Mycorrhizal Inoculants – Help or Hype?

v1764While I was exploring what mycorrhizae are, I found that they’re available not only in potting mix. Park Seeds sells “Myco Blast” which is touted as a probiotic for your plants – the plant version of Bifidus Regularis®  in Activia yogurt! Territorial Seeds has “Myco-Edge Endo Myco.” I typed “mycorrhizae” into Amazon and found all sorts of mycorrhizal supplements.

All of this made we wonder if I’d missed an important component of gardening for all the years I’ve been growing plants. Is this the new frontier of gardening? Do I need to get these formulas in order to grow a good garden?

After exploring it, I’ve come to the conclusion, that for me, the answer is no!

(The only plants for which mycorrhizae are necessary for their survival are trees and shrubs that have endomycorrhizae such as pine trees. If you purchase a pine tree to plant in your yard, it already has the necessary mycorrhizae or it wouldn’t have grow to the size of a transplant. Also all of the inoculants that I found for sale were for ectomycorrhizae.)

A lot of organic gardening sites purport that tilling of the soil and the use of inorganic fertilizers and various pesticides have reduced the amount of zygomycete spores in the soil and therefore limit the number of mycorrhizae that can form in plants. That might be true though I have to admit that I have a some doubts about this claim – fungi spores are not only ubiquitous but also tough. I have a hard time believing that the ones that produce ectomycorrhizae don’t already exist in most soil.

But there are other reasons that cause me to question the use of these various formulas of “mycorrhizae.”

The first is that a number of common plants in the vegetable garden don’t form mycorrhizae even if the soil is full of zygomycete spores. Plants of the goosefoot family (Chenopodiaceae) and cruciferous plants (Brassicaceae) never form mycorrhizae. For me, that’s a large part of my vegetable garden, including spinach, beets, chard, broccoli, cabbage, radishes and more. Using a mycorrhizae inoculant on these plants will do nothing because they don’t form mycorrhizae.

But the biggest reason why I don’t think I’ll be using these products is because of something that research has found. Mycorrhizae help to extract water and nutrients from the soil and are particularly helpful when the soil is marginally fertile. But it’s been shown that plants which in the wild form ectomycorrhizae don’t form them if the soil is fertile.

That makes perfect sense. This mycorrhizal symbiotic relationship does cost the plant some energy in the form of carbohydrates that the plant provides to the fungi. When fertility is low, this cost to the plant is offset by the benefit of nutrients that the fungi are able to extract from the soil (particularly phosphorus). But when the soil is fertile, mycorrhizae offer the plant no benefit so they don’t form.

I fertilize my vegetable and flower beds so there’s plenty of nutrients in the soil for the plant to absorb. The odds are pretty good that even if I added mycorrhizae inoculant, mycorrhizae wouldn’t form because the plants don’t need it. Also most of the plants that grow in the vegetable and flower garden aren’t bred to live in marginal conditions where mycorrhizae show their greatest benefit. They grow best in fertile soil, the very conditions that limit the formation of mycorrhizae.

If I was planting a field of wildflowers that I never planned to fertilize – a native, natural garden – it might be of benefit to add one of the mycorrhizae inoculants to the soil. But then again, there would probably be all of the necessary fungi spores already in the soil.

All of these mycorrhizae products certainly don’t hurt anything and they might help. They’re also fairly inexpensive so it won’t break the bank to give them a try. But I can’t help but think that a lot of the so-called benefits from these products are little more than the placebo effect. You can say you added mycorrhizae to the soil and your plants grew better but without a microscope you can’t see the mycorrhizal associations so any “benefits” from these products can’t be proven to be the result of mycorrhizae.

I might learn more over time that’ll change my mind but for now, I’m glad to know about mycorrhizae but I don’t think it’s something with which I need to concern myself in the vegetable and flower garden.

I’d rather spend the money that these mycorrhizal products cost on good fertilizer to boost the fertility of the soil. I know that’ll benefit my plants!


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s