Now’s the time to enrich your garden beds with cover crops

The gardening season is winding down, the days are getting shorter and the nights are getting cooler. After a busy spring and summer of planting, harvesting, weeding and fighting that endless war on pests, it’s time to take a gardening break, or is it? Allowing your garden to sit fallow during the winter means you are missing out on an opportunity to improve your soil.

Master Gardener Rich M. spreading the cover crop seed in our Learning Landscape

Garden soil can be abused during the growing season from tilling, weeding, harvesting, and foot traffic. One of the most important things a gardener can do to improve the soil is to add organic matter in the form of compost, manures or other organic materials, such as leaves, straw, or grass clippings. Earthworms, bacteria, fungi, nematodes and other forms of life utilize the organic matter to build a healthy soil. Planting cover crops is an economical and easy way to improve overall soil quality.

Cover crops are fast-growing plants that are grown from seed during the fallow times in the vegetable garden, often in fall and winter. Instead of being harvested, a cover crop is grown to provide vegetative cover for the soil.  It can be left on the surface as mulch or tilled while it is still green into the soil, becoming a “green manure”.

Cover crops are easy to plant and require only basic care to thrive. The key is to allow adequate time for the crop to grow, cut it before it flowers to prevent self-seeding and taking up the very nutrients that need to be replenished in the soil, and allowing adequate time for it to decompose before planting the intended crop. Cool-season cover crops are usually planted from late September through late October. Locally, Lockhart Seeds is a good source for finding cover crop seeds. They carry a pre-made cover crop blend that would work well for most home gardeners.

Our 2016 cover crop did very well!

Cover crops have a place in the home garden regardless of garden size and provide many benefits including:

Soil erosion
The roots of a cover crop stabilize the root zone or surface of the soil, reducing the risk of erosion from wind and rain. The leaves and stems of the cover crop also decrease soil erosion by reducing the impact of rain and potential runoff.

Soil Compaction
Cover crop root systems can be used to combat both shallow and deep compaction. Cover crops with taproot (forage radishes) reach deep into the soil and can break up compacted soil layers. Likewise, the extensive root systems of grass cover crops (cereal rye) reduce surface compaction making it easier for vegetable roots to access essential water and nutrients that may previously have been unavailable.

Soil organic matter
Cover crop residues increase soil organic matter, providing numerous benefits to the soil and successive crops. Increasing organic matter improves soil structure, soil water holding capacity and infiltration, and soil aggregate stability.

Weed Suppression
Cover crops can provide weed control by out-competing weeds for light, water and nutrients. Research has found that cereal rye also exhibits an allelopathic effect on weeds, i.e., acts as a natural herbicide.

In general, cover crops are divided into two major categories: legumes (pea family) and nonlegumes (grasses and grain crops).

Legumes include peas, Fava beans, clovers and vetches and are generally grown for their ability to capture nitrogen and make it available to plants. Specialized bacteria on the roots of legumes take nitrogen from the atmosphere and “fix” the nitrogen in nodules that the bacteria create on the roots. In order to ensure that this fixation occurs, and that maximum growth takes place, it is important to attach the bacteria to legume seeds before planting. So when purchasing seeds, also buy an “inoculant” that contains the bacteria.

Nonlegume crops are small grains and grasses such as cereal rye, wheat, oats and barley. Nonlegume crops are generally planted to protect the soil from erosion, add organic matter to the soil, and suppress weeds. They do not have the capacity to add additional nitrogen but will scavenge nutrients such as nitrogen and phosphorus and prevent them from leaching out of soil. When the green material is tilled into the soil, the green manure is broken down and nitrogen, phosphorus and other trace elements become available for use by future plants.

Regardless of garden size, cover crops provide an easy, economical way to improve soil and guard against erosion. In addition to the benefit of improved production from improved soil, a garden that is filled with green in mid-winter is much more appealing to the eye than a bed of winter weeds or bare soil!

For more information about cover crops or other gardening-related questions, call the UC Master Gardener office at 209-953-6112, or visit our website at


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