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When is the best time to plug logs, and other nitty-gritty on mushroom log cultivation

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The best time of the year to plug logs, at least here in East Tennessee, is February and March because of the weather and the sap run. Logs we have plugged this time of year have produced mushrooms in 4-5 months. However we have had success plugging logs all year just as long as logs are recently cut (within the month) from a disease free tree.

With careful management, each log should produce around 2 pounds of mushrooms over its lifetime, but uncontrollable factors such as wind, temperature and humidity will effect yields. Expect mushrooms within one year, total productive life of log can be 4-6 years.

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Weather: February and March typical average temperatures of 50°F will support mycelium growth while keeping in check the growth of other organisms. Competing organisms like bacteria prefer higher temperatures (Oei, 2003). Even if the temperatures plummet the cold won't kill the mycelium. They won't be actively growing below 32°F, but they won't die back. In addition, the high incidence of rainfall during the late winter and spring is key for keeping the mycelium happy and growing.

Sap: In the fall, life essential juices are sucked from the leaves and shipped to the roots for winter storage. In the late winter and early spring the roots return nutrients up to the tops of the trees to facilitate the production of new leaves. These readily available sugars and minerals will feed happy mushroom mycelium.

Logs: Use recently cut hardwood logs (white oak, red oak, poplar, maple, birch, beech, etc.) 4-6 inches in diameter and 2-3 feet in length. The logs can be bigger, it is what you feel comfortable moving around, especially if you plan to soak logs every few months. Avoid evergreen hardwoods (magnolia), evergreen conifers (fir, cedar, pine, etc.) and walnut, black locust and cherry.

Don't use logs that have been outside for longer than a month, or those with excessive damage to the bark. Logs that have been outside for sometime are likely to be colonized with a native fungus. Bark damage will inhibit mushroom growth due to water loss. 

A few mushrooms, including Phoenix oyster, will grow on evergreen logs. All the same avoid strong smelling evergreens like Cedar; the strong smelling compounds (think turpentine) are designed to fight off potential pathogens like mushroom fungus.

Plugs are small wooden dowels colonized with mycelium, the mushroom’s “root” network. Available in a wide variety of species, plugs are raised in sterile, temperature- and humidity-controlled conditions to ensure their viability. For novices we recommend shiitake plugs, these grow best on white and red oak but can be grown on most hardwoods.

Inoculating logs: Drill holes with a 5/16th drill bit, spaced 4-5 inches apart and 1+ inch deep along the log, add staggered rows 1-2 inches apart. Inoculate near branching twigs and add extra holes about one inch from ends of the log to establish a strong spawn run where contamination is most likely to enter. Hammer plugs into holes to be flush with the surface. Cover holes with melted cheese wax to protect plugs and keep them from drying out. Some growers also elect to cover the exposed ends of the logs with wax, but this may not be necessary.

Alternatively you can also counter sink the plugs with a punch. This allows for a nice wax reservoir. The purpose of leaving the plugs flush allows for maximum contact with the active vascular tissue. The active phloem is the dark layer right under the bark and the xylum layer is under that, this is where the sap and nutrients are shuttled to bring nutrients to living cells in the tree.

Temporary laying: After inoculation logs should be stacked like firewood on a hard surface where it is shady and receives precipitation. Stacking in a close horizontal pile keeps the humidity at the log surface. If you live in an area with low humidity/precipitation logs can be watered and covered with plastic to keep humidity high. After 1 to 2 months logs should be separated so that mold won't move in and take over.

Permanent laying: Find a shaded, damp area sheltered from the wind. The log will need to receive rainfall unless you are regularly soaking it. A north-facing wall out of the wind is a good place, alternatively under a shady tree. Slugs can also be a problem - you may need to bring the log in to a slug free area while it is fruiting. The most important thing is to put the log somewhere easy to see! Log cultivation requires patience and mushrooms appear suddenly without warning so the easier it is to check on them the better.

Stack logs in a lean to or log cabin style so that air can freely circulate over most of the surface of the logs. Logs should not be in contact with the bare ground where competing fungi lurk waiting to move in on your yummy log. Pavers or bricks work well as barriers.

Logs should be kept in a shady area where precipitation is not impeded. Excessive drying of logs should be avoided, I tell folks who come into our store that if we have a drought for a few weeks and you are watering your perennial plants, then it is a good idea to soak you logs. 

If you are so lucky to have access to a stream or the entrance of a cave, these are great places to keep mushroom logs.

Initiating flush: When the spawn run is complete, the logs are ready to fruit. Shock the logs to initiate fruiting by knocking one end of the log sharply on hard ground and totally immersing it in cool or cold water for 24-48 hours. The water should be non-chlorinated, rainwater or tap water left to stand overnight. Place the log in a sheltered, shady spot and lightly cover with plastic to increase humidity. Logs should start fruiting within 1 - 3 weeks, forming in 'flushes'. Remove the plastic cover once fruiting has started.

Cut the mushrooms off the log when the cap is 3 - 4 inches across, after 4 - 8 days of growing (they'll grow quicker in warmer temperatures). It's important to cut them off the log rather than picking them - this could reduce the chances for more mushrooms. Trim off the tough stalks before cooking and eating.

Resting Logs: After picking the mushrooms leave the log outside in a damp place for four to six weeks to rest, then soak the log to start the second fruiting flush. Frost and snow are no problem. This resting period is for the mycelium to extract more nutrients from the log for more shiitake mushrooms.

Whims of Nature Log Cultivation: It is also possible to simply leave the log outside in a shady place and it will fruit when the outside temperature is warm and wet. This is the easiest way of growing mushrooms, but not so productive and predictable! The log should fruit for up to six years. During periods of prolonged dryness or drought, periodic overnight soaking may be needed.

Log Invaders: While some competitors will diminish or overtake your edible mushroom harvest other organisms can live in harmony and your log will produce normal crops. Some of the “harmonious invaders” are actually indicators that the environmental conditions for mushroom growth are favorable. A couple positive indicators are the little black jelly like cup fungi Black Bulgar (Bulgari iniquans) and the scaly light green/white Lichens. While being a positive indicator of environmental conditions the striped turkey tail polypore (Trametes versicolor) will diminish or overtake your intended crop. On the positive side turkey tails is a chewy edible that has well documented medicinal qualities including enhancement of the immune system. The forest-green fungus Trichoderma or Diatrype stigma, a pearly-gray turning-to-black bark-blowoff disease, often appear when logs are too wet and there is poor air circulation. Logs that show signs of Trichoderma or Diatrype should be removed from your mushroom log stack immediately and cleaned with rubbing alcohol.

Have no fear, Black Bulgar and Lichens appear on your logs

Reference

Oei, P. Mushroom Cultivation: Appropriate Technology for Mushroom Growers. Mushroom Cultivation: Appropriate Technology for Mushroom Growers. edited by P. Oei 2003.

originally posted February 19, 2013