Growing mushrooms is not an easy endeavor, but worthwhile. What do I mean by that? At first glance, growing mushrooms seems easy, and everybody can do it. This is true in theory and applies to all things in life. But if you look more closely, you will find more and more parts which have to come into play to get the highest quality for your customers.

I will address today in this article the basics of mushroom cultivation. Starting with the substrate and ending with contamination. I will guide you through these topics which will increase the likelihood that you will get the expected quality out of your production.

First, we will have a look at the substrate itself. We will discuss the pros and cons of each substrate for specific mushroom types.

Second, we will dive into the realm of sterilization and all the impacts it has on contamination and yield.

Third, we will analyze different growing conditions for certain mushrooms types to find the best growing conditions for your mushrooms.

Fourth, we will assess several locations and their impact on the yield.

Fifth, we will talk about different production techniques and tools to produce high-quality mushrooms.

Sixth, we will spend some time discussing waste management, and finally, in the seventh chapter, we will address the topic of contamination.  

Substrate

As you may know, mushrooms are growing on all sorts of substrates like straw, wood, or grass. But not all mushroom species will grow well on all these substrates. I experienced that while working on a mushroom farm in Canada.

The primary substrate there was wood. But the owner of the farm had no control over what type of wood he would get. Sometimes he would get for example beech but other times oak The mushrooms were growing, but with different yields. Unfortunately, the owner did not measure the yield of the various wood types in the past.

He just started while I was working alongside him on the farm. After realizing the difference and switching from wood chips to wood pellets, he increased his yield by 30% to 50%. That’s a lot, just by using the right substrate as a growing medium.

Another thing to know before we dig deeper into this topic is that mushrooms are classified into three different types.

• Primary decomposer
• Secondary decomposer
• Tertiary decomposer

Primary decomposer grows on all sorts of the substrate if it contains enough carbon. While secondary decomposer will only grow on a substrate that is already decomposed. And finally, the tertiary decomposer will grow only on the “leftovers” from the secondary decomposer.

For your mushroom production, you should use either primary decomposer like, e.g., oyster mushrooms or shiitake or secondary decomposer like, e.g., button mushrooms.

With that said, let’s dive in.

Most of the substrates which are used for growing mushrooms are a mixture of mainly three parts.

1. The main compound (e.g., wood or straw)
2. Supplements (e.g., wheat bran)
3. Water

When preparing the substrate, we must have several things in mind.

1. Mycelium running rate (MRR)
2. Numbers of days to initiation (NDTP)
3. Numbers of days to harvest (NDTH)
4. Biological & Economical Yield (BY & EY)
5. Biological Efficiency (BE)
6. The average length of stripe (ALS)
7. The average thickness of pileus (ATP)

Let’s talk about each of them.

The mycelium running rate (MRR) is defined by the distance (l) the mycelium grows within a certain amount of time (n).

The numbers of days to initiation (NDTP) is the time from stimulation to primordia initiation.

The number of days to harvest (NDTH) is the time from primordial initiation to harvesting the mushrooms.

The biological yield (BY) is defined as the yield per block without removing the lower hard and dirty portion.

While the economic yield (EY) is defined as the yield per block after removing the lower hard and dirty portion.

The biological efficiency (BE) is defined as the total biological weight in gram (TBW) to the total weight of substrate in gram used (TWS).

With 1 lb of fresh mushrooms grown from 1 lb of dry substrate as 100% biological efficiency.

If the substrate is moistened to approximately 75% water content and because most mushrooms have a 90% water content at harvest, 100% BE is also equivalent to growing 1 lb of fresh mushrooms for every 4 lb of moist substrate, a 25% conversion of wet substrate mass to fresh mushrooms of achieving a 10% conversion of dry substrate mass into dry mushrooms[1].

Now, after we have all these definitions in place, we can understand the differences between the different substrates better. Let’s have a quick look into typical types of substrates like straw and wood.

Substrate | Straw

Straw, as many of you already know, is a by-product of the agriculture industry. This means you as a future mushroom farmer will use the waste of one industry and turn it into a profit.

There are several types of straw-like rice straw, barley straw, or wheat straw. The main difference of them is their lignin, hemicellulose, and cellulose content, which impacts their C/N ratio. In other words, these three compounds are the nitrogen and carbon source for your mushrooms.

The amount of nitrogen and carbon, which is needed to grow mushrooms successfully depends on the mushrooms species you want to grow. While button mushrooms prefer a higher amount of nitrogen, the C/N ratio oyster mushrooms, on the other hand, prefer less nitrogen and more carbon.

