The Cultivation of Stevia, "Nature's Sweetener"
The stevia plant (Stevia rebaudiana Bertoni), belongs to the Compositae (sunflower family of plants). Centuries ago, Natives of Paraguay used the leaves of this small, herbaceous, semi-bushy, perennial shrub to sweeten their bitter drinks. Originating in the South American wild, it could be found growing in semi-arid habitat ranging from grassland to scrub forest to mountain terrain. The plant made its way to Pacific Rim countries where in recent decades it became cultivated domestically, used in its raw leaf form and now is commercially processed into sweetener.
Similar soil and climatic conditions exist in Southern Ontario as that found where stevia originated. As a transplanted annual plant, stevia tends to grow well on a variety of soil types ranging from course textured sands to well drained loams but not clay or poorly drained sites. During the growing season, it seems to thrive in a temperature range of 15°C to 30°C provided all input resources and good management practices are incorporated. Stevia requires cultivation practices similar to those of other transplanted horticultural crops.
Stevia leaves have a long history of use as sweeteners, due to
the presence of sweet crystalline glycosides called steviosides
which are 200-300 times sweeter than sucrose. Stevioside is non-caloric,
non-fermentable, non-discolouring, heat stable at 95°C and has
a lengthy shelf life. The product can be added to cooked/baked goods
or processed foods and beverages. In the Pacific Rim countries,
China, Korea and Japan, stevia is regularly used in preparation
of food and pharmaceutical products.
Stevia is native to semi-humid, sub-tropical climates where temperatures typically range from -6°C to 43°C. While tolerant of mild frost, hard frosts will kill the roots of the plant. This lack of winter hardiness means that stevia can only be grown as an annual plant in Ontario.
Stevia grows well on infertile, acid soils, but can also be cultivated on more neutral soils (pH6.5-7.5). Stevia will not grow in saline soils.
Fields should be plowed and either disced and/or cultivated twice to prepare a fairly smooth, firm planting surface.
Transplants from cuttings would be superior, however the cost is prohibitive. Stevia must be propagated from seed in plug trays placed in a greenhouse for a period of 7 to 8 weeks.
In early to mid-May the stevia plug plants are planted into the field on either 53 cm or 61 cm row spacing with a total plant density in the order of 100,000 plants/ha.
The plant appears to have low nutrient requirements, however a soil test should be conducted. For the year 1995, test plots were fertilized with 100 kg/ha of 6-24-24 prior to planting and a split application of urea at 140 kg/ha
Normally, the stevia plant requires frequent, shallow irrigation. Generally, irrigation is required when the stem tips begin drooping.
Repeated mechanical row-cultivating can be used to control weeds. The crop may also require hand hoeing and weeding. Contact your local OMAFRA specialist to determine if any chemical control options are available.
Insect pest pressures other than cutworm are minimal. Septoria disease caused considerable damage to the over-mature 1995 crop. Contact your local OMAFRA specialist to determine if any chemical control options are available. Browsing by deer, who seem to like the sweet taste of stevia, may also be a problem.
Time of harvesting depends on variety and growing season. Generally harvesting occurs in mid to late September when plants are 40-60 cm in height. Shorter days induce flowering. Optimum yield (biomass), and stevioside quality and quantity are best just prior to flowering. The plant will tolerate temperatures to -6°C. Specialized harvesters may need to be fabricated to mechanize the harvesting process.
Drying of the woody stems and soft green leaf material is completed immediately after harvesting utilising a drying wagon or a kiln. Depending on weather conditions and density of loading, it generally takes 24 to 48 hours to dry stevia at 40°C to 50°C. An estimated 21,500 kg/ha of green weight is dried down to 6,000 kg/ha of dry weight.
Immediately following drying, a specially designed thresher/separator is necessary to separate dry stevia leaves from the stem. The yield of stem and leaf is similar at approximately 3,000 kg/ha each.
Dry leaves are stored in plastic lined cardboard boxes, sealed, strapped and labelled for further processing.
Economics of Production
Recent cost of production data for southern Ontario is not available, but research from 1995 indicates that sample leaf yields taken at the optimum harvest period have a yield potential of 2,850 kg/ha.
Stevia is commercially produced in temperate regions of the world where it can be grown as a perennial crop. For future Ontario growers to be competitive with these other production regions, development of winter hardy varieties of stevia is needed. Other requirements that are needed to reduce the cost of production include further refinements in agronomic practices, plant breeding to improve yield and quality, development of mechanisation techniques in transplanting, harvesting, drying and threshing, and the registration of pest control products.
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