While these plants have been known to overwinter in climates as low as Zone 8, if planting stevia in a colder climate, you run the risk of losing plants to frost. The solution is to grow stevia as an annual, or overwinter the plant indoors.
Be careful when weeding, as the plant’s branches are fairly brittle. Stevia doesn’t have any known diseases or pests. But it would be smart to defend against pests and diseases that plague similar culinary herbs.
At the end of September or beginning of October, harvest the entire plant once flower buds have appeared but before they’ve opened. Ideally, harvest in the morning when the plant is at its highest sugar content. Also, be sure to harvest before many flowers (4-5 buds) have opened. If most of the flowers have blossomed, they will leave behind a bitter aftertaste throughout the entire plant.
Stevia also has several health benefits. Not only does stevia possess hypoglycemic effects when ingested, but it also can help improve insulin production: a benefit that may be intriguing to diabetics. Stevia is a natural antioxidant, helping your body fight against free radicals (molecules that can damage cells, lead to heart disease and cancer, as well as other illnesses). Stevia can help with hypertension, or high blood pressure, and also inhibits the growth of bacteria that can create dental cavities.
Photo: (cc) Gabriela Ruellan/flickr
If you're interested in growing stevia, here are some seed resources: