Mushrooms in Agroforestry - Spring 2002
As one of the premier nutrient recycling organisms in the world, fungi are naturally an important component of any farm or garden. Along with organisms such as bacteria and yeasts, fungi are responsible for the activity in compost—just watching a compost pile cook down to fine, crumbly soil is proof of their power. Fungi can aid in the decomposition of straw, corn cobs, woodchips, or sawdust, as well as hard-to-handle forestry waste products like tree stumps and logs from small diameter trees. Their ability to break down such materials is important because this makes nutrients available for a farm or garden's plants and animals.
Many mushrooms are well adapted to growing under forest cover, so growing them can be a good fit for anyone considering ways to incorporate a stand of trees on their property into their overall farm or garden plan. Fungi are cold tolerant and are easy to grow organically throughout the Northeast. Also, since they don't have to be replanted each year, most of the work is done in the first season. Mushrooms need little daily care, add a superb accent to a fresh dinner from the garden, and can be an eye-catching addition to a grower's stand at the market.
A mushroom, the part of the fungus we see, is just the fruiting body of a large, intricate network of filaments, called mycelia. Fungal mycelia live in the soil and in organic matter, especially wood, in every ecosystem of the world. These fine filaments intertwine and connect in an intricate network that carries nutrients, water, and minerals to nourish the fungi.
When neighboring mycelia of the same species come into contact, and the pH, temperature, and humidity are right, the mycelia may join and form a mushroom. A single mushroom is capable of producing invisible clouds of spores which colonize new substrates and grow into new mycelial networks. Picking a mushroom has been likened to plucking fruit from a tree—it's unlikely that the mushroom we see is the only fruit the mycelium will produce, at least until it exhausts its food source.
There are two kinds of mushrooms that a cultivator can grow—the decomposers and the symbionts. The first kind, the decomposing fungi, are also called saprophytes, and they are the main type of mushroom considered for gourmet cultivation. Their mycelial nets interweave throughout and between the cells in dead plant matter, secreting powerful enzymes and acids that act to reduce complex molecules into their basic components that are readily available for uptake by the fungus itself as well as other plants and organisms.
Saprophytic mushrooms colonize dead plant matter, or substrate, and work vigorously to extract all of the readily available nutrients. These mushrooms include the oyster, lion's mane, hen-of-the-woods, and shiitake mushrooms. Our most familiar mushrooms are also in this group: portobello, crimini, and button mushrooms, all of the same genus, Agaricus.
The second kind of fungi is symbiotic with plants, and like the nitrogen producing bacteria present in the roots of garden peas and clover, they cooperate with trees, shrubs, or other plants. They are a common and important component of forest ecosystems. Their mycelial nets, being much finer than plant roots, are able to gather large amounts of water and trace minerals from the soil, which are shared with plant rootlets. For its part, the plant shares the some sugar it produces photosynthetically with the mycelium, and so both organisms benefit. Trees have been shown to grow much more vigorously in the presence of these symbiotic, or mycorrhizal fungi. Some nurseries have even specialized in inoculating tree seedlings with mycorrhizal mushrooms to be used to regenerate clearcut forests, since the trees grow so much better.
What Kind to Grow?
Choosing which varieties to cultivate may well be the toughest aspect of growing mushrooms. Most folks are familiar with the rich and robust shiitake, but the other wood-loving varieties also have a lot to offer. Chicken-of-the-woods mushrooms are very meaty and absorb cooking flavors well, and the hen-of-the-woods, or maitake as it is known in Japan, has a pleasing mild flavor. Wood ear mushrooms are excellent in soups, lion's manes grow like a white pom-pom and resemble lobster in taste and texture, and oyster mushrooms are heavy yielding, sweet tasting mushrooms that are excellent in a stir fry. Other mushrooms that can readily be grown include morels, which make the best cream of mushroom soup, and the amazingly vigorous King stropharia. All of these mushrooms are indigenous to the Northeastern US, except the shiitake and wood ear. Visit www.fungiperfecti.com to see photographs and descriptions of these commonly grown mushrooms.
