OWA logo

You are here:Home»Publications»Featured Articles / News»Cultivate Gourmet Mushrooms on Hardwood Logs Outdoors Under the Forest Canopy

Cultivate Gourmet Mushrooms on Hardwood Logs Outdoors Under the Forest Canopy

By Paula Vopni and Bruno Pretto

Woodlot owners are familiar with the many colourful and delectable mushrooms that emerge from the forest floor after spring and autumn rains. These mushrooms are much sought after, and wild mushroom gathering and cooking are delightful and rewarding activities. While these “earth” mushrooms, such as chanterelles, morels, and truffles, are ephemeral and difficult to cultivate, there is a whole category of more reliable “wood” mushrooms that grow on trees and fallen logs in natural woodlands. These wood mushrooms can be purposefully cultivated in a controlled manner. This article is intended to give you a basic understanding of how you can cultivate nutritionally valuable, gourmet mushrooms such as shiitake and oyster mushrooms on hardwood logs outdoors under the forest canopy. You will find some valuable references at the end of the article for further learning and for ordering mushroom growing supplies.

Managing woodlots often involves thinning trees to improve overall health and productivity. Shiitake cultivation fits well with good forest management and is a sustainable use of forest resources. A woodlot owner can put hardwood logs into mushroom production for a relatively modest investment of time and money. Such a forest gardening or agroforestry enterprise can be quite small, with perhaps a dozen logs to supply mushrooms for your own table. Or, the enterprise can be much larger, with hundreds of logs to supply mushrooms for barter or sale. Growing mushrooms can be an intensive effort with active, aggressive management of the logs, or it can be casual, where environmental factors such as rainfall and temperature are allowed to drive production.

Many regions in the northern U.S. and Canada have ideal conditions and raw materials for outdoor mushroom cultivation. Ontario is certainly one of these regions. The cultivation of shiitake mushrooms, in particular, outdoors on hardwood logs, is tried and true. The success rate is high when attention is paid to key details.

Shiitake and oyster mushrooms are gourmet wood mushrooms that have proven health benefits. Adding wood mushrooms to your diet will enhance your health, and growing them yourself will yield high-quality mushrooms at a fraction of what you would pay at a grocer. Such an enterprise can be rewarding on a personal level and can also present an income opportunity as well as a way to connect and interact with your local community including neighbours, resorts, restaurants and markets.

Species of wood to use

Both white and red oak (Quercus spp.) are rated as excellent species for shiitake cultivation. The wood is dense and the bark tends to stay on the log. Oak will produce for a relatively long time, so you will get the most mushrooms for the initial investment.

Sugar maple (Acer saccharum) is also rated as excellent for shiitake cultivation. It is reliable and the taste can be superior. Other hard maples can also be used as a substrate for shiitake. The softer maples can be used for oyster mushroom production. Red maple is also good but is a softer maple and has a shorter life span.

Ironwood (Ostrya virginiana) comes next in terms of suitability for shiitake cultivation and is rated as very good. Some claim it is as productive as oak.

Musclewood, also known as American hornbeam (Carpinus caroliniana), is also rated as very good. It produces large specimens of shiitake, but the flavor may be inferior.

Beech (Fagus grandifolia) is also rated as very good and may even outperform oak.

Birch (Betula spp.), including white birch, sweet birch, black birch and yellow birch, are all rated as good for shiitake cultivation.

Bitternut hickory (Carya) is also rated as good — it seems to colonize more slowly but produces high-quality shiitake.

Species that are NOT suitable for shiitake cultivation include white ash, elm and soft hardwoods, such as aspen and poplar, which are more suitable for oyster production. Oysters will grow on all the species that are recommended for shiitake as well as on the softer woods. Do not use evergreen species such as pine, spruce, hemlock or cedar, as they contain anti-fungal resins. Fruitwood including apple, cherry and other fruits are not recommended. Further research is needed with chestnut, walnut, elm (low production), alder and other hardwood species. Western alder is suitable and is used on the west coast of the U.S. and Canada for shiitake cultivation.

