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Shiitake Mushroom Production:Logs and Laying Yards

by Ohio State University Extension    

Stephen M. Bratkovich, formerly of Ohio State University Extension,
Mitch Gilbert, formerly of the Forest Resource Center, Lanesboro, MN.

Following log inoculation, the shiitake mushroom grower's objectives are to maintain log moisture content above 35 percent, ensuring speedy, vigorous colonization and to provide an environment with enough ventilation to retard excessive growth of weed fungi. Also, logs should be adequately protected from drying that is so abrupt or severe as to cause shrinkage and cracking or checking on log surfaces. Even small cracking or checking of the bark provides extra surface area for drying and new sites for weed fungi to enter the log.

The choice of location for a laying yard and the choice of log stacking methods can greatly diminish 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 a high, open, windy, sunny hilltop, the drying rate of logs might necessitate regular and frequent irrigation and artificial windscreens, sun screeens or coverings on the logs. A different location nearby might be more favorable: lower winds, less sun, higher humidity and less active management.

Stacking methods also affect log moisture content and drying rates. Figure 1 shows four types of stacks: dead piling (or firewood style), "X" (or "A") frame stacking, crib stacking (or cross-hatch) and lean-to (or diagonal) stacking.

Dead Piling

Dead piling is used mainly for short-term storage, as when logs come off the inoculation line, or for early incubation (temporary laying), with 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 potential for contamination if heavy rains penetrate the stack or condensation occurs. Dead piling and covering are probably useful only until the logs require moisture replenishment because of drying or water consumption by spawn growth.

X Frame Stacking

This stacking method 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 low density (space efficiency) 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.

Crib Stacking

Cribbing during spawn run (long-term laying) is probably best suited to airy locations in consistently humid climates with ample, regular rains. However, it has potential for problems. Rain shadow effects can be pronounced. Ventilation and relative humidity tend to vary from top to bottom and from inside to outside of the stack. Solar gain and temperature are also unequal from side to side and top to bottom. The higher the cribs are made, the greater the variances.

On the plus side, cribbing can yield good space efficiency and it is simple and convenient. While some growers may find it to be economical, relatively few will find it to be biologically optimum.

Lean-To Stacking

Lean-to stacking 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 by either using the same number of logs "vertically aligned" in each course or by setting them out of alignment (Figure 2). Rainfall exposure may also be varied 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 (Figure 3). Additionally, steeper angles may also speed runoff of rain from the log surface.

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. In stacking at low angles, not only are logs in a zone of normally lower air speeds, but the low stack is more apt to deflect air movement aloft, while the higher stack will allow more air penetration. Angle of stacking will also affect 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 it is at three feet. This difference is more pronounced on some sites than others. Wet or heavy soils and low vegetation that transpires moisture (grass for example) accentuate 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 with humid, rainy climates and calm sites or with logs less prone to drying. Growers who experiment with lean-to stacks will often find that changes of stack angles of five degrees 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, in turn regulating the daytime temperatures of the logs. Lean-to stacks with the north ends of leaning logs elevated give each log higher solar gain than stacks with south ends elevated.

A grower in a cool climate can use this effect to speed colonization by warming the logs somewhat. 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 (Figure 4). Optimum temperature for spawn growth is 72 F-78 F (log temperature) and temperatures above 105 F are generally lethal.

Solar gain is greatest where there is full sunlight but will still be present under forest shade or most types of shade cloth. Growers may also alter stack orientation to reflect other site specific conditions such as openings in a forest canopy, direction of prevailing winds or up-slope/ down-slope air currents that occur in hilly terrain due to daily heating and cooling.

Summary

The variables and effects in lean-to stacking that have been discussed apply to the other styles of log stacking as well in varying degrees. It should be emphasized though that most other methods will not yield the same uniformity of drying rates, moisture regain, ventilation and solar gain. A shiitake grower who has not experimented with a wide variety of stacking methods may be missing important 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.

Reference

Gilbert, M. (1988). Logs and laying yards. Shiitake News, 5(1), 8-10.


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