Kickstart your soil mojo with mycorhizal fungi and under cropping
Nature abhors bare soil. Bare soil is constantly losing soil carbon and the fertility associated with it. A garden bed with a full canopy of plant growth is actively increasing the fertility and life of the soil that comprises it.
A cover crop, or “green manure,” is a fast-growing plant that benefits the soil and the general garden ecosystem (for example, by fixing nitrogen or out-competing weeds) rather than serving primarily as a food source. Cover crops for gardeners typically include: clover, buckwheat, peas, annual ryegrass, alfalfa, winter wheat and oats.
Plants dedicate a large portion of the carbon they obtain from the atmosphere into producing exudates—starches and sugars they use to nurse and nurture the communities of microbial allies necessary for good plant health. These masses of microorganisms multiply and flourish, adding to the enduring fertility of the soil.
In Utah, there often simply isn’t enough time to get our cover crop planted (one to two weeks for germination), give it ample time to grow (six to eight weeks), then enough time to reincorporate into the soil after turning it in (two to four weeks). We’d need to plant a cover crop in February in order to be ready to transplant warm weather veggies into the garden by Mother’s Day. I’ve done this many years and found regardless of when I plant, nothing germinates or starts performing well until late March.
Enter some boss level solutionism. I’d like to introduce you to my friend, under cropping: the planting of our cover crop as a living mulch. Under cropping is the strategy of growing cover crops as a supportive understory to the main crop, rather than as an exclusive separate process in sequence. This is a style of interplanting or polyculture, the growing of plants in communities. This is a more accurate representation of how nature do.
The easiest way to adopt this strategy is in the fall. When tall crops such as tomatoes, peppers, and trellised cucumbers are at their peak in late August, I prune away the lower unproductive parts of the plants, lightly rake the exposed soil, broadcast the seeds of a soil-building cover crop mix and cover with a thin layer of compost. The microclimate under the mature plants is perfect for establishing these new seeds and by the time the first frost comes, there will be a glorious carpet of clover (or any other cover crop).
Many species in the cover crop mix overwinter and begin growing again in February. With this massive head start, we are able to turn the cover under in early March and plant spring crops a few weeks later. Or, we can enjoy a massive infusion of organic matter into our garden beds by letting it continue to grow, and still have enough time to turn it under before planting our summer crops.
Another strategy, more appropriate to our current timeline, is to get our cover crop started now and eventually plant our primary summer crop into it. This early planting will get the microbial mojo of your soil kickstarted.
We can take this strategy to the next level and inoculate the cover crop seed with rhizobium bacteria and mycorrhizal fungi spores (available at garden centers and online). The rhizobium will form a symbiotic relationship with the clover, a legume, to “fix” nitrogen from the air to be utilized by following crops. The mycorhizzae will form a symbiotic relationship with the clover to create a complex most easily imagined as super mega roots, which will also be used by the subsequent summer planting.
This boss level strategy has been adopted by large-scale corn growers with an astute ecological savvy, resulting in a dramatically lowered dependence on fertilizer and a near complete suppression of weeds. Next level farming maneuver. But you, in your garden, can do this, too!
While there are a number of significant benefits with this strategy, competition for water and nutrients between our ground cover and our primary crop is a concern. The first strategy is to plant the entire bed with our cover crop selection, then pull or hoe under 12-to-18-inch circles or long strips where our target crop is to be grown. This void can now receive transplants, which will have time to get established without competition, and well ahead by the time the cover fills back in. The cover can then be cut or pulled later in the season and left in place as mulch.
You may choose to simply plant the edges of your beds so that you don’t have to manage for competition later. Because, why work more when you can work less?
James Loomis is a fulltime urban farmer, educator and permaculture hooligan.
About that seed….
Orson Boyce of Utah Seed in Tremonton, Utah says all white clovers are not created equal—some grow quite tall. For under cropping, he suggests Microclover, Aberlasting White and White Dutch.
A little bit of clover seed goes a long way. A mere five ounces (about a third of a pound) will cover 1,000 sq. ft. (that’s a 35 x 40-ft. garden bed). Why not get a whole pound of seed and share with a few garden friends?
While Utah Seed sells by the 50-lb. bag, you can find garden-size quantities of some under cropping clovers at garden centers and True Leaf Market, the retail limb of Mountain Valley Seeds in Salt Lake City (175 W. 2700 South). Several varieties are also available online at Etsy and elsewhere.
Sprinkle it on and rake in lightly. It will germinate in 10-15 days when the soil temperature is 50-60 degrees. You can find your soil’s temperature with an instant-read thermometer made for cooking.