Prepare soil for spring with a cover crop now
Even though daytime temperatures remain warm, the fall, with cold nights and shorter days, finds many of us pulling out spent summer vegetable plants. What to do with our now bare beds or boxes? Consider planting a fall cool- season cover crop.
Soils are living systems, and many farmers and vegetable gardeners plant cool-weather cover crops for the benefit and protection of the soil.
Cover crops are usually composed of a mixture of annual plants such as grasses and legumes like those often seen in vineyards between the vine rows.
Some examples of commonly used plants are grasses like oats and triticale, annual plants like daikon radish and legumes like vetch, fava or bell beans, annual clovers and peas to capture nitrogen in the air via root nodules.
Some people include spring blooming wildflowers to provide nectar and pollen for beneficial insects and pollinators.
Each plant type provides a different benefit to the soil and above-ground environment and is usually tailored to the specific growing conditions and goals of the garden, farm or vineyard.
Cover crops benefit the soil by physically protecting it from erosion from rain or running surface water. When the stand is robust, these multi-purpose crops can out-compete weeds. Plant roots also help prevent and break up compaction.
Another critical benefit is increasing the organic matter levels in the soil. Many native soils in California have low levels of soil organic matter (OM) — only about 1%.
Our vegetables grow best with OM levels of about 6%. Both the roots and top growth of cover crops, particularly grasses, which are extensive and strong, create large amounts of organic residue that decay over a long period of time.
This increases organic matter levels and fuels soil biology, essentially feeding soil organisms that cycle nutrients and help develop good soil structure.
Plant roots and soil organisms both need oxygen just as much as we do, and well-structured soils are well oxygenated.
A diversity of plants in a cover crop mix helps create an environment that supports a diversity of soil organisms. The roots and decaying top growth essentially stimulate and feed soil life.
With sufficient amounts of organic matter, each teaspoon of soil has or should have hundreds of thousands of numbers and species of bacteria, fungi, actinomycetes and other microorganisms.
These organisms essentially hold nutrients like nitrogen and phosphorus in their bodies or cells, and when they die or are eaten, it is released over time.
Cover crop mixes increase the variety and supply of nutrients in the soil. Some initial recent studies show higher nutrient levels in food crops grown in soils enriched with diverse cover crops.
Plant roots also capture and essentially hold nutrients and prevent water soluble nutrients leaching into groundwater.
The roots and residues of the cover crop and action of the soil organisms improve the soil structure, or aggregation (think of a good piece of chocolate cake) and enable better water filtration into the soil.
The decayed organic matter holds water like a sponge, increasing the water storage capacity of the soil, decreasing needed water use and enabling plants to better withstand drought — an important issue in our area.