Eugene Weekly : Gardening : 11.08.07

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Putting fungi to work in the garden

Somewhere between 460 and 400 million years ago, plants made the leap to dry land. And it’s possible they wouldn’t have survived it without fungi.


Like modern plants, and like their aquatic relatives, the oldest-known land plants captured energy from sunlight to make simple sugars out of carbon dioxide and water. Their ancient fossils also indicate an association virtually identical with those that form between fungi and the roots of modern plants. The association is a mutually beneficial one, providing a two-way flow of nutrients: sugars made by the plant pass through the roots to the fungus, while water and inorganic nutrients collected by the fungus are transferred to the plant. The structure responsible for this exchange — the colonized root — is called a mycorrhiza (literally, fungus-root). Since mycorrhizae have been around as long as terrestrial plants, scientist theorize that their presence helped aquatic plants make the challenging transition to dry land.

The science of mycorrhizae has grown by leaps and bounds since I first learned about them, as I discovered at a recent talk by Jeff Anderson of Mycorrhizal Applications, Inc. (MAI), a company that distributes mycorrhizal inoculant in a variety of commercial products. For one thing, the mycorrhizal condition is now considered to be the rule, not the exception. Under natural conditions, an estimated 95 percent of all plants form mycorrhizal associations with one or more fungal species. (Only weeds, apparently, get by without them.)

Since fungi form networks far more extensive than most plant roots and can exploit smaller spaces in the soil, mycorrhizae increase the absorbative power of root systems by 10 to 1,000 times. They also improve the structure of soil and can release hard-to-access nutrients from the remains of living things. Research shows that mycorrhizal plants grow better, show greater disease resistance and are better able to tolerate environmental stresses such as drought.

Although most plants can form mycorrhizae, the necessary fungi are not always present. They are lost when soil is disturbed by tilling or building operations or subjected to excessive use of chemicals. Growers can now choose to boost the soil’s mycorrhizal content with commercially available products, resulting in a reduced need of inputs such as fertilizer. Farmers can save money and produce healthier crops while reducing the level of damaging nitrates that leach into waterways. When I asked Anderson whether home gardeners could expect to benefit from adding mycorrhizae to their soil, he surmised that almost all would benefit. Only gardeners who have practiced organic gardening on their soil for years, combined with no-till or low-till methods, would likely observe little difference.

Most of MAI’s business is in agriculture and forestry, Anderson says, but another important application is ecological restoration on damaged or naturally nutrient-poor soils such as sand. Whether you are gardening, farming or restoring ecosystems, a variety of products containing a mix of mycorrhizal species is available for projects on any scale. For best results, the goal is to place your “mycorrhizal propagules” close to the root system of the target plant. You can incorporate granules in the soil, put a tablet in each planting hole, water with soluble product or plant bare-root starts that have been dipped in gel. Some soil mixes and organic fertilizer blends contain mycorrhizae.

All or some of these products are available from Lane Forest Products and Gray’s Garden Centers (look for the brand names Plant Success and EB Stone). Down to Earth sells a similar range of mycorrhizal additives under their own brand, and adds them to their own-brand potting soil and several fertilizer blends. One simple way to introduce the fungi is to use plant starts that have been raised in soil mixes that contain them. Many nurseries now use soil mixes (from Lane Forest Products, for example) that incorporate mycorrhizal fungi.

I switched to Down to Earth potting soil a few years ago. Within a week, I noticed such prodigious root development that I’ve stuck with the brand ever since. Recently, as veteran vegetable gardener and Down to Earth employee Karl Haga showed me some other mycorrhizal products at Down to Earth, I asked if he ever got feedback from customers. “Oh yeah! People think they’re great,” he said. “Do you want a personal endorsement?” He went on to describe an experiment with four pepper plants, two with, two without a single application of granules. The “with” plants were “one third greener, one third bigger and one third more productive.” Haga recommends putting granules in the soil at planting time and then watering in Soluble Root Growth Enhancer two weeks before flowering.

For more information about mycorrhizae, visit www.mycorrhizae.comand      

Rachel Foster of Eugene is a garden consultant and author of All About Gardens, a selection of past Eugene Weekly columns. She can be reached at