Take a freshly chopped (2-6 week old) and disease free log of minimum 10cm and maximum 35cm diameter and up to 1m length from a deciduous tree.
These trees are preferred as they store sugars more readily in the wood providing better nutrients for growth.
It needs to be freshly chopped wood of a healthy tree, as you want the log to be completely free of infection by other funguses at the time of inserting the plugs.
Also an older tree may have begun to dry out or lost some of its bark which will make it less suitable for mushroom cultivation. To check the tree for health look for other funguses, unusual growths or large dead sections and branches.
It is good to wait 2 weeks after chopping so that the natural defence of the tree against fungus has broken down. Soft woods like poplar will be infected by other funguses very quickly, especially in summer or spring, when the wood is very wet and the ambient temperature is rather elevated. Don’t leave them laying around for too long if you can avoid it. Harder woods like oak or beech are less of a worry if they can stay on the floor for a few months before inoculation.
Wood which contains a lot of resin or tannin or oil is not suited for inoculation: no conifers, eucalypts, oleanders, nor tropical hardwoods! An ideal log is 10 to 20 cm in diameter for ease of handling, as larger logs can be difficult to move without the risk of injury.
Wide logs and tree trunk sections 30cm to 100cm in diameter can be cut into rounds that are 30 cm deep. Tree stumps should be cut at ground level or up to 100 cm above ground level and between 20 and 100cm in diameter.
After selecting your wood, remove extra branches to leave just the main log for inoculating. At this stage, you could also pressure wash the log to remove any moss etc.
Take extra care not to remove or damage the bark. If the log is a moisture reserve for your mushrooms, then the bark is the skin that maintains it at the right levels.
For the 2 week seasoning period it should be stored off the ground and out of wind and direct sunlight to avoid drying out.
Following that, it is beneficial to soak your logs overnight in untreated water (Figure 1) so that they are well saturated. A tell-tale sign that the log is becoming too dry are cracked ends and peeling away of the bark.
Drill holes in rows along the log, about 10-15 cm apart, of the same diameter as the plugs (8mm) and a little bit deeper than the length of the plug (usually 4cm). If you do not have a depth collar it is a good idea to mark the drill bit to ensure correct depth. As you move to a fresh row it should be lined up with the centre of the previous row to produce a diamond shape (Figure 2). There is no need to drill into the ends of the log.
The amount of inoculation points depends on the type of wood you use, on the thickness of the logs and on your incubation variables. Harder wood, thicker logs, colder temperatures = more closely spaced inoculation points.
Common plug rates are outlined below. If you wish to increase the speed at which the mycelium colonises (the inoculation rate) or you are dealing with a particularly thick piece of wood this can be increased proportionally.
For logs: 40 plugs are recommended for every 50cm in length with a diameter of up to 20 cm. For larger diameter logs up to 30 cm in width, 50 plugs are required per 50 cm length.
For rounds and Stumps: 40 plugs are recommended for rounds and stumps up to 30cm in diameter with a depth of 30 cm. For every additional 30 cm in diameter, an additional 40 plugs are required. There is no need to drill into both sides.
In order to calculate distance between rows:
1. Measure the circumference and then minus 5
2. Divide this by 6 (for logs up to 20cm diameter) or 8 (for logs above 20cm diameter)
3. The final number is the distance between your rows.
For a log that is <50cm start 2.5cm from the cut on each end. For a log, 50cm-1m start 5cm from the cut on each end.