BASICS OF MUSHROOM CULTIVATION
When cultivating mushrooms, the goal of the mushroom grower is to take the basic knowledge of the mushroom’s life cycle, as described previously, and use it to their advantage to tip the balances in favour of producing healthy, reliable crops of the desired mushroom species.
The key goals of the mushroom grower include:
Provide the right kind of substrate for the fungi to thrive on
Eliminate competing species of fungi from the substrate through sterilisation, pasteurisation, or, in the case of wooden logs, freshly harvested logs that have not yet been colonised by competing organisms
Inoculate the substrate with adequate amounts of mycelium to colonise the substrate before competing organisms get a chance to gain a foothold.
Provide environmental conditions, particularly temperature and humidity, within a range that facilitates healthy and vigorous growth of the fungal organism
A key aspect of mushroom growing is finding the right substrate. The first requirement is, obviously, one that the species you’re growing will actually grow on. Secondly, the substrate needs to be easily and cheaply available. This second point can often lead mushroom growers to always be on the lookout for waste products and other materials that may otherwise be discarded by society, that you could use to grow delicious fungi!
Substrates commonly used for cultivating mushrooms include straw, sawdust, woodchips, freshly cut hardwood logs, and compost / manure. Wood loving mushrooms such as oyster and shiitake mushrooms can be cultivated on a wide range of other carbon rich substrates, including waste products such as shredded paper or cardboard, chocolate / coffee hulls, corn stalks from maize farms and so on.
PREPARING SUBSTRATE FOR USE
Once the right substrate is found, it must be hydrated and sanitised, ready to be inoculated with the desired mushroom culture. This booklet will examine three of the main ways of growing mushrooms: in straw filled bags, on hardwood logs and making outdoor patches on woodchips or straw mulch. The detailed methods of each of these is described in subsequent chapters.
In the case of straw bags or sawdust blocks, which are commonly used as quick turnaround, indoor cultivation methods, the substrate must be pasteurised or sterilised using heat or alkalinity changes to knock back competing microbes.
In the case of wooden logs, the key is to use healthy wood that has only recently been felled. It’s best to try to inoculate your logs within a month or so of being cut - so that your mushroom culture has the upper hand before other spores begin to germinate and spread through the wood. The same applies for outdoor woodchip beds.
INOCULATING SUBSTRATE WITH MYCELIUM
The next step in the process of growing mushrooms is to inoculate the substrate with the mycelium of your desired species. This is achieved by spreading mycelium coated materials (or liquids) through the prepared bulk substrate. This spreadable mushroom culture is called mushroom spawn.
The goal of inoculating is basically to introduce the mycelium culture to as many points in the substrate as practically feasible, and spread out as evenly as possible, so that the mycelium can quickly colonise the substrate before any competing organisms get a chance to take hold.
Compared to bulk substrate (straw, wood etc), making spawn is energy intensive, time consuming and costly. It is often done in laboratory-like conditions. This is why many hobbyist growers choose to purchase pre-made spawn, as it saves a lot of time and effort and potential failures. So it’s about using your spawn material in the smartest and most effective way possible.
For straw bags or sawdust blocks, the spawn material is usually sterilised whole grains (such as barley, wheat, millet etc) that have been colonised by mycelium. This is often done in glass preserving jars with a microbe-proof air filter in the lid to allow for the mycelium to breathe as it grows.
The great advantage of using grains as spawn, is that once they are colonised by mycelium, they can be shaken up back into individual pieces of grain (which are now growing mycelium from them) which means that a single quart jar of grain contains literally thousands of possible inoculation points, that you can spread throughout your substrate and allow for rapid colonisation.
For wood logs, the spawn material is usually wooden dowels that have been soaked in water, sterilised, and then inoculated with mycelium. This inoculation is often done with grain spawn, but can also be done with liquid mycelium cultures or other means.
Fresh logs are cut to the desired length and size and then holes are drilled in them which are the same diameter as the dowel spawn. The dowels are then tapped into the holes where they will begin to spread their mycelium throughout the rest of the wood.
INCUBATION OF BULK SUBSTRATE
Once the bulk substrate has been inoculated, it's ready to be incubated. Incubation is the process of providing enough warmth and humidity to the mycelium while it colonises its domain. In general, a high humidity is best, and temperatures of between 15 to 30℃ are suitable, with mid-20s being optimal.
Once the substrate is fully colonised, which is visually observable by seeing that white mycelium has spread throughout, then it is ready to be put into fruiting conditions.
If given a good environment, most mushroom species will begin fruiting on their own when they are ready to. Obviously, a high humidity environment is important, so that the mushrooms do not dry off or get stunted while they grow.
Asides from providing humidity and letting nature take its course, there are several environmental conditions that can trigger mushrooms to fruit. These include:
A slight drop in temperature compared to incubation temperature (called a ‘cold shock’)
Increased light compared to incubation (i.e. More light than none at all)
A drop in CO2 levels / a raise in oxygen levels (increased air flow)
In the case of wood logs, some species (especially shiitake) can be stimulated into fruiting by vibration. So often, colonised shiitake logs are dropped on the ground or hit with mallets to help trigger a flush of mushrooms. All mushroom logs benefit from being soaked in water overnight to trigger fruiting.