Jennifer Schultz Nelson
Extension Educator, Horticulture
Tired of the same old herbs in your garden each year? Looking for something different? Consider stevia, an ancient herb that is gaining popularity in the U.S. The common name for stevia is sweetleaf or sugarleaf, hinting at what this herb has been traditionally used for by many cultures.
Stevia is a small shrub-like plant native to South and Central America. For centuries, the Guarani Indians of Paraguay have used stevia as a sweetener for maté tea, a traditional beverage. In Japan, stevia accounts for about 40% of the sweetener market, and many ready-to-eat products are sweetened with stevia. Many products familiar to Americans like soft drinks and chewing gum are sweetened with stevia in Japan.
The sweetness of stevia is due to molecules called glycosides produced in the leaves. A general definition of glycoside is any molecule which has one or more sugar molecules attached to it. The human body recognizes the sugar portion of the glycoside as sweet, but cannot break apart the glycoside to use for energy. In effect, this makes the glycoside have no calories. The glycoside stevioside accounts for most of the glycosides in stevia, and some report it to be as much as 300 times sweeter than sugar. One estimate says that one leaf is roughly equivalent to two teaspoons of sugar in sweetness, and two tablespoons of ground dried leaves can be as sweet as one cup of sugar..
Despite wide usage as a sweetener by world cultures, in 1991 the U.S. Food and Drug Administration (FDA) banned the use of stevia in food products, calling it an "unsafe food additive". Their position mellowed somewhat by 1995, when they decided to allow the sale of stevia only when labeled as a nutritional supplement, not as a sweetener.
The FDA's conservative stance on stevia is due to a few animal studies that have indicated potential health problems linked to stevia, particularly cancer. The number of studies indicating possible health risks are few, but there are not enough studies indicating stevia's safety for the FDA to allow it to be considered a safe food ingredient or to be sold specifically labeled as a sweetener.
Stevia has foliage which consists of somewhat small, elliptical, hairy leaves. The flowers are borne in clusters of two to six florets. Typically plants are about two feet tall and wide, but may reach three feet or more in height and width when grown in rich soil.
Plants are tolerant of a wide range of growing conditions, as long as there is adequate drainage. Stevia prefers full sun, but can tolerate partial shade. The long days and heat of summer favor increased numbers of leaves as well as higher yields of steviosides.
Propagation of stevia is most successful via cuttings and layering. Stevia seeds have particularly low germination rates (10% or less) because they are self incompatible. That is, pollen from a plant will not produce a viable seed if it pollinates a flower on the same plant. There may be a structure that resembles a seed, but it is sterile.
Stevia may be grown as a perennial in USDA hardiness zones 8 and above. This means in central Illinois, which is zone 5, it is grown as an annual. It can be successfully grown in containers and overwintered indoors.
Stevia is sold commercially as a nutritional supplement in several forms, including liquid extracts, powders, and fresh or dried leaves. Sweetness of products may vary considerably, as there is currently no regulation on the amount of steviosides that extracts contain.
No matter what your reason for growing stevia, it is a unique addition to your herb garden. It is also a great example of people finding a practical use for compounds manufactured by plants, nature's best chemical factories.