WSU Extension > Working Riparian Lands Program > Forest Farming > Forest Farming Crops > Forest Cultivated Shiitake Mushrooms

Forest Cultivated Shiitake Mushrooms

Background

Forest cultivated shiitake is an agroforestry practice that can reliably produce high-quality shiitake mushrooms in a forest using logs as substrate.  This method has been developed over 1,000 years in Japan and China, where shiitake is a native species.  In the 1980’s, this method was adapted to the eastern U.S., where shiitake is not native. This practice is low risk, requires minimal space and equipment, and yields a high-value mushroom that is ideal for direct-to-market sales to restaurants, at farmer’s markets, or as supplement to a CSA.  It utilizes small-diameter hardwood logs as substrate, which makes it compatible with forest enhancement practices like thinning.  Today, most shiitakes are produced using bags of sterilized sawdust in climate-controlled facilities.  However, log-grown shiitakes still provide an opportunity for farm and forest owners to diversify and supplement their income.  

There are fewer forest cultivated shiitake producers in the Pacific Northwest, largely due to a lack of research and guidance available to support the adoption of the practice to the unique climate and hardwood species in the region.  However, WSU Extension began researching this in 2019 and is actively developing best practices for commercial-scale and hobbyist shiitake cultivation in Washington State (see below for details).

A perfectly ripe shiitake mushroom grows from a red alder log beneath a forest canopy.

Overview

Cultivating shiitake on logs is a relatively simple process but it does require time.  Small diameter hardwood trees (e.g. red alder) are felled in the late winter to provide fresh substrate (downed wood collected from the forest floor won’t work).  Those trees are cut into four-foot lengths (called “bolts”) in the spring and then “inoculated” by drilling holes in them, filling the holes with shiitake spawn, and then covering them with wax.  The bolts are then moved to the forest where they will have sufficient shade for the spawn run, which is the period required for the shiitake to fully colonize the log.  This is typically a full year from the time of inoculation, after which the bolts can be forced to fruit by soaking them in cold water for 24 hours.  Bolts can be force fruited 2-3 times per year for multiple years, before the carbon and nutrients in the log are spent.

A graphic describing the timeline for forest cultivated shiitake.
It takes time for the shiitake fungus to colonize a log before you will be able to harvest any mushrooms, but the log will produce for several years afterwards. Graphic by Eric Jones, OSU.

A small-scale commercial system would likely start at 100-200 logs while larger operations will have several hundred to 1,000+.  Much of the labor for this process occurs during inoculation, but most commercial operations will add new logs every year to maintain yields.  Some specialized equipment and supplies are necessary, including a modified angle grinder, inoculation plungers, and shiitake spawn, but farmers will often have much of the other necessary equipment already (e.g. chainsaw, sawbuck, t-posts).  Livestock tanks are often the most expensive investment, which are used to soak the shiitake logs and force fruiting. 

A red alder forest.
Fresh, small-diameter trees must be felled to ensure that the logs have sufficient moisture for fungal growth and no other fungi have been established. Red alder is a good substrate and it often grows in dense stands that can benefit from thinning.
A stack of four-foot logs ready to be inoculated with shiitake spawn.
Logs are then cut into four-foot “bolts” and transported from the forest to a covered area with electricity for the inoculation process.
An inoculation station consisting of a table with caster wheels fixed to it to hold the log, a bucket of spawn, and a hot plate with melted wax.
The inoculation process includes drilling evenly spaced holes, filling with sawdust spawn, and covering with wax to seal in the moisture. Simple upgrades can help the process go more quickly, such as fixing caster wheels onto a table so that the log can be easily rolled.
Logs arranged in "cribstacks" by criss-crossing them in stacks in the forest where they will have sufficient shade.
After inoculation, bolts are taken to the forest and arranged in “crib stacks” for the spawn run, which takes 12-18 months. The area where the bolts are held is called the “lay yard” and should have full shade, protection from wind, and a mix of hardwood and conifer cover. The bolts will stay in this area for the remainder of their lifespan.
Shiitake logs immersed in water in livestock tanks being held down by two by fours.
Shiitake can reliably be “force fruited” by soaking it in cold water for 24 hours, which makes it ideal for commercial production. Soaking also helps put moisture back in the logs to ensure successful colonization and maintain yields.
Shiitake bolts standing upright in an "A-frame" for harvest.
After soaking, the bolts are stood upright to allow for mushroom growth and easier harvest. During this time, covering with a breathable fabric, such as a fruiting blanket, will protect mushrooms from pests and produce a higher quality mushroom.
Shiitake mushrooms growing on logs from below.
Shiitakes are typically ready for harvest 5-7 days after soaking, depending on weather conditions. Mushrooms can be cut from the logs using a knife or scissors and stored in a breathable container in the fridge for up to a month. Bolts can be soaked every 7-8 weeks, usually resulting in three harvests per summer.

Local Research and Guidance

Since 2019, Washington State University Extension has been managing log-grown shiitake trials in Western Washington.  These trials have revealed key management guidance around choosing tree species for substrate, shiitake spawn selection, and how to mitigate the negative effects our low-humidity summers have on successful colonization and yields. 

Considerations for Riparian Buffers

Forest cultivated shiitake systems have a very low ecological footprint and require minimal space, making it an ideal practice to incorporate into a riparian buffer.  The higher relative humidity in riparian areas can even benefit moisture retention in the shiitake bolts.  The bolts will benefit from a mix of hardwood and conifer shade, which may or may not be available to you if working within an existing forested buffer.  You will also need to have access to water wherever you keep your bolts (called the “lay yard”) for soaking.  If you don’t have access to a well in that location and don’t have water rights to draw from a nearby water source, soaking the bolts in a cold stream can work, provided there is a 20-30 degree difference between the water and air temperature.  However, yields will likely be reduced because it is difficult to fully immerse logs in this situation.  It’s also important to consider potential restrictions on harvesting trees for substrate in riparian buffers, particularly in the inner zone.

Shiitake logs standing up right in an alder forest with a river in the background.

Guides and Resources

Most of the available guidance on shiitake cultivation in the United States has been generated in eastern states.  Although the principles are the same, the WSU Extension trials have determined some critical supplemental guidance to ensure successful shiitake production in the Pacific Northwest.  We recommend using the Pacific Northwest Forest-Cultivated Mushroom Growers Network and other regional guides as your primary resources, while using non-regional resources as supplemental guidance.

Pacific Northwest Forest Cultivated Shiitake Resources

Other Forest Cultivated Shiitake Resources

Shiitake Spawn and Equipment Suppliers

Relevant Forest Management Resources