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Growing Mushrooms on Logs

By Marc-Andrew Donsky
Cultivation V

One of the first methods developed for cultivating mushrooms was the cultivation of Shitake mushrooms on logs-the first written record being that of Wu Sang Kwang of the Sung Dynasty of China (960-1127 AD). The advantage of log cultivation is the relative ease of the method and care of the logs, and the life span of the fruiting logs (2-3+ yrs.). The disadvantage is the unpredictability of the method (yield) and the length of time between inoculation and fruiting (6-12 months).

Some mushroom species for which log cultivation techniques are applicable include: Reishi or Ling Chi -Ganoderma lucidum; Maitake or Hen of the Woods-Grifola frondosa; Lion's Mane-Hericium erinaceus; Shitake-Lentinula edodes; Chicken of the Woods-Polyporus (Laetiporus) sulphureus; Oyster Mushrooms-Pleurotus sp.

Log cultivation involves the placement of "plug" spawn into suitable logs. Plug spawn is most conveniently to be found on fluted hardwood dowels. You can produce your own plug spawn by weighing a quantity of dowels into a mason jar; adding an equivalent weight of water; sterilizing as with grain spawn; and inoculating the dowels with mycelium covered agar, grain, or sawdust. If the logs to be inoculated are a different wood than the dowels then 1or 2 grams of the log's wood should be placed with the dowels. Sawdust spawn can also be use to inoculate logs; a special tool called a "sawdust palm inoculator" can be used to facilitate the process.

Hardwoods such as oak, cottonwood and elm are often recommended as standard for log cultivation. Thick-barked hardwoods are preferred over paper-bark woods such as birch. Maple and alder are also frequently seen in the literature. Plum wood is given mention in the cultivation of Reishi Mushrooms. Logs should be cut to lengths of 3-4 feet, three weeks to three months prior to inoculation (plugging). Stumps can also be used. The period of time between cutting the logs and inoculation allows the naturally released anti-fungal (wound compounds) terpenes and (poly) phenols to degrade so that they do not inhibit the colonization of the log by the mushroom mycelium. Logs and stumps can be inoculated any time between last and first frost. Holes, 2 inches deep, of the same diameter as the plugs being used are drilled into the logs, 2-4 inches apart. Stumps are inoculated around their circumference into the sapwood (between the bark and the heartwood). One mycelium-covered dowel per hole is then pounded into each hole in the log or stump.

Holes can be painted with cheese wax or beeswax to protect the mycelium during incubation. The ends of the logs can also be painted with wax if moisture retention is a concern. (Note: in higher temperature climates, such as our own, the wax can melt into the dowel holes and potentially cut of the availability of air to the mycelium. Thus, there is a toss up between the advantages of moisture retention/mycelium protection vs. adequate aeration of the developing mycelium.) After the logs are plugged, they are stacked in a suitable location in crisscross piles called "ricks" for incubation over the next 6-12 months. The rick stacking helps to maintain an even moisture content/environment. The logs can also be covered with tarp (not with plastic) to help conserve moisture. Beds of (and insulation with) sawdust and/or wood chips is a very effective and simple method of environmental control. During incubation, logs should be watered once or perhaps twice a week as required to maintain an optimum humidity.

After 6-12 months of incubation, the logs are checked for mycelia growth by chipping away an area of bark around one of the plugs. If mycelia growth is evident fruiting is initiated by soaking the logs by submerging them in a tub or tank (or watering with a sprinkler) for 24 hours. Chlorinated water should be avoided for fruit initiation although it is acceptable for general watering of your logs. The logs are restacked in an arrangement that allows fruiting from and access to all sides of the logs. Watering is continued 2-3 times a day (2-3 times a week for partially buried logs and stumps) or as required- depending upon the prevailing weather conditions. Mushrooms should begin to form two weeks after initiation. After each flush, allow the logs 2-3 week dormancy period before reinitiating fruiting. This cycle of fruiting and rest can be continued throughout the growing season. Some hardwood logs have been reported to bear fruit for upwards of 3 or more years although the size of the crop decreases each season.

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