A common question of beginners is, “how long does it take to colonize a bag fully?” Instead of giving you just a list with some mushroom species and the time, I will provide you a detailed description of several factors that are influencing the growth of the mycelium.
As the saying goes:
“Give a man a fish, and you feed him for a day; teach a man to fish, and you feed him for a lifetime“
I will, therefore, talk briefly about
- Spawn rate
- Particle size
- Sterilization method
Table of Contents
To get a first impression about the growth rate, we just look up some numbers in Paul Stamets’s book Growing Gourmet and Medicinal Mushrooms. To have easier access to these and other parameters, I extracted and put them into a spreadsheet (Table 1).
In the column “Spawn run,” you will find the short answer to your question. As you can see, some of the species only need 12 days to fully colonize a bag while others take up to 45 days. But this is only valid for one species for one specific substrate.
Table 1: Overview of different growing conditions for various mushroom species
If you choose a different one, species, or substrate, then you will end up with a different growth rate. To illustrate the effect of the substrate on the growth rate, I put some data from a research paper into a graph (Figure 1). I really like this graph because it shows the impact of the different substrates on the growth of different species.
If we take, for example, Pleurotus ostreatus, a common mushroom species, and a good one for beginners to start with, then this graph indicates that the mycelium growth rate is about 6 to 7 mm per day.
If you want to grow instead of Pleurotus pulmonarius, the mycelium growth rate drops down to 5 to 6 mm per day. This means while even both mushrooms are part of the same genus, they behave differently.
Figure 1: Mycelium growth rate vs substrate type
If you want to figure out the best strain, you should take a look into my article, “What is the Best Mushroom Strain.” In this article, I describe a method with which you can compare different species with each other.
Mushroom growers are using a typical spawn rate of about 5%. But I also saw some of them using as little as 1%. The impact of the spawn rate on time to full colonization is evident. The more we spawn we use, the shorter it should take.
The following diagram (figure 2) shows the duration until the pinhead formation. While in the beginning, we see only a small decrease in time, at the 6% mark, we see a sharp drop. This underlines our assumption.
But as we continue to increase the spawn rate, the time starts to rise again. The reason for that is two-fold. First, a high spawn rate leads to an increase in temperature throughout the colonization. If it gets too hot inside the bag (> 25°C), the heat will kill our mycelium. Second, the more spawn we are using, the more likely it is that the mycelium runs into itself and, therefore, they slow down because there is not enough food.
Figure 2: Influence of the spawn rate on the pinhead formation (days)
If you want to learn more about inoculation, then my in-depth article “How your Inoculation Method can Impact your Mushroom Yield” is a good start. You will be surprised in which ways your spawn rate will vary.
As we already saw in figure 1, the type of substrate matters a lot. But why is this the case? To understand this, we take a look at different wood types and especially at the composition of them. To do so, we examine a study done in 2014. In this study, the author used sawdust from five different trees and a mixture of all five to grow Pleurotus ostreatus.
The author measured the mycelium running rate, the yield, and the BE. The five trees were Fig tree (T2 Ficus carica), Raintree (T3 Albizia saman), Mahogany tree (T4 Swietenia mahagoni), Ipil ipil tree (T5 Leucaena leucocephala) and Eucalyptus tree (T6 Eucalyptus globulus). T1 is a mixture of all five sawdust. Each substrate was supplemented with 30% wheat bran and 1% lime.
The results of this test can be seen in figure 3. In this graph, the mycelium running rate (MRR) is given in cm per day and vary between 0.52 cm/day and 0.70 cm/day.
Figure 3: Effect of the wood type on the mycelium running rate (MRR)
Let’s look at another substrate (figure 4). In this figure, the MRR is given in days. As shown, sugarcane bagasse has the slowest MRR and wheat straw, the highest MRR (figure 4).
Figure 4: MRR for five different types of substrate.
Both figures are indicating in the direction we have to investigate further. If we follow this path, we found that our substrates contain different compounds, especially cellulose, hemicellulose, and lignin (Table 2).
Table 2: Chemical composition of softwoods and hardwoods, temperate-zone hardwoods (values in %)
As you know, there are three different types of wood-decay fungus, and each of them reacts differently to these compounds (Table 2).
- The brown rot fungi
They break down hemicellulose and cellulose that form the wood structure.
- The soft rot fungi
They break down cellulose in the wood.
- The white-rot fungi
They break down the lignin in wood.
Most of the edible mushrooms like Pleurotus (“Oyster” mushroom), Lentunila (“Shiitake”) and Agaricus (“Button” mushroom) are white-rot fungi.
If you want to learn more about mushrooms in general, I wrote this article, “What are mushrooms?”
If we now look at the correlation between the three compounds and the mycelium running rate, we found that hemicellulose and cellulose have a negative while lignin has a positive correlation (figure 5). Which means in the end that too much hemicellulose and cellulose reduces the growth rate and lignin supports it.