This leads us to the first important number you must keep in mind while preparing your substrate – the C/N ratio.

The mentioned barley straw has a C/N ratio of 72 and is therefore considered a suitable substrate for growing oyster mushrooms. A little below that we have rice straw with a C/N ratio of 58. While wheat straw has a C/N ratio of 104.

But if we look at the different growing phases, for example of shiitake different C/N ratios are preferred. A ratio of 25 is considered an optimum for the mycelial growth, while a C/N ratio of 40 is better for the mushroom production phase.

Substrate | Wood

The types of wood are divided into softwood and hardwood. Examples for softwood are hemlocks, cedars or Douglas firs. Whereas oak, elm, chestnut or beech are classified as hardwood.

The density of wood has nothing to do with this classification. Although hardwood has, in general, a higher density than softwood.

This classification stems from the physical structure and makeup of the wood. Whereas softwood comes from gymnosperm trees which usually have needles and cones, hardwood comes from angiosperm trees that are not monocots.

There are three different ways to use wood as a substrate for growing mushrooms – logs, wood chips, and sawdust. Let’s make a side by side comparison of these three (Table 1).

	Log Cultivation	Wood chips	Sawdust
Pros	Cheap Easy	Good MRR Good yield & BE	Fast MRR Short NDTP Short NDTH High yield & BE
Cons	Labor intensive Low yield & BE Long NDTP Needs a lot of space	Can be labor intensive	Can be labor intensive

Table 1: Comparison between log, wood chips, and sawdust cultivation

After this short introduction, we will now look at the second component of a typical substrate mix the supplement part. To understand the effect of supplementation, we are looking at various levels of supplementation of wheat straw with rye bran as well as a mixture of wheat straw with other types of straw (Table 2).

More details about substrate and supplementation can be found in my in-depth article “How the substrate influences your mushroom yield –Substrate 201”.

Now, let’s dive in.

First, let’s have a look at the pure wheat straw itself. As shown in table 2, the time to harvest is with 37.5 days for wheat straw the shortest, but when it comes to yield and BE wheat straw underperforms by roughly 50-75%.

If we look at the performance of all supplementations, we notice that they all increase the growing time but also increase the yield, and BE.

And here comes the trade-off. You, as a mushroom farmer must think and calculate what is the optimum growing period in comparison to the received yield during the same time. Because the longer the growing time, the longer your capital is not working for you. Which in the end, means that you have costs, but no money is coming in. This loss has to be compensated by the higher yield.

Table 2: Effect of various agro-residues on growing periods, yield and biological efficiency of Pleurotus eryngii[2].

If you are interested in a more deep dive into the world of substrate just follow this link to my article on How Substrate Influences your Mushroom Yield

Sterilization

Before we can grow mushrooms on our substrate, the substrate itself has to be sterilized in one form or another. This process is needed to reduce the number of bacteria, viruses, and fungi, which are competing with your mushroom spores. Which means, sterilization give your mushrooms spores a heads up in colonizing the substrate first and therefore gives other species no chance to survive. This, however, does not necessarily mean that your spores will always win the race. Especially if you do not do a good job.

When it comes to sterilization, we distinguish between

• Pasteurization: Done at 60-80°C for up to 5 days at 0 Psi
• Super-Pasteurization: Done at 80-100°C for maximum of 15 hours at 0 Psi
• Sterilization: Done at ≥100°C for 1-2 hours at 15 Psi

As you already noticed, the sterilization process itself has three factors – temperature, time, and pressure. You may also see that the lower the temperature, the longer the process, or vice versa. And, the higher the pressure, the shorter the process.

On this note, I want to mention that the higher the temperature and the longer the process, the more you reduce bacteria and fungi. Which means the substrate is getting more sterile. But the longer and hotter you run the process, the more you start decomposing the substrate as well.

Which has an impact on the mushroom yield. Besides, the warmer and longer you run the process, the higher are your costs. In summary, higher costs combined with lower yield wouldn’t last you long.

We so far compared the sterilization processes by their temperature, time, and pressure. But we can also divide them accordingly to the methods.

• Composting
• Chemical sterilization
• Hot water immersion
• Steam sterilization (autoclave, pressureless)

Composting

Composting is typically used for growing button mushrooms (Agaricus), but it also found its way into growing oyster mushrooms (Pleurotus).

