I really had no idea about the concept of cover crops when I lived in the Mid-west. But out here in the Pacific Northwest one organic practice that was highly recommended to me is cover cropping after the fall harvest. Once the rainy season begins, soil gets compacted and many nutrients, such as nitrogen get washed out of the soil. The idea is to not leave bare ground during the rainy season. Roots keep air spaces and when you dig the plants into the ground a few weeks before you want to plant again, the nutrients return to your garden.