Stevia, primarily from tropical and subtropical areas of South America, is a member of the Asteraceae family, making it a relative of chrysanthemum, sunflower, and many other plants with composite flowers. According to the Germplasm Resources Information Network (GRIN), there are 24 species of Stevia (other sources list up to 240 species). Of these species, only Stevia rebaudiana has the sweetening properties that make it useful as a sweetening agent. The substance responsible for its sweetening properties is stevioside. Commercially made extracts can be as much as 300 times sweeter than sugar.
Stevia in the Garden
Stevia rebaudiana is grown as a tender perennial or annual herb, depending upon where it is grown. Some references state that it is not frost-hardy and confine it to Zones 9-10. However, it has grown in my Zone 8B garden for several years. Admittedly, it gets killed to the ground during the winter, but it comes back reliably each spring. Even the past winter, which was colder than usual, had little effect. In areas where Stevia is not hardy, it can be grown as an annual.
I know that Stevia is an herb that is used to sweeten foods and beverages, and that its leaves are reportedly up to 30 times sweeter than sugar, but that is not why I grow it. As with many of my other herbs, it's just fun and easy to grow.
It seems to have within it properties that repel many insect pests that dine on other plants. Even pesky grasshoppers pass it by. Some leaf spots may be problematic, and they are best controlled by planting Stevia in a sunny location, limiting irrigation to very early hours so that maximum drying hours are maintained, and allowing for air circulation between plants.
Plant Stevia in well-drained beds in a sunny area, and maintain sufficient moisture by irrigating once or twice a week in the absence of rain. Mulch to inhibit weed growth and hold in moisture. Trim stems during the growing season to encourage bushiness. Low nitrogen or organic fertilizers are usually best, because excess nitrogen causes rapid growth resulting in leaves of reduced sweetness.
Expect Stevia to grow about two feet tall and wide. Welcome the beneficial insects that dine on the pollen and nectar produced by the small fragrant white flowers borne in clusters from the leaf axils.
Stevia roots easily from cuttings. Stick them in damp growing medium in small pots. When roots begin to grow out the bottom of the container, plants can be transplanted to the garden. Germination from seeds is highest when fresh seeds are used.
Benefits and Dangers
Needless to say, the non-caloric properties of Stevia hold attraction for those attempting to cut down their sugar intake. It can be useful to diabetics and to those who must manage their weight. It may also be useful in the treatment of high blood pressure and to those who must control their carbohydrate intake.
On the other hand, tests have concluded that stevioside affects the male reproductive system of rats. Female rats fed high doses had fewer and smaller offspring. Some studies have linked Stevia to the occurrence of cancer, but scientists admit that further testing is needed before a definitive statement can be made. Other studies indicate that stevioside can disrupt the conversion of food into energy by interfering with the ability of the body to absorb carbohydrates.
Since 2008, the Food and Drug Administration has declared that Stevia is "generally recognized as safe." However, cautions remain for pregnant women and those who are breast feeding. People who choose to use Stevia as a dietary supplement should check with their doctors to determine dosage and possible side effects.
Stevia leaves can be harvested directly off the plant and used as a sweetener in herbal teas and other drinks. Leaves have the greatest sweetening content just before plants flower, which is usually during the late fall.
Cut stems when plants are dry and hang them upside down in a warm, airy location. After they are dry, strip the leaves from the branches and store them in clean containers. Treated this way, they last for years. If you are lucky enough to have a food dehydrator, place them in it on low heat. Dried leaves will be bright green and crumbly.
Make Stevia powder by grinding the dried leaves in a blender or other appliance that will grind or chop the leaves finely. Use in recipes calling for green Stevia powder. Steep about one teaspoonful of dried leaves in a cup of boiling water and use it as a sweetener in herbal teas. One user reported that it makes the tea a bit thicker and smoother to swallow. Fresh leaves can also be steeped and used as a liquid sweetener.
Whether you grow Stevia for fun or for its sweetening properties, do include it in your garden. It is fun to have visitors break off a leaf and touch it to their tongue, and it is an attractive addition to the herb garden. You just never know. You may become a Stevia convert.