Cutting wood for mushroom cultivation

The best size for logs, or bolts, is four to six inches in diameter. Larger logs can be used but are more difficult to handle (moist/wet logs are heavy). The four- to six-inch diameter range is ideal because it optimizes the amount of sapwood per volume of log. It is the sapwood that the mycelium will colonize. It seems that the sapwood to heartwood ratio is higher in a tree that has been growing vigorously under optimal conditions compared to a less vigorous tree. Length is not as important as diameter, but short length logs dry out more quickly. Generally, 4 inches is the length recommended because that size is manageable to move and retains moisture. Large diameter logs of eight to 12 inches can be shorter so that they are still manageable to handle.

Moisture content of the wood and the integrity of the bark are the key factors to consider when deciding when to cut your logs. The most important consideration is retaining moisture content. Fresh wood must be cut; do not use old deadfall wood as it will be dried out and already colonized by other fungi. However, limb wood that falls from a healthy tree during a winter storm is suitable to use the following spring. It is important that the bark be kept intact; care should be taken to protect bark during felling and handling. Damaged bark allows the wood to dry out and also allows invasion by competing fungi. Bark is negatively affected by prolonged direct sunlight and continual wet conditions; both should be avoided.

Winter and early spring, before bud swell (definitely before leaf bud), are the best times to cut logs, or limb wood. Bark is tight on the wood in the cold, dry weather and will not easily shred or slip off the log. Even though moisture content will be higher in early spring, you do not want to delay cutting until too late in the season as it can be difficult to get into the woods in early spring. Research at Cornell (see references at the end of the article) indicates that cutting thin-barked species like beech and red maple too late in the spring, when the buds are breaking dormancy, results in the bark separating from the wood and easily sliding off. This is a significant problem and can be avoided by cutting in winter. If cutting in early spring, it should be well before bud swell. Also, it is best to cut wood at least four to eight weeks prior to inoculation to allow tree tissues to die and secondary substances (anti-fungal substances) to break down. Felled logs can be left in the woods, off the ground (perhaps on a skid), covered with snow, which will block out the drying winter sun and wind; the melting snow keeps logs hydrated. Logs can be protected from sun and wind with pine boughs or shade cloth that allows rain and snow to penetrate.

When to inoculate

In southern Ontario, May is the ideal month for inoculation. Thus, the window of opportunity for cutting wood is from mid-November, at the earliest, until mid-April, at the latest. This allows ample time for the spawn to “run” through the sapwood and to establish itself during the summer and autumn before winter sets in. If inoculation is done too late in the season, the spawn run will be shortened by the onset of freezing temperatures which will negatively affect the colonization of the wood and the survival rate of the mycelium. Felled logs should be piled off the ground to avoid them getting muddy in the spring thaw, and out of direct sun and wind that will dry them out. The ideal log moisture content at inoculation is from 35 percent to 55 percent. If logs dry out before inoculation, they can be soaked or intensively sprinkled to raise the moisture content. However, little water moves through bark; mostly it enters logs through the exposed ends. Since logs do not absorb water readily, it is important to prevent moisture loss between felling and inoculation. Protect logs from direct sunlight; keep them in a shaded area or cover with pine boughs or breathable shade cloth that allows rainfall and snow melt to penetrate. Stacking patterns that work best for incubation and harvesting are discussed below. Stacking for incubation should protect logs from sun and wind and also allow ventilation around each log. Stacking or standing logs up for harvesting should provide protection but also allow for easy access to each log [see figure 4 below for good and bad stacking patterns].

