Stevia is a leafy, perennial plant from South America, cultivated globally as a food and beverage sweetener. The processed sweetener from the plant is up to 400 times sweeter than table sugar. Changes in 2009 from the U.S. Food and Drug Administration have altered the status of stevia, allowing it as a safe ingredient in food products, opening the door for commercial cultivation in the United States, as well as for home growing.
Propagation
The University of Kentucky Extension Service recommends propagating stevia plants by using either tissue cultures or rooted cuttings started in a greenhouse. Transplant small, well-established plants outdoors. Stevia can also be propagated from seeds, although the seeds tend to germinate poorly. If propagating stevia from seed, start the seeds in a greenhouse prior to planting. Place several seeds within each cell in the seed tray and thin the seedlings to just one per cell once the seeds sprout. Transplant the seedlings outdoors in seven to eight weeks.
Culture
Stevia plants grow best in soil that is rich in organic material and drains well. The plant will not tolerate wet conditions or soils with high levels of salt. Consistent watering is important, even though the plant is fairly tolerant to drought conditions. Frequent, shallow waterings are best. In rich soil environments, applications of fertilizer are typically not necessary, as the stevia has low nutritional requirements. Excess nitrogen in the soil, particularly from fertilizers, can produce excessive plant growth, resulting in a poorly flavored product.
Pest Control
While stevia plants do not have any significant insect pests, there are some insects that can diminish crop volume. Aphids, white flies and thrips can attack young stevia plants in green houses. Judicious use of insecticides can help control infestations. Also, Septoria diseases may cause damage to plants that are overly mature. Currently there are very few herbicides registered to control weeds around stevia plantings. Mechanical cultivation or hand removal of weeds may be required.
Harvest
When blooms begin to form in late summer, stevia is ready to harvest. The sweetening power of the plant increases as temperatures become cooler and days grow shorter. Complete harvesting of stevia prior to flowering, as the sweet taste of the plant declines once the plant has bloomed. Harvest the plants using mechanical or hand picking by cutting the plants at ground level.
Processing
Dry the stevia in a kiln or other dry environment for one to two days. Once dried, strip the leaves from the stevia plants and crush them thoroughly. Store the leaves in sealed plastic containers. The leaves will keep for an extended period in this condition. For home processing, crush the leaves to a fine powder and use directly as an ingredient in foods or beverages. Alternately, make an extract of the leaves by soaking them in water for several days, then strain the leaves and save the liquid for use in food and drink items. Chemical processing of stevia to isolate the constituents for use as commercial artificial sweetener requires industrial-level processes that are often patented.
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