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This is the final part of a three part series. In this part I'll talk about how to get started in mushroom cultivation and give an overview over the most common techniques.
Part one: An introduction to mushroom cultivation
Part two: Sterility in mushroom cultivation
To achieve quick and healthy growth, fungi are provided with different media during their life in mushroom cultivation. The cultivation process can be described in two phases: the creation of spawn and fruiting.
Spawn is a nutritious medium that is colonized by mycelium. To create it, some clean mycelium is usually first grown and selected on agar-agar plates and then expanded on some type of grain, e.g. rye. The processes for this are mostly the same for any fungus.
To prepare for the fruiting phase, the created spawn is mixed with some substrate that provides moisture and potentially more nutrients to the fungus. This substrate depends on the species of fungus. An oyster mushroom, for example, will often be mixed with moist sawdust, as this fungus also grows on wood in the wild. Once the mycelium has taken hold of the newly introduced substrate as well, it is ready to form fruit bodies, that we can harvest once mature.
To encourage the formation of fruit bodies, the fungus is introduced to fresh air in an environment with high humidity. At this point contamination is less likely, because the fungus has already colonized all nutrients.
Before we can begin, we need to acquire a fungus. The two most common forms that you can buy are spores and "mycelium syringes". For a beginner, I would strongly recommend starting with a mycelium syringe, since you can skip the time consuming work of germinating spores and developing some clean mycelium. Nonetheless I'll briefly shine a light on all the different forms of a fungus you could start with.
Spores usually either come as spore prints or spore syringes. The syringes contain sterile water in which the spores are dissolved and are a little easier to use. Spore prints are usually aluminium foil onto which the cap of a mature mushroom had been placed to drop its spores. Spores can be stored for years and are well suited for trading with other cultivators. They are often not completely contamination free, so it is recommended to grow and select some clean mycelium on agar-agar from your spores first.
Mycelium is mostly sold as mycelium syringes, where the mycelium is dissolved in sterile water together with some nutrients. This is also called a "liquid culture". The mycelium is contamination free and will quickly start expanding when introduced to new nutrients.
You can also buy already colonized spawn or ready-to-fruit grow kits for some common species, if you want get a quick start.
Once you collected some experience, you can also start your own culture by cloning a fresh specimen from the supermarket or from the forest. Taking spores from collected, wild specimen is also possible.
Before we dive into the specific techniques, here is an overview of common components in mushroom cultivation and typical transitions between them. This is by far not complete, but enough for the first few months in this hobby.
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Agar-agar is a substance that can be combined with water and some nutrients to create a solid, translucent medium, that mycelium grows well on. In microbioligy, this medium is often used in petri dishes. It is great for creating and selecting healthy mycelium, because it provides a 2D surface where all contaminants can easily be spotted.
To create the medium, a solution of water, nutrients and agar-agar must be heated and when it cools down again, it will solidify. In a professional laboratory, the heated liquid is sterilized, poured into sterile petri dishes and sealed for later use.
Recreating this process as a hobbyist is complicated and petri dishes can be hard to obtain, but fortunately things can be simplified. So called "no-pour techniques" are used by many hobbyists, where jars or transparent plastic containers are filled with the medium in an unsterile environment and then the whole container together with the medium are sterilized in a pressure cooker afterwards.
Once we've got some agar-agar plates we can start germinating spores to create mycelium. We will need to set up the still air box (SAB) with our agar-agar plates and spore print or spore syringe inside. Then the agar-agar container is opened and spores are placed at the center of our dish with a sterile tool, before closing the container again.
If everything works, we will see some mycelium developing after a few weeks. If contamination became visible in the meantime, the dish is unfortunately not usable anymore and it's contents should be disposed.
The mycelium that starts growing will probably look unordered and messy at this point. This is because a lot of spores have germinated and mycelium with different genetics is growing in the same place. This is called "multispore culture". By selecting the healthiest mycelium and propagating it, a quick growing strain can be obtained.
The selection is done by simply (in sterility, inside the SAB) cutting out a little square of the outer edge of the desired mycelium and placing it in the middle of a new agar-agar dish. The mycelium will continue to grow in the new dish. It is probably still not a single strain of mycelium after the first transfer, but if you repeat this process for a few times, you will end up with some uniformly growing, fast mycelium. This is the ideal starting point for creating healthy spawn.
Once you have isolated some mycelium you like, it can be stored long term on an "agar-agar slant" in the fridge, but describing this in detail goes beyond the scope of this article.
Clean mycelium can also be grown inside a nutritious liquid, called a "liquid culture". Working with liquid cultures speeds things up, as it is easier for the mycelium to grow through liquid than across solid agar-agar. However, the chances for contamination are higher with liquid cultures, so I wouldn't recommend them for beginners.
Spawn is an intermediate step before moving the fungus to it's final substrate. It is used to grow the mycelium and provide it with a lot of nutrients, that will later be used to create fruit bodies. Most commonly some form of grain, like rye, is used to create spawn.
To create spawn, the grain of choice will be soaked with water and boiled until soft. In this form, the grain is most easily consumed by the fungus. The grain is then filled into jars that have been equipped with an air filter in the lid and sterilized in the pressure cooker.
To inoculate the spawn, some mycelium from agar-agar or a liquid culture is placed in the jar in a sterile setting. Colonization of the whole jar then only takes a few weeks. One colonized jar of spawn can also be used to inoculate other jars, allowing for rapid multiplication.
Once we have created enough spawn, we can move the fungus to its final substrate. It will depend on the species you are growing, but all the recommended ones for beginners like to digest hardwood.
Hardwood is cheaply available in the form of fuel pellets, which are just compressed saw dust. The container for the final substrate is often a special "growing bag", but people have also grown mushrooms in buckets and other containers.
Because these final containers are often large, it is impractical to work with them in the still air box. Fortunately, we can get away with being unsterile at this point, since the spawn gives our fungus a head start over contaminants and the final substrate is not that nutritious anyway, so it's not as attractive to those antagonists. However, we can still "pasteurize" the saw dust, which will kill most intruders. This is simply done by mixing the fuel pellets with boiling water and letting it cool down before use.
After mixing the prepared substrate with our spawn, the grow container is closed and we wait until the whole medium is colonized. Then it is time to signal to the fungus, that it can start producing fruit bodies.
This is done by opening the container to fresh air. At this point we need to provide an environment with high humidity, which can be achieved by placing the fungus in a tent or large tote that is sprayed with water every day or so. More automated setups like a "martha tent" are also possible.
If everything goes right, fruit bodies will form within a few weeks. After the first harvest, the fungus might produce new fruit bodies again. Sometimes even a third "flush" will grow.
I hope to have given you an understanding of what goes into mushroom cultivation at home. Of course, I have not even closely covered all the different techniques that are out there and the ones I described I have merely sketched roughly. If I was able to spark some interest in you, I encourage you to read more about the mentioned techniques. A few good resources are those:
shroomery.org, an age old forum that has a very active community and loads of tutorials (TEKs)
The /r/MushroomGrowers subreddit
SouthwestMushrooms, the YouTube channel of a commercial cultivator