A Simplified Overview of Mushroom Cultivation Strategies
by Paul Stamets
Mushrooms reproduce through spores. In the highly competitive natural world, the chances of mushroom spores germinating and then producing a mushroom are slim. Within a laboratory, isolated from airborne contamination, the probability of success is much improved. What a cultivator does is remove a select species from the fierce competition of outdoors into an optimized environment indoors wherein the mushroom mycelium grows unhindered from the ravages of nature. This harbor of quiet refuge is, in effect, the sterile laboratory. Contrary to popular belief, such an inoculation room can be easily constructed at modest expense within your home.
A mushroom culture can be taken from spores or from tissue. In germinating spores, many strains are formed, some compatible with one another, some not. In taking a tissue culture (clone) from a living mushroom, the cultivator preserves the exact genetic character of the contributing mushroom. With spores, a single strain must be selected from the multitude of strains created. In both cases, the result is a network of cells called, collectively, the mushroom mycelium.
Once a pure strain has been developed, the next step is to increase the mycelial mass. (See our Pictorial Overview of Mushroom Tissue Culture and Cultivation.) This is done by first growing the mycelium on enriched agar media in a petri dish and then on grain or sawdust/bran. On the flat, two dimensional plane of a petri dish, contaminants such as molds and bacteria become readily apparent. Since it is easy to see if mushroom mycelium is pure and free of contamination, experienced cultivators propagate mycelium in petri dishes and then inoculate grain or sawdust/bran that has been sterilized in jars. When these grain or sawdust filled jars (denoted as G1 Masters) have grown through with mushroom mycelium, they are called SPAWN, and either can be individually used to inoculate another 10 to 20 more grain-filled jars, designated as (G2), or to inoculate bulk substrates such as straw, wood, or compost. G1 masters are best grown out in regular mouth quart mason jars; G2 spawn is best grown out in regular mouth half gallon and/or gallon jars. Another generation of spawn, designated as G3 can be created from G2, if desired. No more expansions from grain-to-grain transfers should be made beyond G3 as contamination often can occur and not be detected until it is too late.
In contrast, liquid culture allows a cultivator to use as little as one mycelial culture from a single petri dish to inoculate hundreds of grain jars in a fraction of the time it takes with the above-described method. Of course, preferences vary with every cultivator. Mushroom tissue culture is a highly individualized art. However, FP promotes liquid culture as a revolutionary improvement over the more labor intensive, traditional methods.
With many species, grain spawn can be laid out into trays, cased with a moisture-laden soil-like layer, and fruited. Once tissue culture is mastered, this is the simplest way to grow mushrooms. It is also a proven way to "screen" strains for their cultivation potential.
Since the biomass of mushroom mycelium will be exponentially multiplied from a small fragment of mycelium, the sterility of the laboratory is of paramount importance. Micron filters (used in laminar flow hoods) solve the problem of contamination in the laboratory and they more than pay for themselves considering the contamination they prevent and the cultures/time they save.
To the beginner, sterile culture may seem too difficult an adventure to embark upon. The possible pitfalls of sterile culture can be avoided by buying ready-to-inoculate spawn until a familiarity with the process is attained. Ultimately, however, every cultivator should create their own spawn so they are not forever dependent upon others.
Once pure spawn is obtained, the next step varies with the species being grown. Shiitake (Lentinula edodes) calls for the inoculation of hardwood logs or sawdust/bran blocks. Oyster mushrooms (Pleurotus spp.) fruit admirably on pasteurized straw. The King Stropharia or Garden Giant (Stropharia rugoso-annulata) enjoys a habitat composed of wood chips and/or wheat straw. Morels (Morchella spp.) are most easily grown outside in shady sawdust/ash beds. The Chinese Ling Chi, also known as the Japanese Reishi (Ganoderma lucidum) can be grown outdoors on logs buried in sawdust. Chicken-of-the-Woods (Polyporus sulphureus) can be grown on stumps, as can many other gourmet species. Lastly, the classic white button mushroom (Agaricus brunnescens) fruits on horse manure/straw compost. Most mushrooms capable of being cultivated will fruit on one of these aforementioned substrates.
After the mycelium has fully colonized the substrate, mushroom formation should be encouraged. In general, the key to fruiting mushrooms relies on altering the surrounding environment. To change a set of environmental variables in favor of mushroom formation is called an Initiation Strategy. Mushrooms form best when:
Considerable variation exists between species in their fruiting requirements and this subject cannot be adequately discussed here. Hence, we recommend the most comprehensive books on the subject Growing Gourmet & Medicinal Mushrooms by Paul Stamets and The Mushroom Cultivator by Paul Stamets and Jeff Chilton. More books by Paul Stamets are being written detailing these concepts. By remaining in contact with Fungi Perfecti, you will be assured of having the latest State-of-the-Art information and technology.
Good luck. May your fruitings be bountiful and your lives enriched by the experience of cultivation. Mushrooming is the best combination of a passionate art and a rapidly emerging science. Each one of you can make a contribution. We hope you do.
Copyright 1998 Paul Stamets, all rights reserved.