Composting is a two-step process:

• Phase 1, which is usually done outside, is a biological and chemical process and the first step to decompose the mixed raw materials. During this time this phase the substrate itself heats up to 80°C. 

Figure 1: Phase 1 – Piles of compost[3]

• Phase 2, which is done inside, is a biological process to finalize the decomposing. While in phase 1, the temperature is uncontrolled, in phase 2, the temperature is strictly controlled for a certain amount of time. In the first part of this phase – the pasteurization phase – the temperature is set to 56-60°C for 8 hours. After that, the temperature is dropped to 45°C for up to 7 days – the so-called conditioning period. The conditioning period ends after the volatile ammonium has been cleared form the process air.

Figure 2: Phase 2 – Look into a bunker[4]

Chemical sterilization

A big disclaimer: The shown information are just for education and information purpose only and should not be construed as advice. The provided information contains general information and may not reflect current legal developments or information. I do not make any representation or warranties concerning the accuracy, applicability, fitness, or completeness of the information. The information is not intended to substitute for professional advice. Please inform yourself by reading the instruction manual and material safety data sheet carefully, and ask a specialist before using any of these mentioned chemicals. I, therefore, disclaim any, and all liability to any party for any direct, indirect, implied, punitive, special, incidental or other consequential damages arising directly or indirectly from this information, which is provided as is, and without warranties.

Chemical sterilization is typically used because it is inexpensive. During my research, I found many scientific studies in which different chemicals are used to sterilize the substrate. Table 3 gives an overview of these chemicals and their classification accordingly to their risks.

Table 3: Overview of chemicals used in science papers for the sterilization of mushroom substrate

With that said, I do not recommend any of them, because the risks of using them for me are too high. They are to poison, toxic, or hazardous to handle.

Hot water immersion or scalding

Both methods are using 80°C warm water. The difference between the two of them is the duration. For scalding the substrate is typically immersed for 1 hour in hot water. For immersion, the duration is 1,5 hours.

Figure 3: Example of hot water immersion[5]

Autoclave sterilization

An autoclave is a big pressure cooker. By utilizing steam, a high-pressure environment is created inside the chamber. The higher the pressure, the higher the temperature of the steam can get. Typically parameters are 121°C and 15 Psi for 1-4 hours.

Figure 4: Example of an Autoclave[6]

Super-Pasteurization was first described by Paul Stamets in 1993 and described a method in which the substrate is pressure-less heated up to 88°C for 12+ hours.

Science paper #1

In a 2013 published science paper, the author compared to sterilization methods regarding their effectiveness to kill bacteria on the one side and the impact on the yield on the other side (Figure 5 and Figure 6).

For the thermal treatment, the substrate was steam pasteurized for 1 hour at 80°C. While for the chemical treatment calcium hydroxide (concentration 1kg/20kg in 100 liters) was used and the substrate immersed for 15 hours.

Figure 5: Total yield (kilogram) of Pleurotus ostreatus in different substrates sanitized with thermal method[7]

Figure 6: Total yield (kilogram) of Pleurotus ostreatus in different substrates sanitized with calcium hydroxide[8]

Table 4: Number of pests and diseases found in the substrates of Pleurotus ostreatus[9]

Table 5: Number of pests and diseases found in the Pleurotus ostreatus cultivation according to the sanitation method[10]

If you want to know How your Sterilization Method will Impact your Mushroom Yield just follow this link. It will bring you to my article in which I talk more in-depth about this topic.

Growing conditions

Growing conditions are a set of parameters under which the mushroom will grow. In general, these are corridors and not exact set points. In order to grow mushrooms, the conditions in the three phases must be set and under control. These phases are

• Spawn Run
• Primordia or Pinhead Forming
• Fruiting

During the spawn run, the mycelium colonizes the substrate. After initiation, the pinheads starts forming. If the conditions are still correct, the mushroom starts growing until he gets harvested. A good overview of these conditions can be found in Paul Stamets’s book the Mushroom Cultivator. I can absolutely recommend it to you.

To give you an idea of these parameters I extracted some of them from Paul Stamets book and put them into an excel file, so they are easily accessible, I insert below two screenshots (Table 6 and Table 7) of this file. As you can see, it contains not only the parameters of the three phases but also the expected number of crops per block and yield (BER) as well as the total duration of one cycle. In the last column, I rated each mushroom species accordingly to five specific parameters and got a number which I called Mushroom Value Rate (MVR).

This number tells me right away if I should grow a certain mushroom or not. For more information about this rating, check out my separate article about it.

Table 6: Overview of growing conditions for different mushrooms species for all three phases[11].

