The oldest method of mushroom cultivation has stood the test of time and is still the first method many cultivators attempt. However, some people try and fail, or give up hope before their logs have had a chance to fruit. Success with log culture depends on timing, wood selection, spawn quality, and maintaining good conditions for mycelial growth and mushroom development.
Begin by selecting and harvesting good wood. As with sawdust, most wood-loving mushrooms prefer hardwoods without strong antifungal properties. Cut logs from live trees in winter to early spring when the sap has begun to flow and before the leaves unfurl; this is when the wood has the highest level of sugars and bark is tightest. Wood cut at other times will work but will yield fewer mushrooms.
The ideal size for production logs is 4 to 6 inches by 4 feet, though other sizes can work. It’s said that shiitake logs can produce for as many years as the log has inches of diameter. Cut cleanly and avoid decayed wood, abundant branch stubs or damaged bark. Store logs out of direct ground contact. Inoculate logs as soon as possible or up to eight weeks after harvest before other fungi get a head start on the wood.
Two methods predominate for log inoculation.
- Plug spawn is tapped into holes with a mallet, or
- Sawdust spawn is inserted into holes with a funnel and dowel or with a palm inoculator (a specialized tool similar to a potato gun, available from mushroom cultivation suppliers). The palm inoculator is stabbed into the sawdust spawn to fill the chamber then plunged into the holes.
Plugs are more convenient, but I prefer the higher inoculation rates and cheaper materials of the sawdust spawn method.
Drill holes 1 1⁄2 inches deep in a 4-inch diagonal grid pattern over the wood, approximately 4 to 6 staggered rows of 8 to 12 holes. For plugs, use a 5⁄15-inch bit, and for palm or funnel inoculation, use a bit with the same diameter as your tool; mine is 1⁄2 inch. Larger holes are not recommended because spawn may fall out. If you’re going to do a lot of logs, consider buying an auger bit for an angle grinder, which bores holes way faster and easier than a drill. Sanitize hands and tools with alcohol, then get the spawn into the holes, making it flush with the surface of the bark.
Seal the inoculation holes with hot molten beeswax or cheese wax applied with a paintbrush or turkey baster. Sealing keeps out contaminants and fungus-eating invertebrates, and keeps in moisture. Some people wax the cut ends of the logs, too, but this is optional and uses a lot of wax. I use a small slow cooker to melt my wax, though a double boiler or a dedicated pot or tin can on a burner work as well. Logs are labeled with species, strain and inoculation date inscribed on tags that are cut from an aluminum can and tacked on with small nails.
Stack logs tightly in a shady place out of direct ground contact, such as on a pallet. The close quarters promote mycelial growth as well as competitor growth, so after a month or two, restack more openly like a log cabin (crib stack), A-frame, or lean-to to reduce competitor pressure. Monthly watering (or soaking for two hours or less) is beneficial in very hot, dry summers. Sufficient myceliation to support fruitings typically takes six months to two years, depending on spawning rate, species and strain, temperatures, wood type and log size. Mycelium and wood degradation may be visible at the ends. Logs may be a bit lighter than at inoculation.
Judging when logs are ready to fruit usually takes experience, but there are a couple of ways to test.
A drop in pH from 5.5-to-6 to 3.8-to-4 indicates readiness (put 10 grams interior wood into 100 milliliters distilled water and measure pH). One may cut a thin round from the end of a log, moisten it with distilled water and place in a plastic bag. Mycelial growth should be visible within a week if it’s ready to fruit. If climactic conditions are conducive and logs are ready, spontaneous fruitings will let you know.
When left to the weather, myceliated logs will usually give one or two flushes per year. To induce fruiting during warmer months (May to August), logs are soaked in water for 24 hours and restacked upside-down from how they were previously stacked. The inundation of water expels CO2 that has built up in the wood and provides the moisture for mushroom formation. Shiitake logs are further stimulated by a physical shock, like being slammed on the ground just be careful not to overly damage the bark. Logs should be allowed to rest and dry out for about seven weeks after a flush is harvested but can be encouraged to fruit up to three times per warm season.
Growing Mushrooms on Stumps
Stump cultivation is a great laissez-faire approach. Because stumps are still connected to the tree’s roots, they wick moisture up from the ground. Stumps are best inoculated when freshly cut, before a wild mushroom flush in the area sends spores galore onto the cut face.
Stumps are inoculated in the same way as logs, though the cut face is also inoculated, mostly in the nutritious sapwood close to the bark. Gashes or grooves may also be cut into a stump with a (chain) saw and packed with sawdust spawn.
If growing gilled mushrooms on logs or stumps, be sure of your identification in case poisonous lookalikes grow spontaneously. Inoculated logs can be sunken into sand in pots or into ground like posts, imitating a stump-like condition.
The preceding article on mushroom cultivation was excerpted from DIY Mushroom Cultivation: Growing Mushrooms at Home for Food Medicine and Soil by Willoughby Arevalo from New Society Publishers.