I love going to the Garden Writers Association meetings. I get to see other garden writers, editors and photographers. Listen to the latest and greatest in the garden writer’s world. I am, however, ambivalent about receiving goodie bags filled with garden product. The organizers of the GWA meeting emphasized that in exchange for getting these “gifts,” we are obligated to write about them. Some of these products are great, but others…not so much.
I focus my attention on soil-related products (of course!). One of the products being pushed aggressively this year is mycorrhizal inoculant. I received a tub of Myke Tree & Shrub growth supplement as well as a book explaining how mycorrhiza work and their use in horticulture.
I’m not surprised. Although mycorrhizae studies have verified the beneficial affects, the use of mycorrhizal inoculant in the landscape has not fared so well.
Beneficial effects of mycorrhiza/plant association
Nutrient and water exchange between plants and fungi
Increases soil aggregates (a good thing, it improves soil structure)
Enhances organic matter decomposition
Acidifies root zone (which facilitates uptake of nutrients)
Use of mycorrhizal inoculant in the urban landscape
After reviewing the latest scientific research on the use mycorrhizal inoculant in urban landscapes Dr. Linda Chalker-Scott concluded that
“…applying commercial mycorrhizal amendments is generally ineffective and unnecessary, give the widespread presence of indigenous inoculum.”
In other words, your soil already has mycorrhizae. Why waste your money and time adding something that is already there?
Dr Chalker-Scott also noted that generally “plant species inoculated with commercial products and installed into the landscape are equal in performance to uninoculated controls (which quickly became colonized with native fungi).”
It all fairness, adding mycorrhizae inoculant to sterilized potting soil is effective, as long as the containers are not overwatered and overfertilized.
The argument has come up some soils don’t have mycorrhizae, and the addition of mycorrhizae could help. But if the soil is impaired to the point that indigenous mycorrhizae won’t survive, mycorrhizal amendments alone won’t help.
So how do we keep the mycorrhizae in our soil happy?
Stop using soluble phosphate fertilizer (it stops mycorrhizal development on plant roots)
Avoid overwatering and overfertilization (increases the chances of roots being infected by these beneficial fungi)
Reduce pesticide use
Increase the diversity of trees, shrubs, ground covers and perennials in our gardens
Add organic matter (it simulates the growth of native mycorrhizal populations)
Chalker-Scott, Linda. Mycorrhizae. What the heck are they anyway?
Soil Health website. Mycorrhizal associations
For the visual learners
Society for General Microbiology. The New Green Revolution: Arbuscular mycorrhizas