Every gardener has most likely experienced the bitter-sweet feelings that arise with the changing of the seasons. The cool, crisp air of fall and winter can be such a relief from the seemingly relentless heat of summer here in the mid-south, and the onset of shorter daylight hours leads inevitably to a slower pace. Yet for gardeners, this relief comes with a sad price, for there are few plants that provide the same kind of comfort, delight, and diversity of color and texture in the winter months than in the heart of the growing season. While many may see these months as an invitation to plant a few pansies and ultimately wait patiently until the warmer weather resumes, there are actually other, more sustainable options for gardeners, even for those cultivating on a small scale. One such option, demonstrated in My Big Backyard, the Delta Heritage Garden, and the Butterfly Garden, is the use of cover crops.
For gardeners, nothing is as important as soil. The quality of one's soil determines, in essence, the quality of the plants that are grown.
A healthy balance of nutrients, minerals, organic matter, and drainage is the key for growing healthy plants. Though many commercial farms and ornamental gardens throughout the country rely heavily on chemical fertilizers and inorganic methods in order to replace the nutrients lost or leached from the soils, sustainable, organic solutions, such as the use of cover crops, offer nutrients to the soil, beauty to the beholder, and habitat for beneficial insects. In fact, cover crops have been used for centuries as a means of covering otherwise barren ground and rehabilitating soils.
The concept of cover cropping is simple. In order to replace the nutrients and organic matter lost by heavy cultivation, certain plants and legumes are grown during a period of time, turned back into the soil, and allowed to decompose for a period of time before the next growing season begins. This strategy not only adds organic matter and nutrients to the soil- helping with both drainage and fertility- but it also prevents erosion and nutrient leaching, both consequences of having exposed soil. By using cover crops as a living mulch, the unexposed ground is able to retain more moisture and increase water infiltration while also suppressing weeds and relieving soil compaction. Cover crops are also huge for certain beneficial insects, such as lady bugs. Providing habitat for insects such as these, as well as providing an early pollinator source in the spring, can make all of the difference once the growing season begins.
Though varieties of cover crops can be grown in every season, those demonstrated at the Memphis Botanic Garden were selected and sown as a winter cover. This means that the plants selected, crimson clover, Austrian winter peas, cereal rye, hairy vetch, and mustards, to name a few, are all cold hardy to a certain temperature. By seeding these in late September-early October, the plants germinate and become fairly established before the coldest months begin. Then, as the winter months commence, the crops each grow, albeit slowly, and perform their individual tasks. For legumes such as crimson clover, Austrian winter peas, and vetch, this means taking atmospheric nitrogen, typically unavailable to plant uptake, and transforming it into usable nitrogen in the soil. For others, such as rye and mustards, it means using extensive root systems to hold onto the soil, cover the ground extensively to suppress weeds, and, in mustard's case, even act as a biofumigant. What's more, the cover crops all provide color to the garden when most plants have either gone dormant or died. When the warmer weather begins in March and April, the cover crops that have survived the winter cold will grow at an exponential rate, in some cases even adding lovely flowers that pollinators delight in. If you have experienced the spring blooms of crimson clover, you know that there are few sights as lovely. In early to mid-spring, it is essential to plow, or turn, the cover crops over so that they have time to begin decomposing before the warm growing season begins. With the additional nitrogen 'fixed' in the soil from the legumes and all of the nutrients added as the cover crops slowly break down in the soil, the soil will be teeming with microbes and replenished enough to begin another bountiful year of growth.
By David Vaughn, MBG horticulturist
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