When I started growing native plants I was unaware of how important a certain class of soil fungi were to the growth and even survival of most species. Mycorrhizae (myco for fungi, rhizae for roots) grow in association with the roots of over 95% of the world’s plants, basically serving as “root extenders”. They can greatly increase the effective root area of a plant, accessing water and nutrients in exchange for photosynthate from the host plant. There are two main types of mycorrhizae found with our natives. Ectomycorrhizae you can see growing as white filaments on plant roots, are associated with conifers and some hardwood trees like oaks and birches, and have familiar fruiting bodies (mushrooms, puffballs, truffles). Endomycorrhizae are far more common, associating with 90% of all species; they grow within roots and can’t be seen without magnification. Interestingly, many successful weedy species, annuals that quickly move into disturbed sites like mustards, are not mycorrhizal.
But I’ve resisted having anything to do with them in the nursery. Commercial mycorrhizal inoculant is available, generally as a mix of many species of fungi. After years of skepticism and inquiries, I trialed the use of inoculant last year on a range of species. Growth benefits did show up on several native species, even with all the food and water I was already giving them. The growth advantage should be even greater once they are outplanted in restoration sites where, with little or no irrigation and our low nitrogen, low organic matter soils east of the Cascades, the mycorrhizal help can be the difference between survival and death. If you want to see what mycorrhizae can do, try growing onions with and without them; it’s amazing!