The Northeast Forest Farming Conference in Danby, VT, which took place earlier this year, introduced attendees to a wide variety of topics, including shiitake mushroom inoculation. Corinna Steinrueck, the forest manager at Warren Wilson College and the Forest Stewards Guild, hosted a session to teach attendees how to grow shiitake mushrooms through inoculation.
The mushroom inoculation process can be broken down into five main steps: cutting, inoculating, natural fruiting, submerging and harvesting. Throughout the entire process, there are two key factors to keep in mind: do not let the log dry out and prevent other fungi from entering and competing with your mushrooms.
The timing of the entire process is important, as it can influence when your mushrooms are ready for harvest and how many successfully grow.
It’s important to realize that a mushroom is a “fruit” – or, more specifically, “the fruiting body of a mycelial network,” Steinrueck explained.
When growing mushrooms on a log, harvesting the mushroom doesn’t harm the log, just as harvesting an apple doesn’t harm the apple tree.
Steinrueck prefers to grow shiitake mushrooms, as they are “the only commercially viable mushroom that will grow on logs” – and they are very reliable. Unlike other mushroom varieties, shiitake can be forced to fruit through soaking, allowing producers to get a consistent crop whenever they decide.
Logs are the growing medium for these mushrooms, so the quality of the log influences the quality of the fruit. A good commercial log should last over four years, but its lifespan depends on a number of factors. The best tree species for log inoculation depends on the mushroom variety. For shiitake mushrooms, the best trees to use include sugar maple, white oak and beech.
No matter the mushroom variety, “you want to harvest young, healthy logs,” Steinrueck explained, ensure proper airflow and determine your ideal log size. A log that is too skinny will decompose very quickly, but a log that is too wide can be difficult to pick up when fully submerged in water. Steinrueck recommended using logs that are three to eight inches wide.
Corinna Steinrueck, the forest manager at Warren Wilson College, led a session on successful shiitake inoculation. Photo by Kelsi Devolve
Steinrueck believes that “spring is the best time to cut your logs” (or any time during the dormant season).
After cutting, the logs must rest for two to four weeks, as they have a natural antifungal property that needs to pass out of their system prior to inoculating. If the antifungal property still remains in the log during inoculation, no mushrooms will be able to grow.
After the logs sit for those two to four weeks, they can be inoculated. The best timing depends on location, but the worst time to inoculate is around budbreak.
Inoculation begins by drilling holes into the logs. The holes are then filled with the chosen shiitake spawn strain and covered with hot wax to keep moisture in (and other fungi out). Steinrueck takes it a step further and waxes both ends of the log as well.
Once inoculation is complete, the log enters its “spawn run,” when the mycelia in the spawn work to colonize the entire log. The length of the spawn run depends on the spawn variety used, the size of the log and the time of year you inoculated.
Overall, a spawn run usually lasts between six and 18 months. During this time, the logs should be stored in the shade, kept off the ground and watered as needed.
When the entire log is colonized and the weather is right, the log will have its first natural fruiting. You will not be able to successfully force-fruit the log until it has this natural fruit on its own. Steinrueck forces logs by submerging them underwater for 24 hours. Within the next three days, the fruit will begin to button, and they will be ready to harvest about one week later.
The steps to inoculate shiitake mushrooms aren’t difficult to perform. The challenging part is getting the timing correct. Once the logs have gone through their natural fruiting, they can be soaked around four times a year, provided you allow a six- to eight-week break between soakings. Although a good commercial log should last at least four years, it will still continue to produce fruit years after, just in smaller quantities.
by Kelsi Devolve
