I use mycorrhizal inoculant in my organic garden almost every time I plant and seed. I wouldn’t plant without it.
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, many plants will trade more than 50% 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 mix either, and don’t multiply in compost. In any of these scenarios, they need to be added back to the soil, especially when planting or seeding, as they’re essential to optimum plant health.
We can inoculate our plants with mycorrhizal inoculant by taking just a small bucket of soil from a healthy environment that contains the right fungi, or by buying mycorrhizal fungi products 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.
Types Of Mycorrhizal Inoculant
There are two main categories of mycorrhizal fungi. Over 90% of plants form relationships with endomycorrhizal fungi, also called arbuscular mycorrhizal 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 ectomycorrhizal fungi.
When you’re planting a mix of plants, you can often buy a mixture of endomycorrhizal and ectomycorrhizal fungi and just use that for everything.
How To Apply Mycorrhizal Spores
The best time to apply mycorrhizal inoculant 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. Mycorrhizal products shouldn’t need to be applied more than once to each plant, unless your management practices are harming them.
Rub the fungi directly on the root ball if possible, or sprinkle in the planting hole.
For seed, mix it dry with the seed before spreading.
For sod, get a powder form of the fungi, mix with water, and spray it on the soil right before you lay the sod, or even better, right on the bottom of the sod. You could spray it on afterwards as well and water it down to the root zone.
While not as good, the other choice is to apply the product to existing landscapes. The powder form is best for mixing with water to get the spores to infiltrate into the soil.
For turf, it’s better to do this right after aerating so more of the spores get down to the roots. Otherwise, it can be watered in, but will not be as effective on heavy clay or very compacted soils.
Vegetable Plants That Don’t Use Mycorrhizal Fungi
There are some plants that generally do not form relationships with mycorrhizal fungi. The most important for vegetable gardeners is the Brassicaceae family:
- brussels sprouts
… and members of the Amaranthaceae family:
- swiss chard
- lamb’s quarters
So that’s the basics of how to use mycorrhizal inoculant. Any questions? Have you used it before? Let me know below.
Or check out my more detailed mycorrhizae article.