Published by City Farmer, Canada's Office of Urban Agriculture

Growing Shiitake and Oyster Mushrooms on Logs

Written by Western Biologicals Ltd
March 2009

Producing nutritious, delicious Shiitake mushrooms from "waste" wood that might otherwise be bulldozed and burned as sites are cleared for development, is an appealing concept. A "typical"4" diameter x 40" long Alder log should produce ½-1 lb. mushrooms each spring and fall for approximately 3 years. At $10/lb retail, this corresponds to a gross return of about $50 over the life of the log

Although the labour input is substantial, other costs can be minimal. Spawn and sealant will cost in the neighbourhood of a couple of dollars per log. If logs are harvested from ones own property and inoculated, without outside labour then that cost might be considered zero.

In south-western B.C. Red Alder is considered the best species for Shiitake production. Other species such Oak, Maple, Birch, Aspen may be used, although with lower yields and management tailored to the specific requirements of that wood type.

The following figures are taken from "Growing Shiitake Mushrooms in a Continental Climate" by Kozak and Krawczyk: A 1000-1500 log operation produces approx. 30-50 LB per week year ‘round. At $6. per LB, that is equal to approx. $10,000 net per year. This analysis presumes using little outside labour, little equipment, and pre-existing building.

LOGS: Should be cut green from healthy trees. 4-8" diameter x 3-4' long is considered optimal. Small logs have high surface/volume ratio, and moisture management is difficult. Large logs are heavy to handle and may have a high proportion of heartwood which contributes little to the mushroom's nutrition. The integrity of the bark is very important in limiting moisture loss and excluding contaminants. Logs with a thick ring of sapwood are preferred. Logs should be cut after the leaves have begun to drop in the fall and before the buds break in the spring. During this period nutrient reserves in the sapwood are highest, and the bark is most tightly attached to the wood.

INOCULATION: Drill holes 1/8-1/4” deeper than the length of the plug if using dowel plug spawn, and a diameter so that the plug fits just snugly - 21/64” for WBL dowel plugs in 2009

For sawdust spawn, holes should be approximately the depth of the sapwood (usually 1-1/2"). Hole diameter to allow easy filling with spawn (usually 7/16-5/8"). Other sawdust methods include: saw-kerf method, and butt-end inoculation for large logs.

There are other techniques such as “hammer and chip” and “saw-cut and wafer-spawn” methods. If you are working with more than a few logs, consider getting some help - 2 people working very efficiently can do about 100 logs in a long day. Sawdust spawn is faster growing than dowels, but takes more time and effort to put into logs. Sawdust spawn dries out easily so it must be sealed over. It is appropriate to use dowel plug spawn for small numbers of logs and to use sawdust spawn for more than a few dozen logs. Inoculate as soon after felling as possible. Spawn needs a chance to grow before steady freezing sets in. Spawn will show white under the wax a couple of weeks after inoculation, and may grow up to 1" per week through the wood under ideal conditions (rarely in practice). The mycelium may show white on the bottom end of log after a few months but not if the end of the log is very dry

SEALING: Waxing reduces moisture loss, and protects spawn from contamination as well as birds and insects. Heat the wax to the point it begins to smoke but be careful as it is flammable at that temp. A deep fat fryer works well. Use a baster with "nail valve" for flow control. Cheese wax is good, but plain paraffin with or without addition of mineral oil or beeswax is fine. Wate-base “Seal and Heal” is convenient to use and works well. Do NOT wax or seal the ends of logs.

LOG MOISTURE: Just before inoculation, test 5 logs per 100, selected from throughout the total so as to get good representation of the true log moisture. Cut 6" off end of a selected log, then cut a fresh 1" slab for testing. Weigh the fresh slab immediately and place in a 175-200oF oven for at least overnight. Weigh once and put back in the oven to check that it has dried to "constant weight."

%Log Moisture Content (LMC) =(WetWt-DryWt x 100%) /WetWt

For example, a slab of Red Alder log, fresh cut in March/98, weighed 594 grams “wet” and 299 gm after drying at 200oF for 3 days

LMC = (594-299)/594 x 100% = 50%

Calculated Oven Dry Wt = log fresh wt - (LMC x log fresh wt.) /100 (CODW) Write this, on each log tested, using a permanent label. With this information you can at any time determine the LMC merely by weighing the test logs and doing some simple arithmetic. That is, it is not necessary to sacrifice more logs after the first determination of CODW. Spawn run best if LMC is over 35% 31% LMC is too dry, and the spawn should be considered dead if LMC less than 23%

TEMPERATURE: 75oF theoretically for the fastest spawn run for Shiitake (85oF for Oyster), but logs are more susceptible to Hypoxylon and other disease at warm temps.(over about 75oF), as well as to problems with moisture management. The lethal temperature for Shiitake mycelium is not much above body temp.(100oF) so if a log feels warm to the wrist then at least the surface is too hot. Lethal temperatures can occur in logs exposed to direct mid-day sun in less than an hour even during cool weather.

LAYING YARD: Should be close to water, since logs will usually need to be watered in summer. The site should be accessible and the lay-out of the yard should allow convenient access to the logs and facilities. There must be shading, at least in the summer. 60-80% shade cloth is recommended. Pine forest provides an ideal degree of shading, and air movement. Hill tops are likely to be too windy and drying, while a valley bottom may be a frost pocket, and have stagnant air which may result in increased contaminant problems because the log surface doesn't dry out for long periods. Slugs are a problem and may eat the mushroom“pins” as fast as they appear.

