my point is to compare the growth and especially the yield of Shiitake (Lentinula edodes) grown on a log or on sawdust.
If you use logs to grow Shiitake, then you see the first growth in year two, which yields at around 0.23 lbs. If you used sawdust, instead, you would get the early growth after 80 days with a yield of around 1 lb. More about this comparison can be found in my three-part series Part 1, Part 2 and Part 3.
How is that possible?
Think in terms of density. If you inoculate a log, the mycelium has to grow through a high-density material. In comparison is the density of sawdust very low. The mycelium can, therefore, grow faster.
Second, because of the slow growth, the majority of the energy which the mycelium produces will be spent on digestion and not on growing fruiting bodies. The mycelium is kind of exhausted.
In my article How substrate influences your mushroom yield, I address the influence of the particle size more in detail an showing you the problem if you are buying sawdust from mills.
The proper substrate moisture
Besides the humidity, it is important to have the right amount of substrate moisture. Or to say it differently: “Without the right amount of moisture, the mushroom doesn’t grow.“
If we have too much moisture in the substrate, the mycelium has difficulty to breathe, which leads to a suppression of the fruiting body formation. If the moisture level is too low, it will also lead to the death of the fruiting body as fewer nutrients will be delivered to it.
The importance of the pH value
The pH level of your substrate has a direct influence on the growth rate on the number of fruiting bodies as well as on the yield of your mushrooms. This means for all of the three values, there is a strong correlation between pH level and result.
Therefore, all mushroom growers are adding, for example, lime to the substrate to balance the pH level to around 7.
If you are, for example, growing Oyster mushrooms (Pleurotus spp.) and use too much of it and you are ending up in the alkaline regime (pH 8), then the growth will be suppressed which will then lead in lower yield. On the other side, a more acidic level (pH 6) won’t affect the growth that much.
But keep in mind if you are using, for example, lime to sterilize your substrate, you have to use more of it in order to reduce the amount of contamination, and as some of them are fungi, you know now why your mushroom won’t grow in this environment.
The less known factor electrical conductivity
The next and fifth factor, electrical conductivity, is an interesting one. I didn’t find much about this factor to write more on that. But I didn’t want not mentioning it just because I don’t have the answer yet, either.
This mainly because I found some hints about this topic during my research on morels. In one of the papers I was reading, I discovered that morels grow in areas with high electrical conductivity (Fig. 4).
Figure 4: Electrical conductivity of the soil (orange) underneath morels and away from them (blue)
If this is the case, I am pondering, then this could be another growth factor for mushrooms in general. But that’s something for later. I will add more to this paragraph on the way. So, it makes sense to come back to it from time to time.
The importance of oxygen
The last and final factor is oxygen. As mushrooms need oxygen to grow, the amount inside the substrate plays an important role.
There are at least two factors that influence the amount of oxygen. The first one is the particle size and the second one, the moisture content of the substrate.
As the size of the substrate particle defines the gap between each other, the gap itself determines the amount of air exchange between the mycelium and the outside world. If the particle size is too small, the aeration will be limited, and the growth of the mycelium slows down.
This limitation can also be happening if the moisture content of the substrate is too high.
Some of these growth factors are obvious, and some don’t. Knowing them and especially reflecting on them will increase over time, not only your understanding, but it will help you to grow more successfully.
Let me know in the comment section below what kind of growth factors you pay the most attention to and why?
Thanks for sharing.
 Own figure based on Stamets 1983
 Own figure based on Stamets 1983
 Mandal 2019
 Own figure based on Stamets 1983
 Bellettini 2019
 Singh 2014