If you enjoy gardening, Stevia can be a rewarding herb to grow. While it's not feasible for most of us to grow sugarcane or sorghum in our backyard, several Stevia plants will fit nicely into a small garden. Recipes utilizing Green Stevia Powder are now available, and the whole leaves add to the flavor of herbal teas.
Stevia rebaudiana is a tender perennial, native to semi-humid subtropical regions of Paraguay and Brazil. Wild plants occur on acid soils that are constantly moist, but not inundated, often near the edge of marshes or streams where the soil is sandy (Brandle et al., 1998). In the garden, too, Stevia doesn't like to dry out, but standing water will encourage rot and disease. Stevia can be a successful garden plant in most climates with the use of a few simple techniques. Raised beds or hills prevent "wet feet," while an organic mulch and frequent watering ensure a constant supply of moisture.
In North America, Stevia survives winters only in the warmest areas such as southern California, Florida, and Mexico. Research in Japan indicates a critical winter soil temperature of 32 F to 35 F (Sumida, 1980). Stevia is a weak perennial, so plants grown as perennials should be replaced every few years. In colder areas, Stevia is planted after the last frost and treated as an annual. Longer summer days found at higher latitudes favor leaf yield and Stevioside content (Shock, 1982).
While tolerant of most soil types, Stevia prefers a sandy loam or loam. Any well-drained soil that produces a good crop of vegetables should work fine. Incorporating organic matter is the best way to improve heavy, high clay soils. A rich compost made with leaves, grass, hay, kitchen waste, manure, and other organic residues will improve soil structure and supply nutrients. Finished compost may be tilled, disked, or spaded into the soil before planting or used as a mulch later on. A "green manure" crop the previous year such as oats, rye, or legumes will also improve heavy soils. Stevia occurs naturally on soils of pH 4 to 5, but thrives with soil pH as high as 7.5. However, Stevia does not tolerate saline soils (Shock, 1982).
While a good compost usually satisfies nutrient requirements, soil testing or plant symptoms may alert you to deficiencies. Mark Langan of Mulberry Creek HerbFarm recommends low nitrogen or organic fertilizers. Excess nitrogen promotes rank growth with poor flavor. Bone meal, blood meal, cottonseed meal, guano, or dried manure provide nitrogen that is released slowly. Rock phosphate or bone meal provide phosphorous. Greensand is a good source of potassium. Rock phosphate, bone meal, and greensand offer a wide range of trace minerals. For maximum nutrient availability, work organic fertilizers into the soil a few months before planting, or mix with compost. For poor fertility soils, Blas Oddone (1997) of Guarani Botanicals, Inc. recommends incorporating 6 to 7 pounds of cattle manure per square yard. When using chemical fertilizers, a low nitrogen formula such as 6-24-24 is recommended in a split application - at planting time and again in mid summer. (Columbus, 1997). Steve Marsden of Herbal Advantage, Inc. simply uses a balanced vegetable fertilizer at the dose and intervals recommended on the container for vegetables.
Unless your soil is very sandy, raised beds are ideal for Stevia. A raised growing surface prevents standing water and reduces compaction. Beds should be 3 to 4 feet wide and 4 to 6 inches high. Till, disk, or spade the whole area thoroughly, then mark bed boundaries with string or garden hoses. Dig soil from the paths, 1 to 3 feet wide, and toss onto the beds until they reach the desired height. Beds may be left in place permanently. By walking only on paths, soil compaction is reduced. A mulch such as newspapers, grass clippings, or landscape fabric on paths will help control weeds. While not necessary, sides on the beds can be attractive and functional. Concrete blocks may be used, or rot resistant wood such as cedar, redwood, or locust. Raised bed "kits" made from plastic are available as well. Treated wood should be avoided because of possible soil contamination.