Cover crops are highly beneficial in vineyards, orchards and vegetable gardens.
Many people are probably familiar with the idea of cover crops, having seen them planted between the vines in many vineyards, particularly the iconic mustard. In our area, usually annual plants such as grasses and legumes are used to protect and benefit the soil and the health of the crop plants. Some examples are grasses like barley, oats and triticale, and legumes like vetches, fava beans, clovers and peas.
Grasses serve to add a large amount of long-term soil organic matter and legumes act to fix nitrogen in soils. Other plants used or naturalized are mustard and radish, often in heavy soils. Sometimes annual wildflowers are included for pollinators and beneficial insects. Each plant or group of plants has specific roles to play for the crop, the soil, and the above-ground environment; the mixes used are based on the goals of the farmer.
Cover crops protect the soil from erosion, increase the soil’s organic matter, help develop good soil structure, add fertility for the crop plants, and often foster beneficial insects or pollinators. They are usually managed with equipment, but have equal application for our own vegetable gardens, both small and large. There are ways to easily manage them without a tractor.
An important benefit of cover crops in our climate is the protection they provide the soil from erosion from winter rains. They do this by breaking down leafy matter, which in turn breaks the force of raindrops, dispersing them and the flow of water. But they also serve the important function of physically holding the soil with their roots.
Cover crops help develop good soil structure and porosity. Soil texture is the mineral (nonliving or inorganic) component of the soil: the proportion of sand, silt and clay. Soil structure is basically the process of soil particles aggregating into complex structures composed of both solid and pore space (think of the structure of chocolate cake). The pore spaces are places where water and air infiltrate, and soil organisms live. Soils with good porosity readily absorb water. Soils with a high organic matter content hold it, increasing plants resistance to drought. Soil organisms — large and small — cycle organic matter into forms plants can take up.
A healthy soil has around 8-10 million micro-organisms living in each tablespoon of soil. They need organic matter and root exudates — protective organisms in the soil around a plant’s root structure — to feed on. Cover crops provide them with both. Soil structure is created through the interaction of plant roots, soil organic matter, soil macro and microorganisms and soil fungi.
Cover crops can add greatly to soil fertility. Legumes like clovers, peas, beans and vetches, fix nitrogen from the air with bacteria on root nodules. The organic matter provided by both the roots and top growth is cycled into nutrients plants can take up by soil organisms.
A cover crop mix of grasses and legumes is the best to gain the dual benefits of better soil structure, soil fertility and for beneficial insects. A diversity of plant roots leads to a diversity of soil organisms, which studies show are highly beneficial to our soil and plant health. Clovers and vetches are very important plants for pollinators.
A commonly sold and used mix of seeds is called Plowdown mix. It is composed of oats, bellbeans, vetchs, clovers and winter peas.