Although stevia looks like an average green plant, it is an exciting choice for the herb garden because of the natural, calorie-free sweetness found in its leaves. Appreciated by diabetics and dieters, stevia requires full sun and well-drained soil. Leaves are sweetest in the cool temperatures of autumn. They also taste best prior to the plant blooming. To preserve and to make stevia convenient to use, dry it. Cut whole stems and then strip the leaves and tender stem tips. Place these on loosely woven fabric or non-metal screening outdoors on a dry, sunny day. One day should be long enough to dry the leaves; be sure to bring them in before the dew dampens them again. Once the leaves are crisp, crush them by hand or powder them with a food processor.