All edible mushrooms contain substantial amounts of protein and trace minerals, and many also have medicinal properties. These medicinal effects are probably the result of complex molecules present in the mushroom and mycelia called polysaccharides that the fungi produce to inhibit the growth of molds and bacteria in a mushroom. Practitioners of eastern medicine have been using mushrooms for a long time and researchers in China and Japan have conducted many studies that prove their healing properties. Such studies are beginning in the U.S. now, too, which should lead to more widespread acceptance of mushrooms as agents of healing. Anti-viral, anti-bacterial, anti-tumor, and immune system enhancing properties are exhibited by the maitake, reishi, shiitake, and nearly all of the shelf mushrooms. New drugs to fight cancer, herpes, and influenza A are being developed from these and other mushrooms, and some of their unique anti-viral compounds have even shown the ability to inhibit the replication of the virus that causes AIDS.
Shiitake mushrooms also effectively lower cholesterol levels in the body—a single cap sautéed in a whole pat of butter will still help to lower a person's blood serum cholesterol. One can gain all of the medicinal benefits of mushrooms by simply consuming them, either in a scrumptious dish in the case of shiitake, oyster, lion's mane, or maitake, or powdered in tea in the case of the woody reishi or shelf mushrooms.
Mushrooms and Organic Standards
There are currently no rules for mushroom production under the new standards issued by the USDA. According to the National Organic Program (NOP), until those rules are in place, certified growers may produce and label mushrooms as organic as long as at least a portion of that production is certified by a USDA-accredited agent. Also, the mushrooms can't carry the USDA seal, but must display the certifying agent's seal or other identifying mark. See http://www.ams.usda.gov/nop/noppolicies.htm for more information. That said, growing mushrooms organically outdoors is easy. They require little but occasional watering after their initial inoculation into a substrate. Any farm that is already organically certified for vegetable crops ought to have no problem selling outdoor-grown mushrooms as organic.
Ways to grow mushrooms outdoors
One can grow many kinds of mushrooms on the types of hardwood tree species common in the northeast. Shiitake, chicken-of-the-woods, maitake, wood ear, lion's mane, oyster, and reishi mushrooms are a few good candidates. On average, each log will cost $1-$3 to inoculate, depending on the type of spawn ordered and how much is introduced into each log—the cost is around $20 to inoculate 20 logs.
Mushroom spawn is actively growing fungal mycelium and is available either as plugs (1" wood dowels) or in sawdust. Successful introduction, or inoculation, of this spawn onto a new substrate will produce mushrooms for years. When selecting a variety for cultivation, one should consider flavor, vigor, edibility vs. medicinal properties, marketability, and time until harvest. Companies that sell spawn offer a great deal of information on these topics (see resource list).
Proper log selection is crucial to the success of the project. Hardwood logs can produce mushrooms for up to six years. Softer woods like aspen or poplar will yield mushrooms sooner, but will not produce as long as the denser woods. Conifer and fruit tree woods are notoriously bad for growing mushrooms and should be avoided. Tree species with thicker bark retain more moisture and protect mushrooms from drying out (a dry mushroom is a dead mushroom). For this reason, birch is not highly recommended for log culture, while oak is considered the best, and maple, hickory, ash, beech, poplar, ironwood, cottonwood, aspen, willow, and elm will all support vigorous mushroom growth. The logs also need to be small in diameter, from 3 to 10 inches, and two to four feet in length. For this reason, growing mushrooms on the small hardwood trees thinned from a woodlot makes good sense.
