Northern Virginia Soil and Water Conservation District

703-324-1460 TTY 711
12055 Government Center Parkway
Suite 905, Fairfax, VA 22035
Willie Woode
Executive Director

Cool Season Cover Crops for Better Soil

By Willie Woode, NVSWCD Senior Conservation Specialist

Here’s hoping you had a great gardening experience this year! Sooner rather than later, the weather will get colder and garden plants will yield to the cold temperatures. Most people may think, “It’s time to let the soil rest!” Actually, because soil is a living entity it does not need to rest. Rather, it needs to be kept active so that all its millions of microbes can continue to stay alive through the winter months.

To keep your soil active, you can grow a cool season cover crop mix. This practice is recommended because the plant species in the mix rebuild the soil by:
  • Improving soil structure through increased soil microbial activities
  • Increasing water infiltration and water holding capacity
  • Reducing soil compaction
  • Enhancing soil organic matter
  • Recycling plant nutrients
  • Enriching soil nitrogen content
  • Insulating the soil to allow microbes to survive cold winter months
The seeds of cool season cover crop mix are best planted by broadcasting method, about a month (15 – 45 days) before the first killing frost. In Fairfax County, the average date for the first killing frost is October 25.
It is important to remember that cool season cover crops should be tilled into the soil about a month before spring planting, or before they flower or seed. If the cover crops are allowed to flower or seed, accumulated plant nutrients that should be available for your new garden plants would have been utilized in making the flowers and seeds.

If you decide that a cool season cover crop mix is a good fit for your garden, you can purchase the seeds required at any seed supplier. Deep-rooted plants (brassica) reach deep into the soil and draw nutrients back up into the root zone of most plants and legumes (nitrogen fixing plants) convert atmospheric nitrogen into plant available nitrogen. A common cool season seed mix can include legumes (such as snow peas, hairy vetch, and white clover), grasses (such as triticale and annual/winter rye), and brassica (such as rapeseed, turnip, and radish). The basic mix recommended by several Soil and Water Conservation Districts includes triticale, orchard grass, annual ryegrass, black oats, turnips, rapeseed, and white clover. 
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