The Dirt on Mycorrhizae

By on September 04, 2015

Photo of Ectomycorrhizae on Picea glauca roots. By André-Ph. D. Picard

Myco-what? Pronounced my-coh-RYE-zay, scientists and gardeners both have been learning more in recent years about this fungus and how it benefits the garden and ecosystem. But just what is it, and why do your plants need it?

Tiny plant helpers

Mycorrhizae, meaning “fungus-root,” are a kind of fungus that live symbiotically with plant roots. Approximately 95% of the world’s plant species are able to form symbiotic relationships with mycorrhizae. A notable exception is vegetables in the Brassica family, such as cabbage, broccoli and radish, which do not form any mycorrhizal relationships. While few plants require mycorrhizae to survive, those that can grow with the help of this fungus are bigger, stronger and healthier than they would be without mycorrhizae.

Mycorrhizae help plants in many different ways. Their primary benefit is in plant nutrition. Mycorrhizae help both by increasing nutrient availability in the soil and by directly depositing nutrients in or near plant root cells. In legumes, nitrogen-fixing bacteria work in concert with mycorrhizae to function at peak efficiency. Mycorrhizae also improve soil structure, locate good soil for the roots to spread, take up nutrients from the soil and carry them to the roots, and inhibit other soil microbes.

Endo or Ecto?

There are two kinds of mycorrhizae: endomycorrhizae and ectomycorrhizae. Both live partially within the roots of their host plants, and also spread away from the plant roots into the soil.

Endo (meaning “in”) mycorrhizae penetrate into the cells of the roots of plants with which it forms relationships. These mycorrhizae deliver nutrients directly into the plant cells. A wide range of plants can live symbiotically with endomycorrhizae including most vegetables, grasses, flowers, shrubs and fruit trees. 

Ecto (“out”) mycorrhizae live in between the cells of roots forming a “net” through the root, and also coat the outside of the root. These mycorrhizae deliver nutrients to the outside of plant cells with which they are in direct contact, but the plant must absorb the nutrients into the cells itself. Ectomycorrhizae form relationships with only a few kinds of trees including oaks and conifers.

Improving your soil with fungi!

There are many species of mycorrhizae, which typically can form relationships with multiple species of trees, flowers and garden veggies. Scientists have even discovered that one mycorrhizal fungus can simultaneously inhabit the roots of two or more different species of plants, and this connection is so strong that the health of one plant directly affects the other.

Mycorrhizae is present in most soils, and it can be encouraged to grow and flourish by caring for your soil with mulching, cover cropping, adding organic matter, and by not making rapid changes to the soil nutrient levels or pH. Low or no-till farming and gardening is better for mycorrhizae than conventional tillage. 

To add more mycorrhizae to your soil, you can inoculate your garden with Chappy’s Root Booster or Granular Root Growth Enhancer, or select potting soils or fertilizers with this ingredient. Some mycorrhizae also produce edible “fruiting bodies”: growing your own morel mushrooms is a delicious way to help your garden at the same time!

Check out the book Mycelium Running by Paul Stamets for in depth and practical information on these and other fungi.

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