Cultivation methods: wood-inhabiting mushrooms

Woody materials and logs can be prepared much more quickly than compost. The logs should be cut from healthy trees (preferably due to storm damage or tree maintenance work) during the dormant season. The mushrooms feed on the cellulose and lignin in wood, and once the log is fully occupied by the mycelium, it will produce the fruiting bodies. Trees with heavy, dense wood (including most hardwood tree species) encourage the mushroom mycelium to develop well and allow it to produce mushrooms for longer; conifers (pines and other softwood) should be avoided.

The harvested logs should be six to eight inches in diameter and cut into three foot sections for ease of handling; smaller diameter logs dry out too quickly and larger logs are harder to handle, and take longer to colonise. The logs used must be free of scars, damaged bark and have as few  branches as possible – this will reduce the possibility of other fungi invading and the logs to lose moisture; branches should be cut flush with the log surface and sealed with wax during the inoculation process. A log only needs to be inoculated once; the mycelium grows through the log decomposing it. Logs should be inoculated within one month of being harvested.

The techniques for inoculating logs include:

• Drilling into logs – drill into the log to a depth and diameter in excess of the dowel size, then insert the dowel and seal with wax. The holes should be spaced about ten inches apart, with approximately six inches between rows; it is best if adjacent rows are offset, so the holes form a diamond pattern. To ensure that the mushroom is established quickly, twenty to twenty five dowels should be used for each log.

• Sawing a wood disk – cut a three to five cm thick disk, then deposit the grain spawn in the middle area (the cut surface) of the remaining log and seal with wax along the outer margin; secure the disk by nailing to the remaining log, covering the spawn and wax layer. To ensure that the mushroom is established quickly, it is essential to combine the wood disk with as many wedge cuts (see below) as possible in the same log. Cover the inoculated zone with polythene sheeting.

• Sawing a wood wedge – cut out a wedge about three to four cm deep, then deposit the grain spawn in the middle area (the cut surface) of the remaining log and seal with wax along  the outer margin; secure the wedge by nailing to the remaining log, covering the spawn and wax layer. Cover the inoculated zone with polythene sheeting.

• Sawing several slits – cut a few slits up to five mm wide and three to five cm deep along the log, then deposit the grain spawn in the slits and seal with wax. To ensure that the mushroom is established quickly, it is essential to combine the slits with a disk and wedge cut (as many as possible) in the same log. Cover the inoculated zone with polythene sheeting.

In order for the mycelium to colonise the log, spread and produce fruiting bodies, the inoculated logs should be stored in a cool, moist location. In most cases, the logs should be stored under existing trees and shrubs (70% shade) and sheltered from the wind. There should be sufficient space to stack logs and the location is accessible enough to facilitate maintenance and harvesting. The logs must be stacked in a manner that promotes air circulation; do not place the logs flat on the ground. The moisture content of the logs should be monitored – they need to be kept moist because the mushroom will die if the logs dry out. Depending upon the type of mushroom being cultivated, the species of logs used and weather conditions, it will take from six to eighteen months for a mushroom to colonise the log and produce fruiting bodies.

Hormone changes in the mycelium stimulate fruiting bodies to form; mushrooms respond to environmental stress and under natural conditions, this occurs after a heavy rain or a reduction in temperature. Humidity and log moisture levels must be maintained. Mushroom development can be promoted by soaking the logs – the soaking time varies, depending on air temperature and may require six to twenty four hours in the summer but up to two days in the spring or autumn. Depending on the type of mushroom and species of tree used, a log should continue to produce fruiting bodies for two or three years.