Fall is the perfect time to think about soil improvement. Though frost may have killed off your tomato plants, and shortened days may have slowed the growth of your greens, it's not too late to sow seeds of soil-building cover crops. The concept is simple: If your soil hosts living roots, summer and winter, it will nourish a healthy microbial community. This is the very definition of healthy soil.

Cover Crops That Survive Through Winter

Winter-hardy cover crops, such as winter rye, winter wheat, vetch, and clovers, generally establish roots and grow through the fall while the soil is still relatively warm. Depending on the region, they continue to grow slowly during winter, or go dormant for a period. Aboveground growth resumes or accelerates in spring. It takes almost no time to sprinkle these seeds on your garden beds after summer crops have died back, and you’ll receive multiple benefits:

It takes almost no time to sprinkle these seeds on your garden beds after summer crops have died back, and you'll receive multiple benefits: 

• They improve the soil structure: Cover crops with fibrous root masses, such as winter rye, loosen the soil as they grow and then decompose. The deep and extensive root structures prevent soil compaction.

• They break the cycles of disease: Cover crops of all types contribute organic matter to the soil. This contributes to increased activity of the bacteria and fungi in the soil, which has been shown to increase plants’ resistance to pests and disease.

• They add fertility to the soil: Plant roots release compounds that support soil microbes, which in turn help plants take up necessary nutrients. A root zone that is active all year round contributes to soil fertility.

• They prevent spring weeds from sprouting: A dense stand of rye or vetch will leave no room for weeds to grow. And when the cover crop is cut down, the residue on the soil surface will prevent the germination of weed seeds.

Cut down your cover crops and incorporate the green matter into the soil two to three weeks before you plan to plant your summer crops.

Cover Crops That Are Winter-Killed

Cover crops such as oats, forage radishes, and mustards should be planted earlier, so that they have time to put on some growth before they die back. In winter, they'll provide a protective layer over the soil and in spring you can transplant seedlings right into the layer, or incorporate the residue into the soil. 

• Oats: In cold-winter regions, plant oats at least 6 weeks before the first frost; they'll scavenge nutrients from the soil, making them available to spring crops. In mild winter areas oats can be sown in fall or winter, and incorporated into the soil in spring

• Forage radishes are an excellent choice if your soil is compacted. Sow the seed in late summer to early fall. They'll grow to about 18 inches, leaving the soil weed free in spring, and perforated due to the long tap roots.

• Mustard cover crops can be sown in late summer to fall for erosion control, weed suppression, and nutrient scavenging. They're known for producing compounds that can be toxic to disease organisms. 

If you've never used cover crops as a soil improvement technique, give it a try. Think of it as a time saver (less weeding in spring) and a money saver (you'll need less fertilizer), rather than another chore for your busy fall.