Harvest beet greens by pulling them from the soil when they are 4 to 6 inches tall. At this stage, young beets have not yet formed. Wash the leaves in cold water to remove garden soil. Trim away the root tip, leaving the tiny swollen beet attached, as these cook quickly and enhance the flavor of the greens. Cook the greens in your favorite recipe.
Cut the leaves of beet greens near the soil level, if you want to let the beet grow to maturity. Harvesting the tender young leaves does not harm the plant, as new leaves soon grow to replace them.
Harvest the entire plant the if tops have grown tall, with long stems. Cut the leaves from the stems with a sharp knife to use for beet greens. Stems are not edible at this stage, as they have already become tough and stringy. Cook the beets separately, or store them in the refrigerator for later use.