The next spring, plants struggled, and I realized I had added too much. Planting cover cropsPlanting cover crops for vegetable gardens is just another way to get food into the garden soil. The cover crops halt soil erosion, reduce weeds, retain water and provide cover for beneficial insects. As a general rule of thumb, most cover crops require a minimum of four to eight weeks of growth before a killing frost arrives. At the end of the season, that means he’s planting cover crops.