Good fungi!

Do you cringe when you hear the word “fungi?” Probably not if you love mushrooms, but sometimes we have a “that must mean disease” reaction to the idea of tiny microorganisms working away, seemingly out of our control.

But of course, as gardeners or landscapers, we have at least a little control over the soil fungi in our gardens, and we probably already have an idea that some fungi are beneficial. Without a healthy, diverse fungi population (along with lots of other life forms), our soil won’t support plant life, no matter how much synthetic fertilizer we add or how many weeds and pests we kill.

Important in that diversity is a type of fungi called Mycorrhizae. This fungi helps plant roots absorb and make use of nutrients, improves soil structure, impedes weed species from thriving, helps plants withstand drought and decreases soil erosion. “Arbuscular Mycorrhizal fungi” (also known as AM fungi) are the most common type of Mycorrhizae.

While some plants don’t need AM fungi, others seem entirely dependent on some population of the fungi to survive. It used to be thought that native plants were more dependent on Mycorrhizae, but now authorities are beginning to realize that what is important to plants are “their own” Mycorrhizae. California native plants prefer California native AM fungi; plants from Midwestern prairies prefer Midwestern prairie AM fungi. So, plants that originate in the Southern Sierra or Central Valley prefer Mycorrhizae from Southern Sierra or Central Valley soils. Although, it is not an entire waste of money to add store-bought Mycorrhizae, your native plants will do best with fungi already in native soils. Most native soils will have some AM fungi, and it can be just as successful to encourage and support already existing fungi as it can to add more or “foreign” AM fungi. It is not known yet if store-bought “foreign” AM fungi do any harm or are in invasive in native soils.

Soils that may need addition of AM fungi are disturbed soils, because tilling and livestock grazing destroys Mycorrhizae. Fill soil brought into a site is highly disturbed and be very low in AM fungi. You can have your soil tested to see the AM fungi level, but soil that has not been disturbed in the past several months probably has some local, native AM fungi present. Mycorrhizae are most effectively stored on plant roots, so as roots spread into “new” soil, the fungi spread along with them. When plant roots intermingle, AM fungi are spread from one plant to another. Some plants are better hosts, that is they support and store greater populations of AM fungi, than others. In California, restoration projects have identified Tarweed (Hemizonia), Golden Yarrow (Eriophyllum confertiflorum), Goldenbush (Isocoma), and Brittlebush (Encelia californica) as superior AM fungi hosts. In gardens, these are sometimes considered weedy plants, but it may be worthwhile to allow some of these plants in your landscape for their fungi benefits. There is a long list of California native species that support (and rely on) Mycorrhizae that are more common for landscape use. The list includes many tree species (willows, pines and oaks among them),Vitis (grape) and Rosa (native rose). Diversity seems to be important, so planting a garden with a wide range of species, rather than just the subdivision-typical three or four, seem to be important in creating and sustaining AM fungi-rich soil.

Another important way to support a healthy population of AM fungi is to allow or add plant litter on  the soil surface. This means organic mulch. Again, the greater diversity of types of organic mulch, the greater benefit. Added bark, plus your garden plants’ own leaf and twig litter will, over time, support populations of beneficial organisms of all kinds, including AM fungi. The benefits of mulch in regulating soil temperature and moisture help fungi thrive, and as mulch breaks down it provides nutrients and compounds that support beneficial bacteria that AM fungi use.

If you add purchased Mycorrhizae, don’t expect instant results.  Mycorrhizae fungi take six-to-eight weeks to establish themselves on plant roots. In a soil with good populations of AM fungi, plant roots grow first and then the foliage and flowers grow. This is one reason why I am happy to see a new planting of native plants that seem to “sit there” for weeks after planting. The plants look healthy, they’re just not growing—apparently. When I see this, I have evidence that the plant roots are growing and establishing themselves, with the help of beneficial organisms like Mycorrhizae fungi, and we will see healthier, more vigorous plants over time, and plants that can better withstand freezing and high heat.

Healthy soil is one that is alive with many organisms and, over time, requires no additions. Instead, native plants, along with what they shed, supply soil organisms with what they need, and the organisms supply the plants with all that they need. This is symbiosis, and should be the goal of anyone  wishing for a healthy, low maintenance garden.    

Peyton Ellas lives in Springville and is the owner of Quercus Landscape Design, specializing in California native plant-based and eco-habitat gardens. Read her blog and contact her at: www.QuercusLandscapeDesign.com.