Inoculation

Figure 2 wFigure 2: Diamond pattern for inoculation; note extra holes around branch stub and near endsInoculation is the introduction of spawn into the wood; spawn is sawdust that has been colonized by the mycelium of the mushroom fungus. Inoculation is done by drilling holes and filling them with spawn. It is done in the spring when daytime temperatures are 10º C. There is no standard number of holes per log, and different inoculation patterns are used; row/ring and diamond patterns are common. A general rule of thumb for estimating the number of holes per log is no less than one row of holes for every inch of log diameter, with holes spaced every six inches along the row. This pattern gives rows and rings evenly spaced around the log, but a modified diamond pattern is easier to drill and fill and is equally effective [figure 2]. Extra holes near log ends, branch stubs and wounds will quickly establish mycelium near the most likely sites of invasion by competing fungi. High inoculation rates speed colonization and may produce mushrooms sooner but will increase spawn costs.

Depth of holes

Holes are drilled to a depth of approximately one and one-eighth inches. The objective is to drill into the sapwood and leave a tiny air space under the spawn. This allows the spawn to jump off onto the sapwood more easily.

Tools required

You need a drill and a wood bit. The actual size of the bit depends on the spawn format. You want the dowel or the sawdust plug to fit snugly into the hole. When using a manual hand inoculator, the size of the bit should match the size of the tool, but since the spawn is loose, there is some wiggle room. When using dowels or sawdust spawn plugs, you want the bit size to match fairly closely to the size of the dowel or plug.

Sealing the holes

Following inoculation, the holes must be sealed to keep moisture in and competing fungi out. Traditionally, loose spawn has been used to inoculate logs. A hand inoculator or plunger type instrument is used to introduce the spawn into the holes. Each hole must be sealed with wax — cheese wax or beeswax rather than paraffin. Dowel plugs that have been colonized with mycelium are also used and, again, the holes must be sealed once the dowel is inserted into the hole. Sawdust spawn plugs that are backed with Styrofoam caps are a more recent development and they have several advantages. The plugs are easy to insert, the spawn jumps into the wood easily, the spawn run is faster than for dowels, and the holes do not need to be sealed with wax, which saves a lot of time.

Spawn Run / Incubation

Figure 3 wFigure 3: Mycelium at ends of logs following incubation.Once in the log, the fungal mycelium will run through the vascular vessels of the sapwood (layer of wood outside the heartwood) and colonize it. After spawn run, the white mycelium will show at the ends of the logs in a ring pattern that follows the contour of the sapwood.

Generally, this will take about four to six months. You want the mycelium to be well established before winter when the mushroom mycelium will become dormant. Logs remain outside during the winter. The following spring, the logs will begin to “flush” with mushrooms after the first rains.

Harvesting

Logs will begin to produce mushrooms one year following inoculation. If the spawn is introduced early (May) and environmental conditions are favourable during the spawn run/incubation period, some mushrooms may emerge in the autumn, but in Ontario, full production will not begin until the next spring. The second and third years after inoculation are generally the most productive. The rule of thumb is that logs will last one year for every inch of diameter — so a six-inch log will produce for six years. Harder woods will last longer and be more productive. Another rule of thumb is that you will get about one pound of mushrooms per log per year, but yield will depend on the hardness of the wood, the environmental conditions, and your handling and management techniques.

Once mushrooms begin to emerge, it is a matter of days before they can be harvested. Logs must be monitored so that emerging mushrooms can be harvested at the optimal time. Flushing logs, as shown in figure 1, can be protected from rain as this will soak the developing mushrooms and affect quality. Mushrooms can be dried in the sun, but you want to avoid the need to actively dry mushrooms due to the energy cost involved.

Stacking patterns for incubation and harvesting

Laying yard

Figure 4 wFigure 4: Stacking PatternsDuring incubation, logs should be stacked in crib arrangements, close to the ground, but with ample ventilation around logs as shown below. Dead piles are poor because there is no air movement around the logs, and A-frame stacking is a poor use of space. Logs do not need much light for incubation, but ventilation around the logs will preserve the bark. Shade cloth or pine boughs can provide protection from the sun if needed when the leaf canopy is bare in early spring and winter.

