Mushroom cultivation requires an environment that can be maintained cleanly and with appropriate humidity. This will prevent contamination of the substrate by microorganisms that compete with mycelium for water, nutrients, and energy.
Mushroom growers usually select a basement or spare room in the house that can be kept clean and humid. This is especially important during warmer seasons when the air can easily reach dew-point (just like your car windscreen).
Substrate
Having the right equipment and materials to do your mycological work is important, but the biggest source of contamination in mushroom cultivation comes from the substrate itself. Regardless of how clean you are or how sterile your grow room is, the spores and mycelium that will eventually become fruiting mushrooms need to be inoculated with a sterile substrate to get off to a good start.
If you are working with a perlite-based substrate, then you can sterilize the perlite between uses by steaming it in a barrel sterilizer (such as these). Barrel sterilizers hold the substrate at 212degF for long periods of time which kills all microorganisms in the substrate. This leaves a completely clean slate free from competition and prevents new contaminating organisms from getting established.
Another option is to use a cold pasteurization process on the substrate before using it. This technique uses a combination of heating and cooling to achieve the same outcome of killing harmful microorganisms in the substrate, but it also preserves many beneficial ones. This creates an environment where the mycelium will have less competition and will also benefit from the presence of other microorganisms to help with nutrient breakdown and absorption.
You can also sterilize the substrate by mixing it with a powder called Hydrated Lime. This is a fairly organic compound that is made by superheating naturally occurring lime and then adding it to the substrate. This pushes the pH of the substrate up to levels that are hostile to the spores and mycelium, but does not damage or kill them.
It is also important to practice good hygiene throughout the entire cultivation process. This includes regularly wiping down your tools and sanitizing the space where you will be working. Some cultivators even wear face masks to reduce the chance of breathing contaminants into their plates, jars, or blocks.
It is also a good idea to use a laminar flow hood or glove box when handling the spores and mycelium in order to ensure you are working under optimal conditions. Finally, if you can afford it, investing in an autoclave that can handle large loads of substrate for quick and efficient processing is a great way to cut down on the time you spend working in your contaminant-free mushroom growing environment.
Inoculants
A microbial inoculant is a medium that delivers the intended microorganism to the crop. The inoculant must be able to support the microorganisms for an appropriate amount of time to give the plant the bacterial population required for a rhizobia response, resist degradation by indigenous soil microflora and withstand the physical constraints of the soil environment, such as erosion and compaction. The inoculant must also be easy to manufacture, handle and deliver to the farmer, and it must be economical compared to other farm chemicals and used to improve your sterilization technique.
Inoculants must be able to survive through the manufacturing, storage, and transporting process and still be in adequate numbers at the time of seed application (Bashan 1998). The ability to extend shelf life is an important characteristic for inoculants because the fermentation and preparation of inoculum requires time and facilities that are not readily available to growers. Many of the commonly used inoculation media for PGPB, PGPR and rhizobia are designed to work well in laboratory culture conditions under skilled personnel and precise laboratory conditions, but are impractical to use by growers. Many of these media require a high level of refrigeration and have costly additives that reduce cost-effectiveness.
For microbial inoculants, the formulation of the carrier is a key factor for performance. It must be easily manufactured and mixed by the fermentation industry and have an adequate supply of inexpensive raw material. It must be able to accept addition of nutrients, have an adjustable pH and be easily dried for delivery to the farm. Several different formulations have been tested and found to be superior for maintaining the survival of inoculum and rhizobia, including perlite and vermiculite blends, and a sugar beet pelleting material and EBTM-vermiculite mix.
Granular inoculants are the most common in North America possibly because they are easier to handle and less dusty than powder inoculants and are compatible with machinery commonly used on large farms for seeding purposes. Inoculants that are applied in the field have a higher rate of soil inoculation and provide greater protection to the inoculum than inoculants stored and transported under refrigeration.
Containers
The most important element for mushroom growers to consider is the containers they use. The container will serve as a home for the substrate and mushroom mycelium, so it is critical that the containers be sterile. This is especially important at the spawning stage. The spores and mycelium are vulnerable during this time, and if they come in contact with competing fungus, mildew or mold, the entire substrate may be destroyed and you will have to start over again. Keeping your tools, hands and work space clean using disinfectant and isopropyl alcohol will help you keep contamination levels low and avoid the heartache of losing a crop to competing organisms.
Spawning is when a liquid culture or spores are introduced to the substrate and colonize it, turning it into a mushroom crop. Once spawn has colonized the substrate, it must be grown into fruiting blocks or bags to produce mushrooms. This process requires the mycologist to have a very sterile environment, and this can only be accomplished in a sterile room or by using a flow hood (fan powered HEPA filtered device that produces a laminar flow of uncontaminated air across your workspace).
During spawning, the spores are isolated on a sterile medium such as grain to create grain spawn and then mixed into supplemented and sterilized substrate to form the block or bag that will fruit mushrooms. This is done under a microscope with skilled techniques in a sterile room, and it is impossible for a home grower to reproduce this type of facility for their own mushroom spawning.
Once the spawn has been sterilized, it is ready to be mixed into the substrate and soaked with water to hydrate the material. This is also a great opportunity to add any other supplements that will improve your spawning results such as glycerin, kelp meal, cottonseed hulls or agricultural byproducts such as straw and coffee grounds.
Using tubs for containers makes it easy to move the jars around if you have family and friends drop in unexpectedly, as they don’t usually notice a mushroom jar hidden away in a closet! Tubs are also simple to clean and sterilize between harvests, and there aren’t any grooves or nooks where contaminants might lurk.
Grow Room
A fungus, virus or bacteria can take hold in your grow room like the bad guys in a B-movie. Moisture, heat, soil and nutrients are the ingredients for a perfect feast for these ruthless invaders. But the good news is that cleanliness is the hero in this story, stopping these villains before they can cause harm to your plants. The key is regular cleaning and sterilization, especially between grows.
Many cultivators use a sanitizer before and after each growing cycle to eliminate organic threats. Often, a simple wiping will do the trick, but between crops it is more effective to soak hydroponic systems, containers and cloning structures in a chemical cleaner. This will kill the most resistant spores, and vaporized disinfectants are ideal for sanitizing surfaces with all their nooks and crannies.
It is also important to sanitize tools such as scissors, pruners and other gardening implements. A simple cut from a pair of dirty clippers can spread disease across the plants in your garden. It is recommended to sanitize the cutting instruments with a diluted solution of bleach or hydrogen peroxide before using them on new plants.
In addition to sanitizing surfaces, it is also important to regularly clean up water that accumulates on floors and equipment. This will prevent puddles from becoming a food source for fungi such as mold and mildew. Many cultivators will set up spore traps in their grow rooms to monitor for unwanted pathogens and then treat them with a fungicide before they can affect the plants.
Keeping up with regular cleaning and sanitizing will prevent many problems, but sometimes fungus, viruses and bacteria will still find their way into your grow. In this case, it is helpful to have some fungicides and insecticides in your tool box so you can treat the problem right away.
Thoroughly sanitizing your grow room between each harvest will help to minimize the need for costly crop sprays and treatments that can damage plant health and yield. Proper sanitation will also ensure that your plants can use all of their energy to grow rather than fighting off diseases and insects.