Logs should to be alive when cut. Unless spawn is introduced to a log before it is two months old, it is likely that another mushroom strain will colonize it first. The best time of year to harvest logs is winter or early spring when all of the tree's sap is still in the trunk of the tree. This sap is crucial to the proper nutrition of the fungi. A log from a tree that is fully leafed out will support mushrooms, but not as well as a log cut from a dormant tree. (This type of project can really put a person's tree ID skill to the test. If you find it difficult to identify dormant trees, borrow a knowledgeable friend, or get a field guide and mark the suitable specimens while they still have leaves). Once the logs are sawn to the proper length, be careful to leave the bark intact, as exposed wood leads to contamination and dessication, and be sure to keep logs clear of the ground until inoculation.
Tools needed for log culturing include a hammer or mallet, natural fiber paintbrush, cheese wax, and a drill. To introduce spawn to a log, drill holes one inch deep (a drill stop is useful, as holes that are too deep inhibit rapid colonization by the mushroom, and shallow holes will leave dowels exposed) and fill them with plug or sawdust spawn. Spawn suppliers will furnish advice on the width of the holes and how many holes should be drilled per log—more dowels should be inserted to produce more rapid blooms. A good rule of thumb is 30 to 50 plugs per log, tapped into evenly spaced holes 4 to 6 inches apart in a diamond pattern. Melted cheese wax (also available from spawn suppliers) applied to the ends of the logs and the heads of the dowels will keep out contaminating spores of other mushrooms and keep moisture in.
Another method is to cut logs into two or three one-foot sections, placing a layer of sawdust spawn between the ends, and then nailing the pieces back together. Alternatively, some growers cut a V shaped wedge out of the log, fill the cut with sawdust spawn, and then nail the wedge back on. Those who want to avoid cutting or drilling can simply pack sawdust spawn onto the log ends and make an aluminum foil "swimming cap" to hold the spawn in, but since the foil is liable to tear, contamination by unwanted fungi becomes more likely.
Locate a spot for the newly inoculated logs near a water source and under existing tree cover to ensure success. Logs need watering or soaking in a pond or tank during dry times, and will produce best if soaked once a week until their first fruiting. It is best to allow the bark to dry between soakings to deter the growth of unwanted fungi species. Logs should be lain in the shade in flat stacks called ricks, or if they are far from a water source, they can be buried 1/3 of their length in the soil, standing upright, so that moisture will be drawn into the wood naturally.
A final important task is to mark each log with a durable label, such as the aluminum tags offered by some supply companies. Recording the date of inoculation and the type and strain of mushroom on these tags will help the cultivator determine how well various types of mushrooms perform in the region.
Although all wood loving mushrooms can be grown on sawdust or other substrates indoors all year long, this is a much more technical operation and requires substantial investment. Mushrooms grown on logs outdoors are firmer and more robust, bring better prices, and seem to be more flavorful. While yields from outdoor mushroom operations are seasonal and not great enough to be profitable, they do supply a fine supplemental income for many cultivators. The website www.mushroompeople.com has a table that can help determine the income potential of a mushroom growing operation.
Mushrooms can also be effectively grown on the stumps of freshly felled trees. The length of time until first harvest is longer than that for log culture, given the sheer size of the substrate, as fungi will usually fruit only after the whole available substrate has been completely colonized. The clear advantage of this method is that the mycelium benefits from the stump's natural function of transporting water from below ground to the surface. When the mushrooms appear, they can be in huge clusters.
It is important that stumps be fairly fresh, so that the grower can be mostly certain that what is growing is what was intended. Even so, it is helpful to know what other kinds of mushrooms may grow on wood in the neighborhood. Stumps are best located under tree cover, to prevent drying out.
When inoculating stumps, space the holes for dowels or sawdust spawn 4 to 6 inches apart in rows or rings in the sapwood. Sealing the holes with wax is recommended to keep out other mushroom species. Oyster, maitake, and reishi are particularly good for growing on stumps, and may produce mushrooms for a dozen years or more.
