Answer: The timing of your question is perfect - National Gardening Magazine just did an article on stevia that includes all the information you're looking for! The article will appear in the on-line magazine at http://www.garden.org within the next few weeks.
In cold northern areas, it's best grown as an annual, or you can pot up plants to bring inside for use during the winter. In nature it grows on moist, sandy streambanks and marshes, so in the garden, provide a well-drained humusy-loam soil that is slightly acidic (6.0-6.5, which is good for most garden vegetables). Transplants are slow to get going, but will take off in midsummer. Harvest leaves before the plants flower, and dry them for storage. A few days of strong sun should be enough to dry them well. You can try experimenting with propagation with cuttings taken in summer. Dip 3" tip cuttings in rooting hormone and plant in a tray of moist - not soaking wet - sand, and mist frequently. Or try rooting them in a vase of water. Indoor plants require supplemental light and a warm room (70F) during the winter.
You can order plants from these suppliers: Logee's Greenhouses, 141 North St., Danielson, CT 06239, ph# 800/330-8038 - catalog, $3; Oregon Exotics Nursery, 1065 Messinger Rd., Grants Pass, OR 97527, ph# 541/846-7578 - catalog, $4; Richter's Herbs, Goodwood, Ontario, Canada, L0C 1A0, ph# 905/640-6641. Enjoy!
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