If you still haven’t selected groundcover plantings for the coming season, that may be a good thing. Because it’s a good time to make sure your choices fit the right stage of ecological succession.
Succession is the phenomenon by which a natural system progresses from one kind of plant-and-microbe profile to the next. If you’re an orchardist, you’re aiming for later-successional soil conditions. Vegetables? Early- to mid-successional. Grasses? Mostly early-successional. Every plant type is at home somewhere along the spectrum, which means your understory plants – so important for microbial health and overall soil condition – need to match the ecological stage you need for your target crop.
We talk a lot about the phenomenon of succession around here, because it’s key to biological soil management. To recap: after a soil is disturbed – by something catastrophic like a violent flood, or landslide, or plowing -- microbial populations are largely destroyed. As bacterial communities gradually begin developing again, shorter grasses begin growing, feeding on the particular nitrogen-based compounds that those bacteria produce. After many years, taller grasses may rise to dominance; then shrubs and vines, then trees. As the pattern progresses, different types of soil fungi begin proliferating, so that eons later, barring any further disturbance, towering trees might be found thriving in soil that harbors many times more fungal biomass than bacterial.
Clover has long been popular as a cover crop among commodity growers because it is nitrogen-rich, and therefore can be treated as an organic fertilizer to be tilled under at maturity. But clover can also be a good choice from a soil-biology perspective. There are various types, of different heights, both annual and perennial: as such, they match up with biological profiles exhibiting a fungal-to-bacterial ratio anywhere from 0.5 to around 2.0. This means clover can accompany grasses like corn, various field and row crops, and even some vines and trees.
If your aim is to develop soil toward a later-successional stage appropriate for vineyards and orchards, go for perennial varieties – whether clover or other plants types, like ground-hugging vines, or hardy landscaping plants like dichondra. Perennials develop woody materials, which are rich in lignin. They therefore share their successional stage with the fungal species that are capable of digesting lignin; those fungi in turn feed more trees by extracting nutrients from the dead ones.
Because one organism so depends on another, we can help create a quick successional change by introducing plants that belong in that stage. These plants promote the well-being, either directly or indirectly, of all other species sharing their habitat. With proper microbial applications, we can change soil conditions fast; if the right plants are already present, the shift to our target successional stage can happen all the more quickly.
Beyond succession, the best groundcover for your crops will further depend on local conditions, size at maturity, sun exposure, and other factors. The matching of plant varieties is what permaculturists do; if you can find a permaculture expert in your area, they may suggest some good candidates. Another possibility is your local native-plant group (around here we have the California Native Plant Society).
It may take some doing to find the plants that work best. But once you do, you have a powerful element of soil management that makes the entire system more efficient. And that means less future investment as your crops keep flourishing.