Timing of Log Cut for Optimum Shiitake Production

by Joe Krawczyk

Last month a feller/buncher showed up on our property to begin the harvest of our oak woodlot. The plans made to cut the trees had been in the back of my mind for a over a decade, but was spurred on now by the introduction of Oak Wilt into the stand of the nearly century old Pin Oak trees. The Oak Wilt fungus travels along the wood vessels, tree top to roots and back, and moves from tree to tree via roots grafted (remember it's cousin, Dutch Elm Disease?), eventually infecting much of the stand. Pockets of trees are often dead within a growing season. So, the time is right to salvage what we can of the wood before infection and also release the suppressed pine, oak (and likely red maple and buckthorn) seedlings, eager for light on the forest floor. Plus, the cut will actually pay off this fall in terms of abundant tops to harvest shiitake logs cut away from the saw logs going to the sawmill. The timing of the harvest could not have been better.

This twist of fate, and happily somewhat good planning, has resulted in the trees being felled at the optimum time for harvest. By now (November) we will be done considering raking leaves and the lawn and garden equipment should stowed for the winter, plus the color change coincides perfectly with what we know of good timing to harvest logs for mushroom cultivation.

Pin Oak logs, many of them old friends, harvested before succumbing 
to Oak Wilt, as shown at the pocket of standing trees, left.

Planning your harvest to coincide with inoculating mushroom logs

Cutting in fall: The optimum time to cut mushroom wood in the fall is when the forest canopy color has changed by one third. This indicates that the trees are dormant and the stored carbohydrates in the sapwood are at their highest levels. An added benefit to this is also that the cells have not completely hardened off and if a fall inoculation is done, shiitake will be able to easily colonize this wood.

If loggers are conscientious, oak tops are in great shape for cutting into shiitake logs.

Cutting in winter until spring bud swell: This is not to say that wood cannot be cut during the rest of  the dormant season. We are not all such good planners ;^ and sometimes nature makes the plan for us (Hurricane Maria for example), while other projects pop-up which take precedence over cutting shiitake logs.  Still, while acceptable mushroom logs can be made from logs felled almost any time of the year, with a few important exceptions with soft hardwoods, the best mushroom logs should be cut while dormant to take advantage of all those sugars stored for winter. In oak, the wood cells will become harder later in the dormant season, say towards spring bud break, making colonization by the mushroom fungus just a little slower. This overall is not a hindrance to colonization of the wood by shiitake, but evidence points to early dormancy (fall cut) to be superior, especially when paired with using heated and humidified indoor incubation methods in cold climates over the winter, or for outdoor incubation in the south.

Log storage and aging; judging how long wood can sit before inoculation 

Let’s assume you can cut logs now but your schedule will prevent you from inoculating until spring of the following year. The good news is that the logs can be overwintered as long as they are protected from direct sunlight and excessive wind. This allows you to take advantage of the benefits of fall cut dormant wood. When it is time to inoculate in the spring and you worry that the logs might be too dry, the logs can be soaked in water for a day or so before they are inoculated. The idea is to maintain 35-45% moisture content while making sure the wood cell "vitality" has declined. Over the years, we have heard rumors of a mysterious antifungal compound that is found in freshly cut logs that will prevent and/or kill shiitake spawn. This mysterious compound, in a round-about way, is water. Shiitake is a saprophytic fungus, i.e., it will not colonize living wood. So for it to begin the decay cycle, the host cells must be dead. This is accomplished by allowing the wood, after cutting, to go through a slight drying phase. Measuring this phase is difficult as this will vary from location to location, by tree species and log diameter. In some regions of Japan where rainfall exceeds 60 inches/year, six to eight weeks drying is a normal. In drier climes, this time would be considerably shorter. There is no hard and fast rule. We often hear “two weeks max” and though this may be true under certain conditions (trees cut during the growing season) and some very arid parts of the country, it certainly isn’t a hard and fast rule for the eastern U.S.  The best way is to watch your wood once cut, taking note especially of the condition of the log ends. Slight cracks radiating out from the center indicate a wood ready for inoculation; deeper cracks (wide enough to allow a dime in) indicate the log should be inoculated asap or soaked in water before inoculation.

Freshly cut limb wood from oak harvest. Note the fabulous sapwood.

If you do cut wood in the fall for storage until a spring inoculation, do keep the wood protected and covered if it is exposed to wind and sun. We store the logs in a large, dense (deadstacked) pile on the north and shaded east side of a building and cover the exposed parts. After you've collected the wood though, don't forget to bring in the rototiller :/

Good thing I wrote this post... so busy in the woods I nearly forgot about yard clean-up!