PILING LOGS: A "dead pile" (logs piled like cord wood) is not good due to rain shadow for the lower logs, poor air movement between logs, etc. "A frame" pile is not space efficient. "Crib stack" has rain shadow problem, uneven drying on top. "Lean-to" is best. The lean-to pile can run a long distance with the lower ends of the logs on the ground and the upper ends 8-12" off ground. Stagger between the rows to eliminate rain shadow. The cross pieces may be removed and the logs laid flat on ground in very dry weather. Rotate logs to get a more uniform spawn run.

FRUITING : Requires 35-60% LMC. Growth to full size will take 1-2 weeks from pin set at 65oF, and 2-3 weeks at 45oF

SOAKING: Logs may be immersed in water to stimulate out of season fruiting, but consider oxygen solubility is low in warm water and mycelium may be suffocated by prolonged immersion in warm water. LMC must be greater than 35%, at the lowest, for fruiting. Immerse less than 6 hrs in water at 68oF, up to 2 days in water at 40oF. Stack the logs for access to the mushrooms, usually nearly vertical at this time. Forced fruiting out of season by soaking but there should be 8-12 weeks resting between each fruiting. Forced fruiting will shorten the life of logs.

STRAINS: Cool weather strains fruit at about 50oF, good quality but slower to develop. Mid-temp. strains are more popular and the timing of fruiting may be manipulated by handling technique (water, temp., mechanical shock, etc.)

PROBLEMS: The occurrence of specific problems will vary with the local climate and environment and the species of logs used. However in the mild, wet Pacific Northwest, the following are most common:

- logs don’t dry out enough to kill the living wood so initial colonization is slow. Consider keeping your logs indoors (say in a garden shed, garage or unheated basement) for a few months after inoculation. The logs will quickly dry out enough to kill the living wood and allow for rapid initial colonization and protection from extreme cold will allow the mycelium to continue growing even when outdoor temps are cold.

- leaving logs out in mid-day summer sun will quickly ruin your logs by over-heating them - very quickly, possibly within an hour!

- logs let to dry out too much - this is especially important during the warm, dry months of July and August - although it may be humid there, very little rain makes it through the foliage of large Fir or Hemlock trees. so logs placed there may become too dry over time. - if you are inoculating more than a few logs, then take the time to determine LMC as explained previously. Having an accurate, objective measure of log moisture will facilitate good results.

- logs don’t get enough moisture during fruiting season – it will be beneficial to soak them in a tub or by standing in a poly garbage can full of water, or with a sprinkler. In wet climates the ends of logs may become “sealed” with slime. Logs will take up water more efficiently if slime-covered ends are shaved off with a chain saw or other tool before the logs are soaked.

- Wrapping logs in poly or other wise interfering with the free flow of air around them in any way that allows the bark to remain continually damp will promote the growth of competitor fungi. Some of these are competitors with your mushrooms for log nutrients and some are actually pathogenic to the mushrooms.

- Cedar tree foliage seems to leach inhibitory material onto logs placed beneath them

- keeping log surfaces constantly wet such as by placing the ends in a creek or covering with a tarp may encourage molds and pests especially in warm weather

- Slugs can eat the developing mushroom “pins” so fast that you may think no mushrooms are growing, it is necessary to control slugs. You might pick slugs off your logs at night and use some sort of slug bait. Copper strips may be an effective barrier but do not put copper directly on your logs.

- many problems stem from human failings. Don’t think mushrooms less demanding than other crops. Set up your logs so that it will be easy to monitor and maintain their needs – easily accessible and near a convenient water supply. Consider investing in a piece of shade cloth and building a frame to support it. A clean concrete surface will discourage slugs and insects that lurk in soil. Always use some form of slug bait or effective deterrent.

- holes too small or too large for dowels may damage the living mycelium or allow sealant down around the spawn/plug, allow access to mold spores and insects, or allow the spawn to dry out, similarly if the surface of sawdust spawn is rough and fissured.

- logs cut from trees in a decadent forest with abundant fungi growing on dead and dying trees, are more likely to develop contaminant fungi after inoculation than are logs cut from trees which are young, healthy and standing alone.

- natural rainfall in Spring and Fall is often not heavy enough to promote very heavy fruiting, additional watering/soaking will likely be beneficial.

- spawning “lightly” to save on initial cost may be false economy because the longer the spawn run takes to complete, the more opportunity competitor fungi and insects will have to invade the log, and the longer the log life cycle the more opportunity for mistakes in log management -

Recommended references available from Western Biologicals Ltd: Growing Shiitake Mushrooms in a Continental Climate by M.Kozak and J.Krawczyk Mushroom Cultivation by Peter Oei The Shiitake Growers' Handbook by P.Przybylowicz and J.Donoghue The Mushroom Cultivator by P.Stamets and J.Chilton Shiitake Sampler (Cookbook) by Janet Bratkovitch The Edible Mushroom (Cookbook) by Margaret Leibenstein

SEAL AND HEAL GRAFTING SEAL Keep tightly closed, keep from freezing and store at room temperature. Stir/shake well before using and apply with a small paint brush. Add a small amount of water if it is too thick to work with. Seal and heal requires several hours at a temperature over 10oC protected from rain, to set before it will withstand rain and freezing. It is very much like latex paint except without added microbicides. Because it is a water base material it will tend to soak into the spawn if the surface of the spawn is very wet. For this reason it is a good idea to let the surface of the spawn dry out for a few minutes before sealing it over with Seal and Heal. Clean brush with warm water before it dries.

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Feb 19, 2013

Published by City Farmer
Canada's Office of Urban Agriculture