Q: I was wondering if you had an opinion on mycorrhizae? I’m thinking of buying some to use when planting trees and other things.
A: Mycorrhizae are beneficial soil fungi. They associate with plant roots and bring them moisture and nutrients in exchange for sugars from the roots. I think the jury is still out on whether adding mycorrhizae is beneficial when planting trees. Soils with typical amounts of organic matter contain mycorrhizae naturally. Adding more, in my view, doesn’t make sense. On poor soils (solid clay, very sandy, etc) mycorrhizae might be beneficial. For now, I simply recommend adding organic matter when planting shrubs and vines. When planting trees, the most important stimulus seems to be loosening the soil in a wide area around the planting spot.