Fruiting yard

Following incubation and during harvesting season — May to November — logs can be arranged so that picking is easier. You want easy access around each log. A lean-to arrangement as shown above works well; modified versions with logs contained between two side rails and end supports is quite efficient and allows for easy picking [figure 6]. Logs can be leaned against barbed wire strung between poles (as shown in figure 5) or simply leaned around standing trees in a tepee arrangement.

Log Management

Figure 5 wFigure 5: logs leaning on barbed wire between posts for harvesting Key factors that influence mushroom production are moisture and temperature. Situating logs near a water source is important if you want to actively manage your logs. Frequent short-term watering/sprinkling is not suitable for mushroom cultivation. During harvesting season, a regime of intermittent soaking — either by natural rainfall, or by overnight sprinkling (48 hours), or by immersion under water (overnight – 18 hours) — interspersed with periods of drying out in a well-ventilated area is best. Intensive management to control the fruiting of logs involves forcing them by soaking. This can be done every eight to 12 weeks. Forcing gives you more control but will shorten the life-span of the logs. Situating logs in stagnant air, as in a basement or a low-lying swamp, is not ideal as it may encourage de-barking. Once bark comes off, the wood will dry out and the mycelium will die. On the other hand, too much wind will dry logs out, so keep them in a protected area, closer to the ground (under four feet high). Logs need a day/night regime — complete darkness will inhibit fruiting, and logs kept under a deck or in a basement will not produce for long. Direct sunlight hitting the logs for hours at a time, especially during the late afternoon, will overheat the logs, negatively affecting the bark, and inhibiting mushroom fruiting. Dappled sunlight filtered through the forest canopy is ideal. The resources listed at the end of this article will provide more detail about log inoculation and management techniques.Figure 6 wFigure 6: modified lean-to for harvesting

Marketing

If you decide to engage in a small commercial operation you will have to find sales outlets for your mushrooms. This will depend on the particular situation in your locality. Some research will be necessary to devise a marketing plan. You will have to figure out who your target market is and what price you can ask. You may want to simply barter with neighbours or you may decide to “go retail” and attend a farmers market. Your desire to work, driving distance to customers, and availability of storage facilities will all enter into the equation. Local food is a growing trend, and you may find a restaurant or resort that may want to take all of your production. This gives you an opportunity to get to know local chefs, store managers, food processors and neighbours. Connecting with the local community and having fun while making a bit of money is the aim. This is not a get-rich-quick kind of thing. It’s a high-touch, low-tech kind of thing. But I can tell you from personal experience that it is a sublime experience to walk into the woods and discern these almost mystical shapes, appearing to float in the dappled sunlight among the trees, quietly waiting for you. Nature provides. And money, it seems, does indeed grow on trees.Figure 7 wFigure 7: high-quality Shiitake ready to be harvested

References for further learning:

www.mycosource.com The author’s website. Mycosource Inc. is located in southern Ontario. Mycosource Inc. produces shiitake and oyster mushroom spawn.

“Best Management Practices for Log-Based Shiitake Cultivation in the Northeastern United States” Cornell University, University of Vermont Extension, and Sustainable Agriculture Research Education (SARE). 2013

The Shiitake Growers Handbook: The Art and Science of Mushroom Cultivation by Paul Przybylowicz and John Donoghue, Kendall/Hunt Publishing

Growing Gourmet and Medicinal Mushrooms by Paul Stamets. This is a comprehensive guide to the cultivation of many species of gourmet and medicinal mushrooms. Paul Stamets operates Fungi Perfecti in Washington State and has talks on TED and on TED/MED.

Note: Drawings are from The Shiitake Growers Handbook and from Growing Shiitake in a Continental Climate by Kozak and Krawczyk (out of print). Photos from Mycosource Inc.


Disclaimer

Information on this website may be accessed and downloaded, but please do not reproduce or duplicate without the consent of the OWA.

Member Login

eLetter