You may have heard the term “Mycorrhizal Fungi,” sometimes called “Mycos” in recent years, but what, exactly are they? The origins of the word offer the simplest explanation. “Myco” comes from the Latin word for fungus and “rhiza” is Greek for root. These “fungus roots” can be greatly beneficial to gardeners.

Mycorrhizal fungi belong to the same group as mushrooms, the fungus kingdom. A mushroom is similar to an apple, it is the fruiting body of a larger organism. But rather than growing from a tree, the mushroom is formed from an interconnected network of root-like tubes called hyphae. Most hyphae are very small, between a tenth to a fiftieth of the width of a human hair, making many of them invisible to the human eye.

More than 450 million years ago, certain types of plants and fungi formed a symbiotic, or mutually beneficial, relationship with each other. The plants give the fungi sugars that they produce through photosynthesis, in exchange, the fungi give the plants nutrients and water that they extract from the soil. 80-95% of land plants benefit from some type of mycorrhizal relationship.

What does this mean for gardeners? Lets say you plant a seed in soil without any mycorrhizal fungi. The plant’s roots will go out in search of nutrients and water to feed its growth. As the available resources are used up in one area, the roots grow further and further, expending more and more of the plant’s energy. Now, let’s introduce some mycorrhizal spores. The plant send signals out to any mycorrhizal fungi in the area and the spores respond by growing hyphae in the direction of the signal. If a spore is able to find the root of the plant, the hyphae will penetrate the root and begin to grow structures that allow for the plant and the fungi to exchange resources. The mycorrhizal fungi will now begin growing an extensive, cottonball-like mass that will give the plant access not only to the nutrients and water outside the reach of its roots, but, since the hyphae are so small, they can access nutrients in the small spaces between the roots as well.

Though most commonly grown plants will benefit from mycorrhizal applications, there are a few exceptions. The brassica family, which includes such plants as broccoli, cabbage, radishes and kale is one. Beets, chard, blueberries, cranberries and rhododendron are some others.

Though mycorrhizal fungi are naturally occurring in most soils, the application of fungicides and pesticides, the use of heavy machinery, and leaving soils without any plant growth for weeks at a time, have created soils with little or no mycorrhizal fungi populations. The ground surrounding newly built residential neighborhoods and commercial properties is particularly lacking. Only in recent years have commercial mixes become available to reintroduce these important organisms back into garden soils.