Shiitake mushrooms

We’ve been experimenting with log-grown shiitake mushrooms as an interesting diversification for our farm, which has abundant woodlands in need of thinning. Raising mushrooms this way has many benefits for us: it uses primarily on-farm resources (logs, labor, and time) at relatively low cost; it increases our product offerings while utilizing a portion of the landscape that is otherwise not suitable for food production; and the primary work happens during February, an otherwise (relative) down-time on the farm. This is an excellent example of the economic and environmental value of diversification on a small farm, and we’ve enjoyed getting started in the practice.

Under our system, we cut and inoculate approximately 40 new logs every year. Given that logs ought to last 3-5 years, we hope that long-term this will give us a steady rolling supply of up to 200 logs producing in any given year. We can inoculate 40 fresh-cut logs, start to finish, in a day with just two of us.

We’ve put a fair bit of thought and experimentation into developing our methods for inoculating and handling the shiitake logs, which we’ll share in a photo essay below for others interested in trying this. Our practices are heavily informed by the books Shiitake Growers Handbook and Growing Shiitake Mushrooms in a Continental Climate (in revision as of 2012); University of Missouri Agroforestry Publication AF10-10, Growing Shiitake Mushrooms in an Agroforestry Practice, has also been very helpful. Our mushroom-specific supplies have come from Wisconsin-based Field & Forest, who has also given us good support when needed. Please understand that the methods and ideas below are presented on a “how we do it” basis rather than a “how you should” basis; this is primarily for illustration and inspiration, and you should consult other reputable sources before embarking on anything. In particular, please note that handling hot mushroom wax can be quite dangerous and you should research the relevant details beyond this page.

Our first step involves selected appropriate trees and cutting logs in the first place (above). We use primarily oak (red & white) and maple, but are experimenting with other tree types as well. In early-mid February we walk our woods, looking for straight trees with trunks 3″-8″ in diameter, which are overcrowded or should otherwise be thinned to improve the woodlot overall. We mark these with yellow flagging for later. We do the actual logging in February, when we’re almost ready to inoculate, cutting the trunks into 4′ sections and bringing them back to our barn, sometimes storing them under a clean tarp to conserve moisture. We cut more than we need, as some are rejected during the inoculation process; one side benefit to mushroom work is that the best tree species are also good firewood. To us, logs shorter than 4′ aren’t as efficient to handle, longer than 4′ are too unwieldy, and any 4′ rejects divide perfectly into three 18″ firewood chunks that fit our wood stove.

Above, our actual inoculation setup involves a series of beams on sawhorses that allow the logs to be gently rolled along between work stations, allowing easy access to the logs at all work stations while limiting the need for lifting and handling. Clockwise from upper left: fresh log pile, drilling station (upper right), inoculation station (lower right, spawn in bucket), waxing station (lower left, hot wax pot behind sawhorse), workbench in middle with all accessories.

Above, a close-up look at fresh logs of various diameters, and a 5 lb package of shiitake spawn (sawdust colonized by shiitake mycelium). This package will inoculate around 20 logs.

Above, the drilling process. Each log needs a series of holes drilled to a specific depth, into which the mushroom spawn will be inserted and sealed. We use a high-speed drill with a specialized mushroom bit whose collar stops the hole at the right depth; this is well worth the investment. Holes are drilled in a diamond pattern like that at upper right, along the length of the log and around the circumference.

Above left, a special inoculation tool with a metal plunger is jammed into the spawn bin, packing a properly-sized plug of sawdust-spawn into the tool. Above center, the tool is placed over each pre-drilled hole, and the plunger struck to jam the spawn plug down tightly into the hole. Filling the hole properly is critical; holes should be packed tightly with spawn but not mounded. Above right, a broader view of Eric working his way along a log.

Above, sealing in the spawn with hot wax; this helps to maintain moisture at the inoculation sites. Center, keeping the wax melted over a camp stove, using a candy thermometer to regularly and carefully monitor temperature. We haven’t found an affordable hot plate that is up to the task of keeping wax hot for hours. The camp stove method is somewhat more dangerous because of the open flame, so we exercise extreme caution when working near the wax. We do not heat wax above 400ºF because overheated wax will start a fire. (We always keep a fire extinguisher nearby just in case.) On the other hand, wax that isn’t hot enough won’t seal the hole properly. Left, using a dauber to apply wax to a spawn hole. Right, Joanna working her way down an inoculated log. Note the little strip of cedar parallel to the log; that’s a stopper to keep the log from rolling out of position while each row is sealed.

Above, another overall view of the work zone, showing how different logs are positioned along the rollers to move easily between stations. Logs start at the upper right (drilling), are rolled to the lower right (inoculation). After inoculation, the log is lifted and rotated 90º to the next set of rails for waxing (lower left of photo). We like the setup with the 90º bend rather than a system in which the log rolls along a straight set of rails. Our system means that the person doing inoculation can stand in front of the log rather than reaching in from both ends. We think it’s more ergonomic and efficient overall to gently lift each log a quarter-turn onto the next rollers than to lean far over each one from the side, or have two people working from opposite sides. This is why three workers are ideal; when we do this with just the two of us, we rotate around jobs as needed. When someone has down time, there are also minor tasks such as labeling the logs with aluminum tags (to note tree type, inoculation date, & spawn strain).

Above, freshly inoculated logs, stacked low to the ground to take advantage of soil moisture, but set up on cedar planks and logs to minimize direct soil contact (and thus contamination with soil fungi). We’re still experimenting with optimum stacking patterns for our climate. These are set up beneath a thick canopy of cedar trees, which shades the logs and helps capture moisture. The location is next to our vegetable packing barn, to help us remember to monitor the logs. Certain logs also have metal hooks in the end so we can hang them from a scale; monitoring log weight is a good proxy for moisture content and thus spawn health.

We had set up a nifty system for capturing used produce wash water and pumping it onto the mushroom logs, but found that in mid-late summer when the irrigation needs were highest, we also weren’t generating much wash water as most summer produce like tomatoes, peppers, beans, and so on actually don’t need washing. We’re still experimenting with soaker hoses and sprinklers to find the best way to keep logs moist in a dry year, like 2011 when we got little to no meaningful rain through summer and fall.

The hoped-for final product, delicious fresh shiitakes. These can grow, and overgrow, really fast, so it’s important to have the logs set up in a place where you’ll walk by regularly or otherwise remember to check on them. Overgrown mushrooms make a tasty broth, but aren’t particularly marketable.