Stevia rebaudiana, commonly known as sweetleaf or sugarleaf, is a plant native to the subtropical regions of South America, primarily Paraguay and Brazil. Indigenous cultures in these regions have used this herb for centuries to sweeten foods and beverages, often calling it “honey leaf”. These glycosides, particularly stevioside and rebaudioside A, are what give the plant its characteristic flavor, which can be hundreds of times sweeter than table sugar. Maximizing the concentration of these sweet compounds through proper timing and handling is the direct goal of any stevia harvest.
The Optimal Timing for Peak Sweetness
Timing the harvest of Stevia rebaudiana is directly related to the plant’s physiological stage and the ambient temperature. The concentration of these sweet compounds in the leaves is typically at its highest toward the end of the growing season. Gardeners generally look to harvest in late summer or early fall. Cooler temperatures in the autumn enhance the sweetness of the leaves, making this period the most opportune for a final, large harvest.
The single most important factor determining sweetness is harvesting before the plant begins to flower. Once the plant shifts its energy toward producing flowers and seeds, the quality and quantity of steviol glycosides in the leaves decrease significantly. Therefore, consistently trimming or harvesting the plant before flower buds fully form is an effective way to maintain high sweetness and encourage continuous leaf production throughout the season.
For the highest possible concentration of sweet compounds, the optimal time of day to harvest is in the morning. After the morning dew has fully dried, the leaves contain their peak levels of stevioside and other glycosides. Harvesting during the heat of the afternoon is less ideal because the plant may experience moisture loss, which can reduce the overall quality of the leaves. The plant itself should be mature, typically reaching a height of 18 to 24 inches, with bright green leaves.
Harvesting Techniques and Encouraging Regrowth
Stevia plants are resilient and can often be harvested multiple times within a single growing season, which is common in warmer climates. Using clean, sharp scissors or garden shears, the stems should be cut several inches from the base of the plant. It is important to leave approximately four to six inches of stem intact, especially making sure to leave several nodes or leaf sets on the remaining stub.
Leaving these lower nodes promotes the development of new lateral branches, which leads to a bushier, more productive plant habit. This practice of trimming encourages outward growth instead of upward growth, which translates directly into more leaves available for future use. When performing these intermediate harvests, it is generally advised not to remove more than one-third of the plant’s total foliage at any one time, allowing the plant sufficient leaf area for photosynthesis and rapid recovery.
Drying and Storage Methods
The steps immediately following the harvest are crucial for locking in the sweetness and preventing the loss of steviol glycosides. The leaves must be dried quickly to prevent browning, mold growth, and a loss of sweet compounds. An initial moisture content of around 80% in fresh leaves needs to be reduced to about 10% for long-term preservation. This quick reduction in moisture is achieved by air-drying the harvested stems or leaves in a cool, dark, and well-ventilated location.
Hanging the cut stems in small bundles upside down is an effective air-drying method that keeps the leaves away from direct sunlight. Direct sunlight and high heat can degrade the sweet compounds and lead to a loss of the vibrant green color. A food dehydrator offers a faster, more controlled environment, with temperatures set low, typically between 95°F and 120°F (35°C to 50°C), until the leaves are brittle and completely dry.
Once the leaves are fully dried and crispy, they can be easily stripped from the stems, which are often discarded due to their lower sweetness. The final step involves storing the dried leaves whole or lightly crushed in airtight containers, such as glass jars. These containers should be kept in a cool, dark place away from heat and light to maintain the potency and flavor of the stored stevia for up to a year.