Table 7: Growing conditions for some mushroom species for the first phases[12].

One of the most critical parts of growing mushrooms is the initiation point. The initiation is usually down by dropping the current temperature by several degrees (Figure 7). After the pinhead is formed, the temperature is then raised again and hold constant until harvesting starts.

Figure 7: Temperature curve [°C] during the whole crop cycle[13].

The orange lines are indicating the transition from one phase to another. In this example, the temperature during the spawn run is set to 24°C and hold for 15 days. For the initiation, the temperature is dropped down to 13°C and hold for 5 days. After this time the temperature is then raised back to 18°C and hold until harvesting which takes place 6 days later. The total crop cycle (DTM) for this example is 25 days.

Besides controlling the temperature, the level of humidity and CO2 have to be under control (Figure 8 and Figure 9).

Figure 8: Example of the humidity level [%] during the whole crop cycle[14].

Figure 9: Example of the CO2 level [ppm] during the whole crop cycle[15].            

Speaking of the CO2 level. The level of CO2 measured in parts per million (ppm) has a significant effect on the NDTH, which is shown in Figure 10. As shown, the higher the CO2 concentration, the shorter the NDTH.

Figure 10: NDTH [days] vs CO2 concentration [ppm] [16]

The final things which must be under control are the airflow and the amount of light during the whole crop cycle (Figure 11 and Figure 12).

Figure 11: Example of the number of air changes [1/hr] during the total crop cycle[17].

Figure 12: Example of light intensity [lx] during the whole crop cycle[18].

Especially when it comes to light people usually tend to think the mushrooms do not need light to grow. But this is not the case at all. If there were not any light, the initiation would not occur, and therefore, no mushroom would start to grow.

To learn more about these parameters and how they affect the growth of the mushrooms, I wrote a detailed article.

Location

Your location where you want to cultivate mushrooms impacts them in several ways. The obvious once are temperature, humidity, and light. These three parameters can be controlled if you move from outdoor growing to indoor cultivation. But there is one more parameter which can only be changed if you move to another place; it is the altitude level.

During my research, I found a science paper that compared the same mushroom species but cultivated at different altitude levels (Figure 13).

Figure 13: Impact of the altitude on different growth parameters on Pleurotus ostreatus[19]

In this study, the first location (Peshawar) is at an altitude of about 200 meters (MASL) and the second location (Swat) at an altitude of about 1,000 meters. While the difference might not be vast, the impact on different growth parameters can be seen in figure 13.     

Production techniques and tools

In the following section, I want to give you a short overview of different production techniques and tools. Starting with the buildings. These can be simple like a bamboo house (Figure 14) or more sophisticated like an insulated greenhouse (Figure 15).

Figure 14: Example of a bamboo house in the Philippines[20]

Figure 15: Example of an insulated greenhouse[21]

The same goes for the interior. You can grow your mushroom in wooden fix beds (Figure 16) or in a more modern and fully automated fixed bed as seen in Figure 17.

Figure 16: Example of a wooden fixed bed used to grow button mushrooms[22]

Figure 17: Example of a modern fixed bed used for button mushroom cultivation[23]

Instead of fixed beds, you can also grow your mushrooms in columns as seen in Figure 18. Which is typically down on small scale mushroom farms.

Figure 18: Example of growing Pleurotus in substrate columns[24]

When it comes to growing mushrooms, we find two different growing techniques. In Western countries (the USA and Europe) mushrooms are typically grown either in fixed beds (Agaricus) or on blocks (e.g., Pleurotus).

While in Asian countries (e.g., China or Japan) mushrooms are typically grown in bags (e.g., Pleurotus see Figure 19) or bottles (e.g., Hypsizygus see Figure 20).

Figure 19: Example of bag cultivation of Pleurotus[25]

Figure 20: Example of bottle cultivation of Hypsizygus[26]

When it comes to irrigation, you just can use a water hose or a high-tech irrigation system, as shown in Figure 21.

Figure 21: Example of a modern irrigation system for growing button mushrooms[27]

Waste management

At one point or another while growing mushrooms, you will produce different types of waste. The primary source of your waste will be hopefully (at least after some experience) spent mushroom substrate or short SMS. But what is SMS exactly? After you harvested the last mushroom and decided that you do not want to use the substrate for another crop cycle, this substrate is called SMS.

Studies had shown that SMS is actually not a waste per se. In one specific study, they performed a meta-study on a spent substrate and found that it contains a lot of protein and fiber alongside with many minerals (Table 8).

