There are many factors that need to be considered when selecting logs and creating a laying yard for growing shiitake mushrooms. This fact sheet provides helpful instructions and insights into the best locations, stacking methods, moisture content, and more.
Following log inoculation, the spawn run begins. This is essentially the incubation period until the fungus begins to fruit. This can take anywhere from six months to two years depending on a number of factors:
- choice of strain
- amount of spawn used in the inoculation
- size of the log
- log moisture
The shiitake grower’s objectives are to maintain log moisture content above at least 30% to ensure speedy, vigorous, uniform colonization, and to provide an environment with enough ventilation to inhibit excessive growth of weed fungi. If moisture drops below 25%, mycelial death may occur. Also, logs should be adequately protected from abrupt or severe drying, which causes shrinkage, cracking, or checking (lengthwise cracks) on log surfaces. Even small cracking or checking of the bark can create extra surface area for drying, resulting in new sites for weed fungi to enter the log. Keep in mind that the optimum temperature for spawn growth is 72–77 degrees Fahrenheit (log temperature). Temperatures above 105 F are generally lethal to the shiitake fungus.
The choice of location for a laying yard and the choice of log stacking method can greatly reduce the need for management activities such as irrigation, the use of temporary covers to screen wind and sun, etc. If, for example, the laying yard is on a high, open, windy, sunny hilltop, the drying rate of logs might necessitate regular and frequent irrigation along with artificial windscreens, sunscreens, or coverings on the logs. If this is the case, growers will need access to clean water. A different location with lower winds, less sun, and higher humidity might be more favorable and require less active management. A laying yard located behind the north side of buildings or under coniferous trees works well to decrease maintenance. In general, warm, shady areas with good air circulation and protection from wind gusts are excellent sites for laying yards.
Stacking methods also affect log moisture content and drying rates. There are five main types of stacks:
- dead piling (or firewood style)
- A- (or X-) frame stacking
- crib stacking (or crosshatch)
- Japanese hillside stacking
- lean-to (or diagonal) stacking
Variations of these methods may be required depending on site conditions.
Dead piling (Fig. 1) is used mainly for short-term storage, such as when logs come off the inoculation line or for early incubation (temporary laying). It includes using a moisture resistant covering of cloth, plastic, etc. to conserve moisture and shed rain.
Dead piling is not used indefinitely because of the lack of ventilation and the potential for the stack being contaminated by heavy rains or condensation. Dead piling is most useful when the logs require moisture replenishment because of drying or water consumption by spawn growth.
High A-Frame Stacking (also known as X-Frame Stacking)
This stacking method (Fig. 2) is suited to long-term laying only on humid and calm sites where other stacking methods lead to excess surface moisture and mold growth. Due to its low density (efficient use of space) and high ventilation, it has limited use for most growers during the spawn run. It may be more useful during fruiting periods with higher humidity and lower drying rates.
High A-frame stacking requires some form of support for the logs to remain upright. Growers should use a base—gravel, a tarp, timber, etc.—that prevents the log ends from coming into contact with the ground.
Cribbing (Fig. 3) during the spawn run (long-term laying) is probably best suited to airy locations in consistently humid climates with ample, regular rains. It is implemented frequently in shiitake production in Northeastern United States. Cribbing can provide good space efficiency, and it is simple and convenient. However, it has the potential for problems. Rain shadow effects (areas in the stack that are sheltered from rain) can be pronounced. Ventilation and relative humidity tend to vary from the stack’s top, bottom, inside, and outside. Solar gain and temperature also vary from side to side and top to bottom. The higher the cribs are made, the greater the variances.
Growers using this method should space logs 1 to 2 inches apart to allow for adequate aeration. Use a pallet or fresh cut logs as a base for stacks to keep your inoculated logs off the ground. Placing smaller logs in the center of the stack will balance the stack better (Mudge et al. 2013). Use logs of the same tree species that were felled the same day. Logs felled more than two days apart should not be placed in the same crib stack.
Japanese Hillside Stacking
This stacking technique (Fig. 5) is modified from the crib stack and is designed for especially steep locations. Stability is increased using this method on hillsides. Logs are slightly raised off the ground, resulting in reduced pest pressure and improved aeration. It also allows for easy harvesting of the mushrooms. This method may be most useful to growers in southeastern Ohio (Mudge et al. 2013). Watch this video to learn more about the Japanese hillside method: youtube.com/watch?v=aMsqJNjS6Bg.
Lean-to stacking (Fig. 6) is probably the most broadly applicable method. It is certainly the most flexible method and can provide a high degree of uniformity throughout each stack.
Lean-to stacking enables the grower to maximize or minimize rain shadow effects (areas in the stack that are sheltered from rain) by either using the same number of logs “vertically aligned” in each course or by setting them out of alignment. Rainfall exposure may also vary by changing the angle of logs. The nearer to vertical the logs, the less surface area exposed to rain; the nearer to horizontal, the greater the exposure (Fig. 7). Additionally, steeper angles may also speed runoff of rain from the log surface.
The angle of stacking with this method also affects air flow in the stack. Air flow increases distinctly at even small elevations above the ground surface. Stacking logs at low angles not only places them in a zone of normally lower air speeds, but it is also more apt to deflect air movement aloft, while higher log stacks allow for more air penetration. The angle of stacking also affects the relative humidity of the air to which logs are exposed. Just as air speed changes with small elevations, so does relative humidity of the air. Relative humidity may be quite different at three inches above the ground than at three feet above ground. This difference is more pronounced on some sites than others. Wet or heavy soil and low vegetation that transpires moisture (grass for example) accentuates this effect.
In practice, lower stack angles are appropriate for relatively dry climates or sites and for log sizes or species that are prone to excessive drying. Steeper angles are indicated for humid, rainy climates, calm sites, or with logs less prone to drying. Growers who experiment with lean-to stacks may find that five-degree changes in stack angles can cause significant differences in log moisture content over several weeks or months.
A management opportunity that is unique to lean-to stacking is the ability to regulate solar gain of the logs, which also regulates the daytime temperatures of the logs. Lean-to stacks with the north ends of their leaning logs elevated result in a higher solar gain for each log than stacks with their south ends elevated.
A grower in a cool climate can use this effect to speed colonization by warming the logs. This arrangement can also lengthen the growing season in the spring and fall in many locations. Growers in very warm climates might elevate south ends of logs to minimize solar gain.
Solar gain is greatest where there is full sunlight, but logs should be located under forest shade or approved shade cloth. Growers may also alter the stack orientation to benefit from other site-specific conditions such as openings in a forest canopy, the direction of prevailing winds, or up-slope/down-slope air currents that occur in hilly terrain due to daily heating and cooling.
The variables and effects to consider for shiitake production apply to all stacking methods. The application of these methods will depend on the site and will not yield the same uniformity of drying rates, moisture regain, ventilation, or solar gain. A shiitake grower who has not experimented with a wide variety of stacking methods may be missing beneficial opportunities, not only in providing optimum spawn growth and reducing contamination, but also in making the best use of weather and minimizing labor and material input.
Hill, Deborah B., and Marcella Szymanski. 2010. “Kentucky Shiitake Production Workbook.” FOR-81. Lexington: University of Kentucky Cooperative Extension Service. PDF.
Mudge, Ken, Allen Matthews, Ben Waterman, Bridgett (Jamison) Hilshey, Steve Siergik, Nick Laskovski, Steve and Julia Rockcastle, and Steve Gabriel. 2013. Best Management Practices for Log-Based Shiitake Cultivation in the Northeastern United States. Northeast Sustainable Agriculture Research and Education. Burlington, VT: The University of Vermont.