Most grow beets for their roots, but beet greens are also tasty and nutritious. Harvest beet greens when thinning plants and use them in salads. Outer leaves can also be harvested as the plant matures. Beet roots can be eaten when they are about 1 inch across, or can be left in the ground to grow larger. If you want to leave them in the ground for winter harvest, cover with a layer of straw or other mulch.