Table 8: Characteristics of spent mushroom substrate (SMS) reported in different studies[28]

This high content of the SMS can be used for many purposes. One is the use of SMS as a nutrient source for plants (Table 9) or mushrooms (Table 10).

Table 9: Response of different plant species towards different doses and age of SMS[29]

The application of SMS as a nutrient source for mushrooms does not come unexpected, because as you remember, there are three types of mushrooms – primary, secondary, and tertiary decomposer. If your SMS was used for the cultivation of Pleurotus (primary decomposer), you could use it as a substrate to cultivate button mushrooms (secondary decomposer).

Table 10: Response of different mushrooms species towards different doses and age of SMS[30]

It can also be used in something called Bioremediation. Bioremediation is a process used to treat contaminated media by altering environmental conditions to stimulate the growth of microorganisms and degrade the target pollutants (Table 11).

Table 11: Additional advantages of using SMS in different types of soils[31]

If you are getting excited about this topic, I summarized a lot of information in my article Can you reuse spent mushroom substrate?

Contamination control

To sell mushrooms, you have to have continuous production of mushrooms. To achieve that you need a tight contamination control. In the next paragraphs, I will talk about different aspects of it.

In his book Growing Gourmet and Medicinal Mushrooms, Paul Stamets talks about six vectors of contamination.

• Cultivator
• Media
• Air (Mobil Contamination Unit, MCU)
• Water
• Inoculum
• Tools

The first and last vector is obvious but important to remember. As I wrote in my article about farm design to reduce the risk of contamination, all people are only allowed to move from clean areas to dirty areas and not the other way around. This means that when you start your day, you should start, for example, in the lab and end with harvesting.

People contribute between 30% and 40% to all contaminations in cleanrooms. We as humans release on average between 100,000 to 500,000 particles and germs per minute! Table 12 illustrates the level of particles with different activities.

Table 12: The Austin’s Contamination Index. Number of particles generated by person per minute, at different degrees of activity, wearing two different types of clothing (≥0.3mm)[32]

To get a better idea about the mentioned size of a particle (here ≥0.3 um) Figure 22 will give you some references. According to figure 23, a bacterium has a size of 1,000 nm or 1 um. Whereas a virus has a size of 100 nm or 0.1 um. If we compare these two sizes to the size of a mushroom spore which is about 10-12 um we will see a factor of 10-1000 between them. Therefore, if we want to avoid bacteria or viruses spreading, we need at least a filter system that stops everything below 10 um.

Figure 22: Size comparison[33]

Besides people, animals like ants, flies, mites, or cats, and dogs are helping to spread contamination. With that said, you as a farmer must make sure that you take measures against them. You can do this by using, for example, a fly screen for your doors and windows, and add fly strips in your rooms and check them frequently.

A good method of prevention is to use double doors and a small overpressure in between them. The overpressure suppresses the number of particles coming into the room.

But not only we have to wear some clothes (especially in the lab) we also must filter the incoming air. To illustrate what I mean, I got a diagram of the average value of fine dust over Germany (measured on the 01.01.2018). As you can see in figure 23, some cities overshot the level of 50 mg/m³ which is the maximum allowed level governed by law.

Figure 23: Average values of fine dust in different German cities on the 01.01.2018[34]

Second, if you must deal with, for example, contaminated bags do so after you went to the clean areas or change at least your closes and sanitize yourself properly to prevent the spreading of the contamination.

But what about other fungi? That’s a good question and refers to the media as a third contamination vector. It also refers to the mentioned sterilization process. During this process, we reduce the number of bacteria, viruses, and fungus so that our mushroom spores have a higher chance to colonize the now sterile substrate first.

On the same token, we must sterilize our tools. For your scalpel, you can, for example, using an Infrared (IR) sterilizer. This tool heats your scalpel up to 815°C or 1,500°F. After 5-7 seconds, the blade is sterile.

This is one step of many to avoid contamination spreading. The main activity of you will be cleaning the tables, shelves and so on with alcohol and or hydrogen peroxide (max. 5% conc.).

If you are having trouble with contamination you should check out my articles on 18 Ways to Keep Pests in Check and How Do I Prevent Contamination?

With that said I, will stop here to give you time to pause and think about what you just read.

⏩ Mini Course | Get Started with Mushroom Farming

✅ Learn how to start a mushroom farm

✅ Learn what it takes to become successful

✅ Learn about common mistakes

✅ Learn to pick the best mushroom

---