Stevia (Stevia rebaudiana) is a tender perennial herb native to South America, widely celebrated for its leaves which contain steviol glycosides, compounds up to 300 times sweeter than table sugar. This natural sweetener has become increasingly popular with home gardeners looking for a calorie-free sugar substitute. Saving seeds from this plant is a practical way to ensure a supply for the next growing season, especially for those treating it as an annual in cooler climates. Successfully collecting and storing these seeds requires careful attention to the plant’s reproductive cycle and post-harvest processing.
Recognizing Seed Maturity
Timing the harvest correctly is paramount for collecting viable Stevia seeds, as the small flowers do not all mature simultaneously. The plant must be allowed to bolt and flower, which typically happens late in the season, often corresponding to the shorter days of early autumn. The flowers are small, white, and tubular, growing in terminal clusters.
As the flowers finish blooming, the seed heads, called capitula, begin to dry and change color from white to a light brown or tan. A mature seed head displays a fluffy, parachute-like structure known as the pappus, similar to a tiny dandelion seed head. This pappus is attached to the actual seed, a slender achene about 3 millimeters long. Waiting until the stems and petals of the flower cluster are completely dry and slightly brittle ensures maximum maturity before collection.
Collecting Stevia Seeds
Once the seed heads have fully dried on the plant, collection must be done with care to prevent the seeds from dispersing. The achenes are easily carried away by air currents via the attached feathery pappus. Harvesting is best performed on a calm, dry day, ideally in the morning after any dew has evaporated.
A common collection method involves gently tapping or shaking the dried flower heads directly over a wide, shallow container or a piece of paper. Alternatively, the entire dried flower stalks can be clipped and placed upside down into a paper bag, which is then sealed and shaken vigorously. Due to uneven ripening, multiple harvests over several weeks may be necessary to maximize the yield of mature seeds.
Post-Harvest Cleaning and Drying
After collection, the raw material consists of a mixture of seeds, the feathery pappus, dried petals, and other plant debris, collectively called chaff. The process of separating the actual seed (achene) from this light material is known as winnowing. Viable seeds are small and dark brown or black, while non-viable seeds are often lighter, appearing tan or white.
Winnowing can be accomplished by pouring the mixture from one container to another outdoors on a slightly breezy day, allowing the lighter chaff to blow away. For smaller batches, gently blowing across the container’s surface will lift away the pappus and debris, leaving the heavier seeds behind. Isolating the dark, heavier seeds is important, as they have a much higher viability rate than the lighter, tan seeds.
The cleaned seeds must then be thoroughly dried before storage to prevent mold and spoilage. Spread the seeds thinly on a screen or a paper plate in a cool, dark, and well-ventilated area for one to two weeks. Direct sunlight or high heat should be avoided, as this negatively impacts future germination success. The seeds are fully dried when they cannot be easily dented with a fingernail and the remaining chaff feels brittle.
Understanding Stevia Seed Viability
Gardeners should set realistic expectations for Stevia seed saving, as the plant naturally exhibits a low germination rate, often falling between 10% and 40%. This low success rate is largely due to the plant’s breeding characteristics; Stevia is often self-incompatible and produces a high percentage of non-fertile seeds. The tan or pale seeds often found in a harvest are typically inviable achenes.
A more reliable method for propagating Stevia rebaudiana is through vegetative propagation using stem cuttings. Cuttings bypass the low fertility issue of the seeds, creating exact clones of the parent plant. For those determined to use seeds, proper storage is necessary for maintaining viability, which generally lasts for three to five years. Seeds should be kept in a small, airtight container, such as a glass jar, and stored in a consistently cool, dark, and dry location until planting.