Do I Need Some Fungi?

Amanita-type mycelia
Amanita-type mycelia

I was thumbing through a gardening supplies catalog, looking at the assortment of “things you can spend your money on that your plants will probably do fine without” when my eye was caught by an offer for “mycorrhizae.” The catalog was extolling the many virtues of this fungal spore mix—it would improve plant health, make the plants more drought resistant, increase yields, protect against diseases, reduce the need for fertilizer, and cure my great-aunt’s bunions, all for $16.95 per pound.

It sounded too good to be true, so naturally I was highly skeptical. (It also sounded pretty expensive until I learned that you apply it by the teaspoon. Phew, not so pricey after all!)

I learned about mycorrhizae (pronounced “my ko RYE zay”) in my master gardener training. They are fungi, normally found in the soil, that have a symbiotic relationship with vascular plants. The fungi break down minerals (such as the rock fertilizers we use), turning them into ions that can be absorbed by a plant’s roots. Also, the hyphae (fungal “roots”) extend much farther into the soil than the plant’s roots do, and so are able to absorb more water and nutrients which they share with their host. In return, the fungus feeds on sugars produced by the plant. It’s a win-win arrangement.

(If you’re a veggie gardener, you’re probably already aware of bean inoculant. While this is a bacteria, not a fungus, it works in much the same way… the bacteria live in nodules on the roots of beans and peas, taking nitrogen from the air and making it available to the plants. The effect is dramatic, resulting in significantly larger harvests.)

Well, since that training over a decade ago, this has been a hot topic among researchers. It was once thought that only a few plants hosted these beneficial fungi, but now we’re learning that it’s the norm, not the exception. Remarkably, all those claims in the catalog are just the tip of the iceberg.

According to Fred Davies at Texas A&M, plants grown with mycorrhizae are more efficient at absorbing water and nutrients from the soil. This means we need to provide less water and fertilizer, and the plants are more drought resistant. They are also able to fight off soil-borne diseases, and can even reduce the levels of petroleum and heavy metals in contaminated sites! The plants are healthier, too, and less subject to stress. Thus, they are less attractive to insect pests, establish faster after transplanting, and grow faster.

After reading all these glowing reports, I wanted to rush right out and buy myself a fungus. Turns out, it may not be that simple.

Mycorrhizae are part of a complex system involving the make-up of the soil, the plants present, climate, and interference by us gardeners.

As I mentioned earlier, native soils come equipped with all the fungi that the native plants growing there need. The problems come when we alter the environment, either by growing different plants or by disturbing the soil. Highly disturbed soils, and sub-soils such as are found in new housing developments, are particularly lacking in all forms of soil life, including mycorrhizae. Research suggests that yearly tillage on cropland (and perhaps even in a veggie garden?) also reduces the amount of mycorrhizae. Re-inoculating these soils will have a larger impact.

Also, once size does not fit all. Different kinds of plants each have their own specific kind of fungus. This is where I got confused. How do you know which product to buy? And how can they offer just one option when we grow so many different kinds of plants?

The explanation from one company’s website helped answer my questions:

This product contains a blend of eight top types of Endospores – Glomus aggregatum, G. clarum, G. deserticola, G. intraradices, G. monosporus, G. mosseae, Gigaspora margarita, and Paraglomus brasilianum. … This is a general-purpose inoculant for all Endo-dependent plants, including most vegetables, grapes, fruit trees, berries, turfgrass, and flowers.

So… this skeptic is willing to become a believer, but I’d first like some testimonials. Has anyone else tried this? What are your gardening conditions? Could you see a difference?

Photo: via Wikipedia Commons

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