Growing Your Own Stevia
By Jeffrey Goettemoeller
Stevia rebaudiana is a fascinating plant, native to the higher altitudes of Paraguay and Brazil in South America. Stevia is the genus, meaning a broad classification of plants. Rebaudiana is the species name. Only this species, out of the many found in the Americas, contains the high concentration of sweet glycosides making this “sweet leaf” such a useful and amazing herb. The dried leaf, in fact, is 10-15 times sweeter than cane sugar! Powdered stevia leaf, known as green stevia powder, may be found for sale at natural food stores or online while waiting for your first harvest.
Not a particularly showy plant, stevia’s sweet taste is its most notable feature. It is a non-woody herb with somewhat stiff and brittle stems. Stevia leaves are small and narrow, notched on the end. The leaves are much sweeter than stems. Plants reach about 2 feet in height. Stevia blossoms are white and tiny, but so numerous that blooming plants look like greenish-white clouds. Stevia is a tender perennial herb, which means it survives winters and keeps growing, but only where winters are mild. The roots may survive some winters as far north as USDA hardiness zone 8.
Fortunately, stevia may be grown as an annual outdoors. The long summer days in colder climates are actually an advantage for growing stevia. Plants grown at higher latitudes with more daylight will have more leaves and a higher percentage of sweet glycosides.
Soil and Culture
Stevia will grow well on most soils, but prefers a sandy loam or loam, high in organic matter. Its native soils are on the acid side, but stevia tolerates a wide range of soil pH. Stevia likes consistently moist soil, but not waterlogged. Standing water can cause plant rot. Except in the case of very sandy soils, raised growing beds provide Ideal conditions.
Growing beds are made by mounding soil 4-6 inches high and 3-4 feet wide with a level top surface. Dig soil from the paths if it is fertile. Otherwise, think about adding compost, peat moss, or other organic soil amendments.
Watering is essential unless substantial rains come every week. Soaker hoses such as the “weeping” hoses made from recycled rubber are ideal for supplying moisture consistently. Mulch is optional, but advisable, especially if a soaker hose is not used.
Light is important for stevia as well. Day length is more critical than light intensity. If your summers are extremely hot and sunny, afternoon shade will be beneficial. The long days of spring and early summer favor leaf growth. The short days of late fall will cause stevia plants to blossom.
Getting Started
Stevia may be grown from seeds or plants. Visit www.steviaseed.com or request a retail list by mail to order quality stevia seeds from yours truly. Stevia seeds should be started inside under plant lights or fluorescent lights several weeks before transplanting outdoors. See my article on seed starting for more details. Stevia is sensitive to cold temperatures, so set the plants out at least 2 weeks after your usual last frost date. Harden plants for 4-6 days before transplanting by placing outdoors in a protected area. Bring indoors on cold nights. Try to transplant on a cloudy day or in the evening. Use a trowel to set the plants a little deeper than they were in the pot. In a 3-foot wide bed, use two staggered rows so that plants are not directly across from one another. Space plants 12-18 inches apart in the row. Gently firm the soil around the plant with your hands. Avoid walking or kneeling on the bed itself so the soil stays loose. Water the plants well with a gentle soaking right after transplanting. A little mulch around new plants will prevent rapid drying on sunny days.
Stevia stems are brittle and tend to break in the wind. Pruning plant tips to promote branching will help, and should be done anyway for maximum leaf yield. When the main shoots are eight to twelve inches long, simply pinch or cut off growing tips. Branches will sprout where the leaves join the stem, creating a bushy plant less prone to breakage. When side branches reach seven to ten inches, go ahead and pinch leaf tips again. Pruned leaves taste good eaten on the spot. Alternatively, tip leaves may be dried or used fresh for herb tea.
Plants may be dug up and brought indoors for the winter with the use of a fluorescent shop light or grow light kept on 14-16 hours per day (a timer may be used). They will need pots large enough to comfortably hold all the roots. Indoor plants can produce useable amounts of stevia and support stock plants for taking winter cuttings. The plants tend to look half dead by the end of winter, but they usually sprout back nicely in the spring.
Propagation
Stem cuttings root easily in late winter or early spring if two key conditions are met. First, at least 14 hours of fluorescent light per day will encourage quick rooting. Secondly, horticultural grade vermiculite or perlite seem to be the best rooting mediums. Use small pots or cell packs with holes in the bottom and water from below as needed to maintain a constantly moist medium. Cuttings should be 2-4 inches long with at least two leaf buds above ground. Remove all but 2-3 small leaves. After 2-4 weeks, transplant to a larger pot with a light soil mix and allow wait another 2-4 weeks before transplanting outdoors.
Harvesting
Stevia leaves may be harvested through the summer as needed. For the highest yield, harvest just as the first blossoms open in the fall. Cut whole stems, leaving 1/3 of the stem length if you want to let the plant re-grow. Strip the leaves and discard the stems. Leaves may be used fresh for making tea or eaten right off the plant as a sweet treat. They taste great with mint leaves. Leaves may be dried for later use by spreading out in a warm spot with good air circulation or in a food dehydrator on low heat. Store the leaves in an airtight container such as a glass canning jar. The dried leaves remain sweet for many years and may be ground into a powder with a kitchen blender, food processor, or mortar and pestle. Now all that’s left is enjoying your sweet harvest!
Find more about growing stevia in Jeffrey's book, Growing and Using Stevia: The Sweet Leaf from Garden to Table with 35 Recipes.