Mycorrhizae Help Feed Your Plants

One of the most valuable organisms your soil can have is a fungus known as mycorrhizae, which means “fungus root” in Greek. The full name of the fungus will really make an impression at your next cocktail party: vesicular-arbuscular mycorrhiza (VAM), a fancy name for a fungus that every gardener should know intimately.

Mycorrhizae are fungi that establish a graceful, symbiotic relationship with the roots of most plants. They invade the roots of vegetables, flowers, shrubs, and trees; connect them, one to the other; and then send out their filaments, called hyphae, as much as 200 times farther into the soil than the roots they colonize. Mycorrhiza has the ability to better mine this wider area for water and nutrients, especially phosphorus, which it transmits back to the roots. The plant pays for this service with the glucose the fungus needs.

This extended feeding area makes mycorrhizae-associated plants just plain healthier. They have better root formation as well as fewer root diseases and other soil pest problems. They also require less moisture and fertilizer, while showing an increased tolerance to salt.

Gardener’s Glossary

Apical dominance. The highest bud on a shoot or branch, known as the apical bud, will release a hormone that inhibits the growth of any buds lower on the shoot or branch. The apical bud will then grow faster, straighter, and taller than the other buds.
Coppicing. In late winter or early spring, many shrubs and trees can be coppiced, or cut back to within a few inches of the ground in order to spur vigorous new growth or to control size.
Pollarding. Serving the same function as coppicing, pollarding is the cutting back of a tree with a single main stem. In late winter or early spring, the branches are pruned back to within a foot or two of the main trunk.
True leaves. When starting seeds, it’s the appearance of the seedling’s first set of true leaves that signal it can be moved to a larger container.The first leaves to emerge after germination are cotyledons, a source of nourishment for the new seedling. The true leaves are those that emerge after the cotyledons.

The key to this wonderful, subterranean environment is the undisturbed labyrinth of hyphae. Tilling and even simple hoeing can rip apart this delicate lace, which can then take months or even years to reestablish. When tilling is a yearly event, the fungus will never get a foothold. Too much synthetic fertilizer can also damage the fungus, as can pesticides and, of course, fungicides. Solarizing your soil (covering it with clear plastic to let the sun’s heat kill weeds and insects) will also destroy mycorrhizae.

Soils high in organic matter are where mycorrhizae flourish, so adding compost is one of the best ways to encourage the establishment and growth of the fungi. Rather than digging in organic matter, which will destroy the fungal net, lay the compost on top of the soil and let it naturally decay into the soil.

Mycorrhizal inoculants are available from several companies, but adding these to your soil is usually not necessary unless the soil microbe population has been damaged. In addition, many strains of VAM are plant specific, and what you buy may not be the right one. Often, the products will contain a mix of many different fungi in the hope that one will match your plant.

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