Stevia Cultivation
Stevia grows best in sub-tropical climate. It needs rich garden soil, full sun and partly shade, humidity, high temperature, and plenty of water. Stevia Seeds are best sown in summer or in a warm greenhouse and should be lightly pressed into the soil but not covered with soil. The reason why it may not germinate if seeds are covered all over by soil. The stevia seeds need sunlight for the germination process. In Canada, it can be grown as an annual outdoors or year-round in a greenhouse. The ideal planting density is approximately 30,000 plants per acre with spacing of 30x60 cm in a raised bed system.
Soil Type
Stevia requires very good drainage. Any soil that retain the moisture for very long period of time are unsuitable for Stevia cultivation and should be religiously avoided. Similarly black cotton soils with very heavy clay content should also be avoided. It is mandatory that before planting, each and every soil sample should be properly tested and analyzed by an expert. Red soil and sandy loam with a 6-7 pH are best for the cultivation of Stevia.
In case of organic cultivation or poor soil texture like sandy soils, it is recommended to add compost to the soil. Five to seven tons of compost per acre per year will enhance soil texture and enrich soil with nutrients.
Land Preparation
Land should be ploughed initially with a disc plough or harrowed to break down the colds. Fine tilth is required. One to two times ploughing has to be done after harrowing.
Two main ways for plant arrangement in the field can be used:
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Raised beds with 25cm between the plants and 50cm between the rows.
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Stables 1m width with 3 plant rows (lines) on each stable and 25-30cm between the plants. If you are using plastic mulch, a flat field or stables may be used.
Raised bed preparation
Forming raised beds is the most economical way to grow Stevia. The raised bed should be of 15 cm in height and 60 cm in width. The distance between each plant 23 cm. This would give a plant population of around 30,000 per acre.
Planting
Stevia, a versatile plant known for its sweet leaves, can be cultivated in various methods tailored to the specific soil and climate characteristics of the region. The agronomic practices employed for Stevia cultivation play a crucial role in determining the success of the crop. To maximize yield, it is recommended to plant a minimum of 40,000 Stevia plants per acre. This high plant density ensures optimal utilization of space and resources, ultimately leading to a more productive harvest.
Planting Methods
There are basically three options for planting stevia. The first is the seeds, second the tissue culture and third the stem cutting.
​​Stevia propagation through seeds was once considered unrealistic due to poor seed germination and the lack of identical plants. However, with new varieties that have high germination rates and the experience gained in successful seed nurseries, seed propagation has become an important method of multiplying stevia populations. All stevia varieties in the market are open-poll, making seed propagation a viable option for growers.
​​Stevia can also be propagated through cuttings, with one plant producing up to 50 identical cuttings. However, stem cuttings require more facilities and experience, making it more expensive than seed propagation.
​​Tissue culture is a successful method for growing Stevia tissues in artificial media. It's the fastest way to multiply Stevia plants, and all produced plants are identical. However, cost is the main factor affecting the decision to use this method. Big labs offer better prices and a greater number of plantlets, but produced plantlets need acclimation in special greenhouses.
Plant Varieties
There are about 90 varieties of stevia rebaudiana developed all around the world. Basically all these varieties have been developed for different climate requirements, many times these varieties perform strangely in different climate conditions. In recent year, with new varieties that have seeds with high germination rates and since all stevia varieties in the market are open pollinated varieties along with better experience with successful seed nursery, seed propagation became an important method of multiplying stevia population.
At the end of the day, just like sugarcane, it is the stevioside and rebaudioside content in the Stevia leaves that determine the price and marketability of Stevia leaves. Nowadays, several varieties can have Reb-A content up to 80% of the total stevioside glycoside, with very little bitterness and aftertaste.
Irrigation
Stevia is highly dependent on the availability of water. Due to its shallow roots, the plant cannot access water deep in the soil. Therefore, the top 50 cm of soil should remain consistently moist throughout the growing season to ensure optimal leaf and sweetener production.
When relying solely on rainfall for stevia cultivation, the time between each rainfall should not exceed 3 weeks in clay soils. For sandy or semi-sandy soils, more frequent rainfall is necessary. If rain is delayed, additional irrigation becomes crucial.
If opting for irrigated cultivation with plastic mulch covering the soil, it is advisable to use drip irrigation.
Fertilizer application
The recommended fertilizer dose includes 4½ bags of urea, 2 bags of DAP, and 2 bags of Potash, with DAP applied at the start. Nitrogen and Potash can be split into 10 doses monthly. Nitrogen is crucial for dry matter production, but excessive use can lower sweetener concentration. Micronutrients are added only for plant deficiency symptoms. Both P and K fertilizers should be mixed well with the soil during land preparation.
Plant Protection
Stevia diseases often stem from high irrigation rates, humidity, or infected seeds. Infections can begin at planting and persist through plant growth stages. To prevent such infections, specific practices are crucial, especially when cultivating stevia in new pathogen-free locations.
