Biologically, forest cultivation of mushrooms involves fungal decay of an organic substrate, usually wood. The substrate is the “food source” for the fungus that allows the fungus to grow and eventually produce mushrooms. It is a rotten business to be sure. The process consists of four stages:
- Substrate Acquisition. For the most common forest-cultivated mushroom, shiitake, the substrate consists of wooden logs cut from live trees. The recommended size for logs is 3 to 4 feet long and 4 to 7 inches in diameter (manageable to lift and move, especially if moist). Most hardwood tree species will suffice, but some, such as oak because of its density, are better than others. Conifers are not suitable. Logs are usually cut in the late winter or spring before buds swell.
- Substrate Inoculation. The fungus must be brought into intimate contact with the substrate (log). Fungal spawn is used for inoculation. Spawn consists of the vegetative mycelium (threads of the fungus, not spores), mixed with sawdust or other substrate material to colonize such as wooden plugs. In most cases, sawdust or plug spawn is purchased from specialty-spawn producers. About 30 holes are drilled into the log (15 cm/6 in. apart, in offset rows), and spawn is inserted into the holes, and then molten wax is applied to seal the holes. Many producers use food-grade wax, while others use canning wax. It is important to note that the sooner the inoculation activity can be done following felling the live tree the better. This way, the mycelia have a fresh start from competing with natural fungi and bacteria already present in the surrounding environment.
- Substrate Colonization. For this stage, inoculated logs are placed under a tree canopy or artificial shade to prevent them from drying out. Monitor rainfall and consider irrigating to prevent the logs from drying. Various strains of a species may be available, so check for one that best matches your temperature and production conditions. During colonization, the fungus begins to decompose (eat, rot, decay) the wood substrate and moves farther into the wood as colonization proceeds. It takes about six months to a year (more or less, depending on your climate) for the fungus to completely colonize the sapwood. At the end of this period and when moisture and the temperature are sufficiently high, the log is ready to produce mushrooms.
- Mushroom Production. Known as fruiting, mushroom production will begin naturally when the log is fully colonized and the temperature is between 65° to 80°F. Again, you may want to consider irrigating the logs to control substrate moisture levels. Natural fruiting is sporadic and unpredictable, which is fine for home use, but mushrooms are usually “forced” to meet the scheduling demands of the market. Forcing (shocking) is accomplished by completely immersing the log in water for 12 to 24 hours, after which the logs are stacked or leaned against a rail or a tree, for about a week. After several days (seven to 10 usually), the small mushroom primordials (pins) begin to form; and several days later (temperature/moisture dependent), the mushrooms are ready to harvest.
Although the details differ for forest cultivation of other specialty mushrooms such as oyster, lion’s mane, and stropharia, the same four stages must occur in order to successfully produce these tasty, nutritious, and potentially income-generating non-timber forest products.
© All photos in this article are courtesy of Dr. Kenneth Mudge of Cornell University.
For additional information on mushroom production, visit the pages below.
For more information specific to growing Shiitake Mushrooms visit the following guides from the University of Kentucky Cooperative Extension Service: