Shiitake is cultivated in two ways – outdoors under the forest canopy on natural hardwood logs, or in a climate controlled building on artificial logs made of hardwood sawdust and various nutrients. The advantage of outdoor production is that it involves minimal capital investment, the logs can be cut from your own woodlot or purchased locally, and since they are kept in the bush under a canopy of trees to fruit there is no need of a building. Another advantage is that, in general, a better quality product is produced outdoors even though there is quality degradation if the mushrooms are soaked by heavy rains just before harvest and/or there may be loss due to slugs depending in your location. The disadvantage of outdoor production is that it is seasonal production only, versus year- round production for indoor cultivation, and that outdoor production on hardwood logs entails a heavy physical work load especially if you have large diameter logs.
All mushrooms are actually the “fruits” or reproductive forms of various organisms classified as fungi, they are like the apples on a tree. The actual fungus is a white strand-like mass called mycelium; if you see a mushroom in your forest or lawn you will find the mycelium growing under the surface. Shiitake mycelium is a primary wood decomposer – it degrades the lignin and other components of wood and extracts the nutrients to feed itself. When it has gathered enough resources the mycelium will try to reproduce itself by producing mushrooms, which then release spores into the air. To cultivate this mushroom, mycelium is introduced into the logs in the form of a cloned culture called spawn. Spawn is sawdust that has been colonized with the mushroom/fungus mycelium; it looks white, has a fresh scent, and is almost spongy to the touch. Following this inoculation the logs are placed in an environment that is conducive to mycelial growth – shaded, well ventilated, and well drained. When the mycelium has run through the sapwood and taken over the logs (about a year in Ontario; less in more Southerly locations) we can either stimulate them to fruit or wait for natural fruiting. By keeping our logs in the right environment such as under the forest canopy, the mycelium will continue to stay alive and will degrade the wood until all the nutrients are gone, periodically producing mushrooms during this process. The average or “rule of thumb” lifespan of an oak log is 1 year for every inch of diameter. Other logs may have shorter lifespans depending on how dense the wood is (denser wood takes longer to be digested and used by the mycelium) and the integrity of the bark (when the bark deteriorates and falls off the log will dry out and the mycelium will die).
To start with the logs must be freshly-cut limb wood from a live tree, so there are no competitor fungi already in the wood. Winter cut logs are recommended because there is a high concentration of sugars in the wood which will give the mycelium a kick start, and the bark is very tight on the log. Oak is the best hardwood to use because its tenacious bark will stay on the log for years keeping the moisture inside and the competitors out. Reasonable success, as reported in the literature and as experienced by our own customers, however, has been achieved by using species such as hard maples including sugar maples, ironwood, beech, alder (Pacific coast) and birch, but the longest and most fruitful production is achieved using oak. It is worth noting here that soft woods are not suitable, that fruit woods are notoriously bad, and that walnut is not suitable. Note that we and other growers have not had success with Shiitake on Poplar. Ash has also proven disappointing. Also note that Oyster mushroom (Pleurotus ostreatus) can be successfully cultivated on Poplar.
Once cut the limb wood can be left frozen in the bush and under the forest canopy, off the ground/out of the mud, and/or stacked to allow ventilation around all logs until spring. Logs can be cut into 4 ft. lengths and inoculated with the mycelium – the spawn – as soon as the weather warms up. This is generally late April early May in Ontario. If a heated greenhouse or building is available inoculations can begin earlier. Ideally, the logs range between 4″ to 8″ diameter; large logs can be heavy & unwieldy. However logs as thin as 2-3 inches can be used but should be monitored frequently so the grower can prevent dehydration. Do not allow logs to completely dry out such as in a drought.
Inoculating the mycelium into the logs is accomplished by drilling a series of evenly spaced holes around the perimeter and along the length of the log. Larger diameter logs require more holes. A small quantity of mushroom spawn (sawdust spawn is mycelium that has grown through a sawdust substrate colonizing it completely) is placed into each hole and each hole was sealed with cheese or bees’ wax. In general sawdust spawn is cheaper and works faster than wooden dowel plug spawn. Spawn should be inserted into logs that have a moisture content of at least 25%
Large scale commercial producers, mostly in the Far East, used loose sawdust spawn that was injected into the holes using a manual or pneumatic inoculator. This contrasts with the dowel plug spawn and the sawdust plug spawn which can be pushed into the holes in the logs with your fingers. The dowels must then be hammered in to be flush with the bark and the hole must be sealed with wax. Note that we provide only loose sawdust spawn; we no longer make sawdust spawn plugs.
