Mighty Mycorrhiza – Super soil staple or snake oil scam?
By
Amy McDowell
Promises, promises. We’ve all heard
advertisements making promises about some amazing new product and what it can
do for our homes, our lives, our gardens. A healthy spirit of skepticism has
become part of our nature.
So what is the scoop on mycorrhiza? At least
25 mycorrhiza products are available in garden centers across the U.S.—oddly
named products like Myke and Myco Stim to name just a couple. What are these
products, and what will they do for your garden?
Mycorrhiza is a beneficial relationship
between plants and fungus. “Mycorrhiza is a natural part of the soil and a part
of plant nutrient uptake,” writes Ted St. John, Ph.D. in The Instant Expert
Guide to Mycorrhiza, 2000. “The fungi are the dominant soil microorganisms,
and soil biology depends heavily upon the presence, density, and types of
mycorrhizal fungi.”
Mycorrhizal fungi are easily destroyed when
the plants are removed and the soil disturbed. “They are always missing from
freshly graded sites,” St. John writes.
Adding mycorrhizal fungi spores to your soil
(called inoculating) will not necessarily produce big, robust plants, as many
of the products claim. Being familiar with soil biology, I was thrilled when
companies began packaging micorrhizae for home gardeners. In recent years I’ve
tried several of the products in my garden without noticeable results. Although
there are greenhouse and field studies that show amazing differences in plant
growth, I’ve learned that it’s unlikely that you would notice differences like
that in a trial in your own garden.
“Plant growth response in itself is not
likely to tell the story. If uninocculated plots have been kept healthy by
fertilization, any mycorrhizal effects will have been masked,” St. John writes.
Realistically, you can expect inoculated
plants to be stronger, better able to survive harsh weather conditions, and
protected from disease. Your site will be more resistant to invasion by weeds
and most important, mycorrhiza will improve soil structure.
St. John recommends looking for a
“propagule” or spore count on the label so you know what you are getting for
your money. Mix the micorrhiza product with seeds as you sow or apply it to all
sides of the root ball as you put plants in the ground. You can sprinkle
mycorrhizae over the surface of the soil or till it in, but it doesn’t begin
working until it connects with live plant roots.
Although he warns gardeners to be wary of
hype and exaggerated claims, St. John solidly backs mycorrhiza as beneficial
for gardens. “What is very clear, from every study that has done the tests, is
that inoculation is greatly superior to no inoculation,” he writes.