Figure 5: Correlation between the chemical components (hemicellulose, cellulose, and lignin) and the MRR [cm/day] for Pleurotus ostreatus and Pleurotus florida
Because there might be confusion between MRR in days and MRR in cm/days, I put both correlations next to each other (Figure 6). The top figure shows the MRR measured in cm per day, and it shows that the higher the amount of hemicellulose, the slower the MRR. The bottom figure shows the MRR measured in days and shows the higher the amount of hemicellulose the longer it takes, which makes sense because the MRR in cm per day is smaller.
Figure 6: Correlation between hemicellulose and MRR with MRR [cm/day] (top), MRR [days] (bottom)
Now to understand these results better, let’s compare these substrates more in detail. If we do that, it gets interesting. We talked already about the influence of hemicellulose, cellulose, and lignin on the mycelium running rate. To see this effect in action, we will first look at the chemical composition of these five substrates (Figure 7 to Figure 9).
Figure 7: Hemicellulose content of different types of straw
Figure 8: Cellulose content of different types of straw
Figure 9: Lignin content of different types of straw
The amount of hemicellulose and cellulose for sugarcane bagasse is one of the highest, which is terrible when it comes to MRR. While the lignin content is a little bit lower in comparison to wheat straw.
If we look at sorghum straw, we found a high amount of hemicellulose, low cellulose, and a high amount of lignin. But the MRR is one of the lowest (figure 4).
In the end, it appears that the main driver for MRR is hemicellulose.
For more information about the influence of substrate, I wrote an in-depth article “How your Substrate Influences your Mushroom Yield.” This article addresses all aspects of the topic substrate. What it should consist of, how to prepare and way more.
When it comes to supplementing your substrate, you can influence the composition of these three compounds and, therefore, the MRR. You will, although, influence the C:N ratio of your substrate.
To illustrate this, we will take a look at another research paper. Here the author used different nitrogen-rich supplements. The results showed that 21 out of 24 mixtures had a faster spawn run in comparison with the reference (Figure 10: corn cobs, green arrow). The other three were almost similar.
Figure 10: Influence of different nitrogen-rich supplements during cultivation of Pleurotus florida on corn cob substrate on the spawn run – CC: Corn cobs, U: Urea, AS: Ammonium sulphate, GF: Gram flour, SM: Soybean meal, MC: Mustard cake, GNC: Groundnut cake, CSC: Cottonseed cake, M: Molasses
After you found your perfect substrate composition and sterilized it (see the last chapter), you have to think about if you want to mix or not mix after you inoculated your substrate with spawn. I saw both variations, and both have their advantages and disadvantages. If we only look at the time to colonize, mixing is the way to go. But on the other hand. If you have to mix every single bag, you have to spend some time to do it. And don’t forget: “Your time is valuable!“
To illustrate the difference in time, let’s make a short calculation. We use a standard bag size of 10cm x 30cm x 8cm. The bag is filled 3/4.
If we only top spawn, then the mycelium has to grow through 22cm of the substrate (30cm x 3/4). At a growth rate of 6 to 7 mm/day, it will take roughly 31-37 days to colonize the bag entirely.
If you mix the time to full colonization is faster. How fast depends on how thoroughly you mix your bags. Assuming that the time for the spawn run in figure 1 is after mixing, then your bags should be fully colonized after 12 to 21 days. If we are using a more conservative estimation, we would compare our findings to 21 days. Top spawning would, therefore, take 16 days or 43% longer.
But as I said, you have to spend time doing the mixing. And, as I said earlier: “Your time is valuable!“
To illustrate the impact of the particle size, let’s look at a study which was done in 2001. In this study, the author ordered wood chips from different commercial hardwood sawmills. The requirement was that the wood chips should be between 4-0.21mm.
After analyzing the particle size, the author found the following distribution (Figure 11). As clearly visible, the variation between the four sawmills and, therefore, the provided particle sizes are large. Even though all the commercial sawmills used the SIEVE standard.
Figure 11: Particle size distribution of wood chip from four different commercial hardwood sawmills
Now, how does the particle size influence the growth rate? First, the smaller the particle size, the larger the surface area. Which provides the mycelium good growing conditions. But on the other side, small particle size increased the density of the bulk and, therefore, reduces the growth rate. Second, larger particles are increasing the aeration inside the block, but if the particle size is too large, the cap in between them is too large for the mycelium to overcome. The growth slows down.
A good particle size is between 0.85mm and 1.7mm.
In my article “How your Sterilization Method will Impact your Mushroom Yield,” I describe almost all aspects of sterilization more in detail.
Two factors that will impact the growth rate are, for example, the temperature and duration of the sterilization process. These two variables will impact the number of bacteria and competitive fungi within your substrate.
If the temperature is to low or the duration too short, your substrate will likely get mold. If you run the process too long, you are risking that your substrate starts to decompose. Depending on which mushrooms you want to cultivate, the beginning of decomposing will impact the growth rate of your fungus.
If you are still with me, I want to thank you. Because many before and after you won’t put in the effort to understand the details of mushroom cultivation. And that is fine, as long as it works for them and they are happy. But if you not only know what you are doing but you also understand why it is working, you will be ahead of your colleagues.
these details helps you to make changes on your farm to improve it and make,
therefore, more money. If something goes hay day, you know how already how to
fix it because you know already the possible causes.
 Own figure
 Own figure
 Own figure
 Own figure
 Own figure