The logs are then stacked and there are various stacking patterns that can be used. Logs are stacked in the shade/under the forest canopy and are monitored for moisture content. Logs should not be allowed to dry below 25% moisture content or the mycelium will die. Watering the logs once a week (unless there is plenty of rain) by setting up a sprinkler over the stacks is recommended for 3-4 months immediately following inoculation. The sprinklers should be on for 3-4 hours to soak the logs. Although this watering is not absolutely necessary it has been shown to speed up the spawn run process and may result in some mushrooms in the autumn provided the inoculation was done in early spring. It has to be noted that this watering regime of 3-4 hours/day is only for the spawn run/incubation period; it is a short-term strategy to prevent logs from drying out if drought conditions prevail and is NOT to be continued or practiced once logs begin to yield/fruit. The log watering regime for ‘producing’ logs is by SOAKING by either immersing or sprinkling for 24 hours continuous. Following soaking the logs should be allowed to stand in a well-ventilated and shady area. You do not want the bark of the log to remain wet as this will encourage the growth of molds on the surface of the log and may result in de-barking. Log should yield after soaking and then must rest for 8 weeks before soaking (forcing) again. It bears repeating that continual watering for short time periods will lead to slime molds developing on the bark and the bark will deteriorate and fall off. Once the bark is damaged or falls off the log the interior of the log will dry out and the mycelium will die.
As the spawn run proceeds the mycelium will colonize the sapwood of the log and you will be able to see white mycelium at the ends of the log in a ring. By the following spring/summer mushrooms will start to pop out from the sides of the logs. At this time the logs are rearranged so that they are standing up. Various arrangements for standing are used – this can be accomplished by stringing wire between trees or posts and leaning the logs alternatively on both sides. This allows the mushrooms to come out without touching the ground and allows easy picking from all around each log. Moving and rearranging logs during watering or at other times (dropping the log to the ground) contributes to the initiation of fruiting since Fungi reproduce in response to catastrophe (such as a tree falling or a lightning strike or torrential rain).
LOG MANAGEMENT: The mycelium will ‘run’ through the sapwood and take over completely in 6 months to 1 year. The triggers that produces mushrooms are moisture and temperature. Heavy rains will stimulate Shiitake logs to produce in both the spring and fall. But rather than wait for natural rainfall you can “force” the logs to produce by either soaking (immersing) them in cold water for about 12 hours or by setting up a sprinkler system on them continuously for 24- 48 hours. SOAKING is required – NOT intermittent sprinkling. Water must get right into the center of the log. It must be noted here that soaking does NOT mean intermittent sprinkling – it means continuous soaking for 24 hours. Following the soaking the logs must be allowed full ventilation so that the outside of the log is able to dry out; if the outside of the bark is continually wet or re-wetted it will be vulnerable to slime molds that will rot the bark off the log and cause the log to dry out and the mycelium to die.
Depending on the ambient temperature, mushrooms will start to form 1-2 weeks after soaking and will be ready to pick a few days after that. In the cooler spring or late fall weather the mushrooms grow slowly producing a dense fleshed product which is considered to be the best quality. Summer growth is much faster producing a thinner fleshed mushroom. Once the “flush” of mushrooms has been picked the logs are left to rest for eight weeks and then can be soaked again for another crop. Three to four flushes can be forced from April to December depending on geographical location. Farmers with heated greenhouses can bring the logs inside and produce during the winter as well. It must be noted here that the more the log is forced to fruit the shorter will be its life span; the wood will be digested more quickly. When this has occurred the log will become ‘punky’ and at this point it should be culled from your production line and burned or composted.
The average yearly production will be 1-2 lbs. per log or perhaps more if the logs are forced more often. However this will shorten the overall lifespan of the log but will likely produce the same quantity of mushrooms over the life of the log. The total average yield from one log will be in the neighborhood of 8 lbs. with proper management techniques.
For more information contact us