There is a good reason why stevia is commonly known as sweetleaf. Its dried leaves are 10 to 15 times sweeter than sugar and a glycoside extracted from the leaves is 300 times sweeter than sucrose. If you grow your own stevia, dry and crush the leaves before using as a sweetener.
In its native South American environment stevia will grow into a small evergreen shrub, but in cooler climates it behaves like an annual. Stevia is finicky about soil drainage; excess moisture, especially right after planting, is the kiss of death. The roots are shallow, so apply a layer of mulch or compost on top of the soil to protect keep them from drying out. Stevia is not cold tolerant below 45 degrees F, so plant it in late spring or early summer when all danger of frost has passed. Water lightly and frequently, allowing the soil to dry between waterings.