Agriculture Reference
In-Depth Information
Mycorrhizal Fungi
Over 95% of plant species form symbiotic relationships with mycorrhizal fungi. The
fungi provide nutrients and water to their host plants in exchange for carbohydrates and
other goodies. In fact, plants will trade as much as 80% of their carbohydrates with these
fungi and other microbes. Mycorrhizal fungi greatly improve soil characteristics, and are
among the most important microbes that form relationships with plants.
This is another of those microbes that should be in our soil, but often isn't anymore. In
soil that has been tilled, compacted, water logged, treated with chemicals, or left without
plant cover, mycorrhizal fungi may be seriously lacking. They aren't present in imported
topsoil or potting soil mixtures either, and don't multiply in compost. In any of these scen-
arios, microbes need to be added back to the soil, especially when planting or seeding, as
they're essential for optimum plant health.
We can inoculate our plants with mycorrhizal fungi by taking just a small bucket of soil
from a healthy environment that contains the right fungi, or by buying a product from a
garden center or online. While the first method sounds like more fun to me, I've always
gravitated to the second because I know what I'm getting.
There are two main categories of mycorrhizal fungi. Over 90% of plants form relation-
ships with endomycorrhizal fungi, also called arbuscular mycorrhizal (AM) fungi. You
need them for most of your vegetables, grasses and many ornamentals. About 5% of plants,
including many conifers and some deciduous trees, form relationships with ectomycorrhiz-
al fungi. When you're planting a mix of plants, you can often buy a mixture of endo/ecto
fungi and just use that for everything.
There are some plants that generally do not form relationships with mycorrhizal fungi.
The most important for vegetable gardeners is the Brassicaceae family: broccoli, Brussels
sprouts, cabbage, cauliflower, collards, kale, mustard and rutabaga; and members of the
Amaranthaceae family: beets, swiss chard, lambsquarters, quinoa, spinach, purslane and
amaranth. The Ericaceae family: rhododendrons, blueberries and cranberries forms rela-
tionships with a different kind of mycorrhizal fungi that can be difficult to find for pur-
chase, but it is out there.
The best time to apply mycorrhizal fungi is at the nursery during the plant production
stage, but since your plants probably didn't have that done, the next best time is at planting/
seeding/sodding. This will allow you to establish contact between the fungi and plant roots,
which is important because that's where the relationship occurs. There's no benefit to foliar
feeding with mycorrhizal fungi, as they need to touch the roots. We can, however, mix
them with biostimulants before application. This inoculant shouldn't need to be applied
more than once, unless other factors are harming them.
