Harvesting Shiitake: Forcing, Soaking and Resting Logs

Shiitake logs fruit when the weather triggers them, or when you force them by soaking in cold water. Soak for 12 to 24 hours (Cornell) or 24 hours (Cornell’s forcing page and the University of Wisconsin), wait 3 to 5 days for pins, pick when the caps are about two-thirds open, then rest the log for 6 to 8 weeks. This page covers the harvest end of the shiitake growing guide once your logs have finished incubating.

When to force a log

Cornell calls soaking “shocking” or “forcing”. It is a way to induce fruiting rather than waiting for rain. The timing rule is that night-time temperatures should average above 50°F before logs are shocked. Cornell also found that growers who waited longer before the first shock got significantly greater production, so do not rush a young log. Our sources give 6 to 18 months of incubation before a log is ready.

The soak

1. Submerge the logs in cold water. Cornell says to submerge the logs for 24 hours on its forcing page, and describes shocking as soaking in cold water for 12 to 24 hours on its basics page. The University of Wisconsin says a 24-hour soak will stimulate mushrooms even more.
2. Know your wood. Cornell notes that oak and sugar maple take up water more slowly than hornbeam, so the species you cut affects how a soak behaves.
3. Wait for pins. After soaking, the log will begin pinning in 3 to 5 days. Look for bumps about the size of a pencil eraser.
4. Protect the pins. Try to protect budding mushrooms from rain storms, particularly 2 to 3 days before picking.

Where the sources differ

The soak length is the clearest conflict. Cornell’s basics page says 12 to 24 hours, its forcing page says 24, and Wisconsin says 24 stimulates more. They do not contradict so much as widen the range: 24 hours is the figure all three allow. Cornell’s forcing text also notes shorter soaks in warm weather, but does not give a number we can quote.

Humidity and light on a fruiting log

Our sources give no humidity percentage for shiitake. One Cornell grower quote explains that the purpose of an agricultural-cloth fruiting cover is to keep the humidity consistent during pinning and fruiting. Clear tarps, by contrast, create a greenhouse-style effect on mushroom caps and should be used with caution depending on direct sunlight and outdoor temperatures.

When to pick

Maryland Extension says to harvest when caps are about two-thirds open. Cornell describes pins as pencil-eraser bumps, and our sources do not give a size or a day count for the final stage, so judge by the cap.

Resting and flush timing

After fruiting, Cornell says logs need to be rested for 6 to 8 weeks before being forced again. A log fruits biannually for three to four years, at upwards of 8 ounces of mushrooms per flush (Cornell). Maryland puts production at about three to five years. A Cornell trial recorded average log yields of 0.5 to 2.3 pounds, with the strain LE-46 performing best.

Pests and competition

Cornell lists slugs, chipmunks and pleasing fungus beetles as pests of shiitake pins. A grower quoted there says chipmunks can take a whole bunch of shiitake pins in fall in a few days, and that without protection they would lose perhaps 4 to 5 pounds of shiitake each week to slugs. How much competitive fungi exist in the log also affects flush size. For other fungus problems, see our contamination guide.

Storing fresh shiitake

Maryland Extension says mushrooms may be stored in a cardboard box for up to a month at 36–41°F. We do not have a sourced figure for freezing or drying.

What our sources do not tell you

We found no humidity figure, no fresh-air guidance and no cap-size guide for shiitake. The soak figures come from Cornell’s commercial guides and a Wisconsin home guide, and neither names a warm-weather soak time. For a faster crop with a different species, oyster mushroom harvesting runs on a weeks-long cycle instead of months.