In my post Befriending Fungi: Part I, I gave a very brief and simplistic history of the symbiotic relationships between mycorrhizal fungi and plants, and how we can benefit from having healthy fungal soil.
Here’s the summary:
- Ninety five percent of all land plants have symbiotic relationships with mycorrhizal fungi, including the majority of food crops.
- Mycorrhizal fungi help plants acquire trace minerals, water, phosphorus, and many soil nutrients. These fungi actually regulate soil resources and will send extra support to struggling plants, enhancing the health of entire plant ecosystems. They also act as an extension of a tree’s root system, allowing them to source water and nutrients farther away.
- Endomycorrhizae (those that actually enter the roots of trees in order to swap resources) stimulate an immune response in trees, releasing phytochemicals which protect the trees against pests and disease, and increase levels of beneficial phytonutrients in the fruit.
- Mycorrhizae produce a protein called glomalin, which increases moisture retention and improves soil structure, as well as sequesters huge amounts of atmospheric carbon.
Also worth mentioning, mycorrhizal fungi can facilitate communication between between plants. If a pea weevil infestation breaks out at one end of a row of peas, fungal connections actually send a message to other plants in the vicinity and those plants elevate their phytochemicals in anticipation of the insect before it even lands on their leaves. AMAZING! So much happens beneath the soil that we have yet to discover and understand. This is just the tip of the iceberg when it comes to the ways fungi benefit all the life around them, and facilitate healthy ecosystems.
But the key message here is that mycorrhizal fungi are organisms you want in your farm or garden. Your plants want to grow with them and will be more resilient as a result. There are many ways to encourage these fungal superheroes at home.
Know what soil fungi like, and don’t like
First off, they don’t like being disturbed. The majority of beneficial fungi are in the top 4 inches of soil. If you regularly till or disturb this top section of soil you are breaking up the fungal hyphae (roots) and killing the mycelium. Shallow tillage by hand or with a power harrow attachment in only the top couple inches of soil can leave those lower layers of mycelium intact so they can move back into the surface while the next crop is growing. Better yet, use permanent beds and apply a no-dig approach if feasible. For deep soil aeration, use a broad fork rather than double-digging or rototilling, as this minimizes disturbance to the soil layers and hyphal networks.
Fungi hate bare ground. Mycorrhizal fungi only grow where plant roots exist, so clearing, tilling, or using herbicides on a field and leaving it bare destroys all hosts for beneficial fungi. In a vegetable or market garden, use cover crops wherever possible, plant your food crops into small clearings in the cover crop and once established, chop-and-drop the cover crop around your food crop. This provides a continuous supply of plant roots and the additional mulch from the cover crop protects the soil and feeds other beneficial fungi. Brassicas and Chenopods are the exception as they don’t associate with mycorrhizal fungi, so if you are using buckwheat or mustard as a cover crop, include some amount of oats or rye in your seed mix to keep fungi levels high. If interplanting with cover crops isn’t an option, having periodic rows of your garden in a perennial crop such as asparagus, herbs, or raspberries so that there is a population of undisturbed beneficial fungi nearby that can move back into cleared and tilled areas.
Wherever possible, apply mulches around perennials that feed soil fungi. Michael Philips, author of The Holistic Orchard and Mycorrhizal Planet recommends using ramial wood chips, the small-diametre prunings of deciduous trees, as the ideal fungi-feeding mulch in orchards. You can learn more about ramial wood chips here. Hardwood wood chips, straw, dried grass, chop-and-drop dynamic accumulators, even cardboard and newspaper, can make great mulches that protect bare ground and help feed soil fungi. There is sometimes concern that adding high-carbon mulches to soil will lock up available nitrogen. If those mulches are applied to just to the surface, then decomposers, bacteria, and fungi can break them down and integrate them into the soil at a rate that keeps soil nitrogen levels stable. Living mulches in pathways and around perennials, particularly clovers, are also great at supporting soil fungi. Plastic mulches, however, are not so good. Even using silage tarps for solarizing, sterilizing soil, and killing weed seeds and roots, will also kill off a lot of fungal spores and hyphae. If you have to use plastic mulches or solarization, reintroducing beneficial fungi into the next crop through inoculating seed, potting mix, or transplants can help bring your soil back to life.
Reintroduce beneficial fungi to your soil
There are many ways to bring beneficial fungi back to degraded or sterilized soil. There are commercial inoculants available as powders you can mix into potting mix or coat seeds, or root-dips for inoculating transplants or bare root perennials. There’s a lot of variation when it comes to quality. Low-quality garden-centre brands might have sat on a shelf for a year and only have a few weak strains of mycelium, whereas high-quality ones will have dozens of strains that are also fresh and more viable.Mycorrhizae growing in and around inoculated plant roots. Photo credit: Mycorrhizal Applications
Keep in mind that different crops have specific strains of mycorrhizae associated with them. Most herbs, vegetables, grasses, legumes, cane fruits, and fruit trees need arbuscular (endo) mycorrhizae (Glomeromycota). Blueberries and their relatives need ericoid mycorrhisa (Ascomycota and Basidiomycota), an entirely different phylum. Many forest species work with ectomycorrhizal fungi (Basidiomycota and Ascomycota). When reading the ingredients, make sure the fungi match what you are planting in that area, and when in doubt go choose a broad-spectrum inoculant with many different strains. There are many studies finding that nursery trees grown in inoculated soil far outperform and have much larger root systems than those not grown with mycorrhizal fungi.