Stevia (Stevia rebaudiana) is a tender perennial herb (in USDA zones 9 – 11), otherwise usually grown as an annual. The leaves of the plant are a natural sweetener. Stevia is 300 times sweeter than sugar and is non-glycemic, calorie free and carbohydrate free. The USDA has approved its use as a dietary supplement. One plant yields approximately ½ pound of dried leaves. A little goes a long way. The leaves are sweetest just before the plant flowers in late summer to fall. Cooler temperatures and short days intensify the sweet flavor.
Growing the Herb Stevia
It is not recommended sowing Stevia seeds directly outdoors. Start inside 8 to 10 weeks before average last frost. Germination is best at 70 to 75 degrees F. Seedlings should emerge in 7 to 21 days. When seedlings are large enough to handle, you can transplant them into 3-inch diameter pots and keep inside until nighttime temperatures are above 50 degrees Fahrenheit consistently. Transplant outdoors in a prepared bed of rich well-draining soil incorporated with organic fertilizer and compost. Stevia prefers sun, but afternoon shade is ideal especially in hot climates. Space seedlings every 18 inches. Space rows 20 to 24 inches apart. Individual leaves can be picked at any stage or the whole plant pulled. Entire branches can be cut from a mature plant, and the leaves stripped off. Never remove more than 1/3 of the plant at a time if growth is to continue. To dry leaves, hang small bunches of stems tied together upside down in a dry, well ventilated room. When leaves have dried, remove and store whole. Crush before use.
In containers, hydroponics, or transplanted into the soil. Stevia can be grown year round indoors in containers with proper care. Pinch back to desired height.
Stevia can grow as tall as 4 feet (120cm).
Space Stevia plants 12 to 18 inches (30-45 cm) apart.
Preferred pH Range
Stevia will grow in a wide pH range between 5.0 (strongly acidic) and 8.0 (alkaline) with an ideal range between 6.5 and 7.5.
Stevia is most commonly propagated by seed indoors in flats or containers eight weeks prior to transplanting outside. Plant only very dark seeds when room temperature is between 70 and 75 degrees Fahrenheit for best germination results. Stevia is also easily propagated via cuttings and tissue culture.
Seed Germination Period
Stevia seeds will germinate in soil between approximately 7 and 21 days.
Number of Seeds per Gram
There are between approximately 2500 and 3000 stevia seeds per gram.
Stevia grows best in rich, well-drained soil incorporated with organic fertilizer and compost. Mulching helps keep roots cool and prevents moisture loss, while helping to deter weeds. Do not over water.
Alternative Growing Media
Soilless potting mixes (Pro-Mix, Sunshine Mix, etc.), perlite, vermiculite, rockwool, coco peat, Oasis Rootcubes.
Time From Seed to Saleable Plant
Seeds to finished plugs, 5 weeks; plugs to saleable plants, 4 weeks.
Sun & Lighting Requirements
Stevia grows well in full sun, with afternoon shade in hot climates.
Stevia will grow indoors satisfactorily under standard fluorescent lamps, and exceptionally well under high output T5 fluorescent plant lights, compact fluorescent, or high intensity discharge (metal halide or high pressure sodium) plant growing lights. Keep standard fluorescent lamps between 2 and 4 inches from the tops of the plants, high output and compact fluorescents approximately one foot above the plants, and HID lights between 2 and 4 feet above the plants, depending on wattage.
Have an oscillating fan gently stir seedlings for at least 2 hours per day to stimulate shorter, sturdier, and more natural plant habit.
Zones 9-11 as perennial; annual in all other zones.
Requires consistently moist soil during summer heat. Water stevia on a regular schedule, allowing soil to go almost dry. Guard against overwatering, especially in containers and after transplanting.
Potential Plant Pests and Diseases
Pest and diseases are not generally a problem with stevia. Besides cutworm and animals that like the sweet taste, pests are minimal. Aphids, thrips and whiteflies can be a potential problem in greenhouses.
It is best to harvest stevia plants just prior to flowering, as the flowers can impart an unpleasant flavor to the leaves.