Excess water in the root zone can reduce air and oxygen levels, promoting root rot disease. Additionally, too much water can hinder root transpiration, causing permanent wilting in plants. During heavy rainfall, it is crucial to drain excess water to prevent these issues.
The suitable plant population of 30-40 thousand plants per acre will avoid high humidity within the plant canopy.
Stevia plants are seldom affected by a large amount of harmful insects, suggesting that the components of the plant act as a natural insect repellent. Although there have been isolated reports of insect infestations, neem oil can be applied through spraying on the leaves in such instances.
Weed Control
Weeds pose a significant challenge to growing stevia. Without intervention, stevia plants struggle to outcompete weeds, particularly in the initial stages post-transplanting. Currently, there are no suggested herbicides suitable for controlling broad-leaf weeds in stevia cultivation.
Plastic mulch is an excellent weed control method suitable for annual cultivation (not advised for perennial cultivation). It prevents weeds from growing.
Another effective way to manage weeds is by utilizing cultivator machines. A well-chosen machine can be highly efficient in weed control.
Maintenance
Stevia plants thrive in a nutrient-rich, loamy soil similar to what common garden plants prefer. Given that their feeder roots are close to the surface, it is advisable to supplement sandy soil with compost for added nutrients. While sensitive to cold during growth, the roots can also suffer from excessive moisture. Therefore, it is important to avoid over-watering and ensure proper drainage in the soil to prevent it from becoming waterlogged or prone to flooding.
It is recommended to water Stevia plants lightly but frequently in the summer months. To prevent the shallow feeder roots from drying out, consider adding a layer of compost or your preferred mulch around each plant. Stevia plants thrive with fertilizers that have a lower nitrogen content compared to phosphoric acid or potash content. Using organic fertilizers that release nitrogen slowly is ideal. Avoid allowing the plant to flower, as Stevia has strong apical dominance, causing it to grow tall and thin. Pinching the apical bud will promote bushier growth with side branches.
Harvesting
Depending on climate conditions one can achieve the yields of 2000-4000 Kilos in three to six harvests annually. Another important aspect of harvesting is the timing of harvest. It should be noted that at no point of time plants should be allowed to flower since after flowering the Stevioside percentage goes down rapidly, and leaves are rendered unmarketable.
Leaves are harvested by plucking in a small quantity, or the entire plant with the side branches is cut leaving 10 to 15 cm from the base. The first harvesting can be done four to five months after planting. Subsequent harvesting can be done every three months, for three consecutive years. The sweetener in the leaf is maximum till the plant flowers.
Just before flowering, the plant should be cut completely leaving 10 cm from the ground. The new flush of leaves will sprout from here. The new plant will be ready for harvest again in three months. The plant yields around 3000 kg of dried leaves from an acre of plantation every year. Harvesting should be done as late as possible, since cool autumn temperatures and shorter days tend to intensify the sweetness of the plants as they evolve into a reproductive state.
Threshing
Separating the leaves from the stems can be carried out either prior to or following the drying process, depending on the type of machine being utilized. When using a combined machine, leaf separation occurs simultaneously with harvesting, which can be a time and cost-efficient approach. However, this method may not be ideal for cultivation spread across small remote areas. In such cases, it is a consideration whether to utilize harvesting and threshing machines (which may not be accessible) or to opt for machines solely designed for threshing (typically suited for dry leaves).
Drying Process
Once all leaves have been harvested it’s required to dry them. This can be accomplished on a net. The drying process is not one that requires excessive heat; more important is good air circulation. On a moderately warm fall day, stevia crop can be quick dried in the full sun in about 12 hours. (Drying times longer than that will lower the stevioside content of the final product.)
Crushing the dried leaves is the final step in releasing stevia’s sweetening power. The dried leaves are powdered, sieved and the fine powder is stored in containers. This can be done either by hand or, for greater effect, in a coffee grinder or in a special blender for herbs.
Packing
Stevia plants thrive in a nutrient-rich, loamy soil similar to what common garden plants prefer. Given that their feeder roots are close to the surface, it is advisable to supplement sandy soil with compost for added nutrients. While sensitive to cold during growth, the roots can also suffer from excessive moisture. Therefore, it is important to avoid over-watering and ensure proper drainage in the soil to prevent it from becoming waterlogged or prone to flooding.
It is recommended to water Stevia plants lightly but frequently in the summer months. To prevent the shallow feeder roots from drying out, consider adding a layer of compost or your preferred mulch around each plant. Stevia plants thrive with fertilizers that have a lower nitrogen content compared to phosphoric acid or potash content. Using organic fertilizers that release nitrogen slowly is ideal. Avoid allowing the plant to flower, as Stevia has strong apical dominance, causing it to grow tall and thin. Pinching the apical bud will promote bushier growth with side branches.
Storage
Stevia leaves can be stored for up to two years without any deterioration. A storage building must be 50cm above the ground with cement concrete to avoid flooding generated by rain. The ceiling and walls must be waterproof as well to protect leaves from rain. It is preferred that leaves are packed in well-sealed plastic bags to keep leaves from high relative humidity outside especially when the leaves are stored for long periods of time.
