Gardening Articles: Landscaping :: Yard & Garden Planning

Helping Plants to Help Themselves

by William Bryant Logan

Fertilizer doesn't feed plants. The sun feeds plants. And seventeen chemical elements--14 derived from the soil and 3 from air and water--help plants use the sun's light to build carbohydrates to use as food. Yet people still feed their plants with high-nitrogen fertilizer to make them fat and glossy. The results are often increased insect and disease attack, water pollution, reduced drought tolerance, and in the case of mature trees, even decline and death.

What if you could reduce fertilizer use and instead offer your garden's plants a way to help themselves? That is what mycorrhizal inoculation does. In the past two years, products containing mycorrhizal fungi have begun to appear in garden centers, home improvement stores, and mail order catalogs.

Don't let the big words worry you. They mean simply to place spores of special fungi in the root zones of new and established trees, shrubs, annuals, and perennials. Dr. A. B. Frank, a German scientist, coined the term "mycorrhizae" in the late 19th Century from the Latin word myco (fungus) and Greek word rhizae (root). The fungi colonize plant roots and, in effect, quickly create masses of new "fungus roots" that dramatically increase the plant's ability to absorb water and nutrients and fight off disease. Fine strands called hyphae penetrate soil particles that plant roots can't reach. At the same time, the fungus feeds on sugars from the plant.

Surprisingly, the vast majority of land plants naturally form symbiotic relationships with mycorrhizal fungi. Pull up a wild seedling most anywhere, and looking closely enough you will likely find mycorrhizae. The only places not rich in mycorrhizae are those disturbed by human activity. In fact, mycorrhizal inoculation was first developed during the 1970s to help reforest spoiled lands such as strip mining sites. As it turns out, mycorrhizal inoculation is equally valuable for many urban and suburban soils, where drought and compaction are problems.

Recent studies show that the addition of mycorrhizal fungi measurably helps young and established trees, shrubs, annuals, and perennials growing in soils typical of roadsides and garden edges. My experience with Urban Arborists in New York City, suggests that--particularly with mature oaks in park and roadside settings where slightly acid pH is maintained but where soil compaction is extreme--placing mycorrhizal inoculants in auger holes can prolong the life and improve the looks of the trees. Less dieback seems to occur on branches, and the trees leaf out vigorously and appear better able to withstand drought.

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