Oyster mushrooms and the King stropharia mushroom can be grown on fresh sawdust and wood chip piles, on fresh chopped straw dug into soil under trees, or on wood chips in between garden beds. Paul Stamets, in his excellent reference Growing Gourmet and Medicinal Mushrooms, notes that crops growing near fungi do very well, benefiting perhaps from the mushrooms' ability to make micronutrients available in the soil. Stamets' company, Fungi Perfecti, sells kits to grow Shaggy Mane, King stropharia, and oyster mushroom patches in garden aisles between crops and under trees. Even bees love mushroom patches—Stamets' book notes an instance where a King stropharia patch was ferociously fed upon by that farm's hive. The bees burrowed into the sawdust and devoured the sugar-rich mycelium for weeks.
Other varieties of mushrooms that can be grown in patches include some of the more valuable ones, like morels—many companies now offer their spawn. The even more delicious chanterelle should become available in coming years. Patches often require special amendments or treatments, such as areas of burned ground in the case of morels, in order to flourish. The supplier of the spawn can advise best how to achieve success. It's also best to have a source of water nearby to ensure the harvest.
One emerging industry is the growing of truffles, the most sought-after of all mushrooms. The black perigord truffle, as the European variety is known, goes for as much as $250-$400/lb wholesale and $750-$900 retail—not bad for a crop that requires little effort. Other attractive aspects of growing these "black diamonds" is that they can produce for as many years as the tree is alive, and harvest is mid November to mid March, precisely the time that other sources of on-farm revenue may lag.
Since truffles are symbionts with trees, one must purchase trees whose roots have been inoculated with truffle mycelium. Since truffles don’t grow well in acidic environments, the typically sour northeast soils would have to be amended with lime prior to planting any trees. Potentially, rows of truffle trees could be planted and crops grown in between, so that the crops gain the advantage of shade during hot summer months and are protected from the damaging/drying effects of the wind. Another possible use could be planting the trees out in pasture and allowing grazers to enjoy their shade as well, so long as they don't nibble the trees too much.
The catch is that it takes years before the first harvest—digging is not encouraged for several years to allow proper establishment of the colony—and so truffle growing must be viewed as a longer-term investment. At $17-$20 per tree, the cost can be prohibitive if one is to grow as many as 500 trees per acre, as some commercial farms do. One also needs to train a dog to find them, as the traditional pig will devour too many freshly found truffles.
In just five years, though, each tree can produce up to 2 pounds of truffles each. Yields vary, and this is an unproven industry in North America as yet. Growers in Oregon are having success growing the black truffle and the indigenous white truffle, too. Contact mushroom supply houses to find companies that can supply trees and information, but be sure that they are selling the real thing. Some unscrupulous dealers are selling trees inoculated with "false truffles." They look like the real thing but are of little value.
For those who are interested in mushroom culture but want to start out slowly, many spawn sources offer easy-to-grow organic mushroom kits, which are usually compacted sawdust blocks pre-inoculated with the mushroom of your choice. Just add water and watch them grow! These also make great science projects for kids. Nearly all mushroom supply companies offer kits for around $20.
When harvesting mushrooms, the grower ought to use a knife and cleanly slice through the stalk at its base, leaving as little mushroom attached to the substrate or log as possible. This will prevent contamination problems posed by molds that may land on ragged mushroom stumps. Shiitakes require a very sharp knife, as they have stout stalks which are tough to cut through. Reishi mushrooms, though, are brittle and one can snap them off fairly cleanly with ease.
Mushrooms can be an integral part of any farm or garden, both for their valuable ecological functions and their nutritional and medicinal properties. Experiment with methods that produce desired varieties and consult some of the excellent references on growing mushrooms outdoors to boost yields. Growing mushrooms outdoors is truly an art that anyone can master and enjoy, so why not give it a try this year?
Mushroom Cultivation Books
Mushroom Identification Guides
Mushroom Supply Houses
There are many companies offering spawn and a simple online search can locate a number of them. Two of the best are:
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