The Cultivation of Stevia, "Nature's Sweetener"

Table of Contents

1. Introduction
2. Introduction to Ontario, Canada
3. Agronomic Practices
4. Economics of Production

Introduction

The stevia plant 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. Similar cultivation practices to that of other transplanted horticultural crops are required for stevia.

From the leaves of stevia (S. rebaudiana), stevioside, sweet crystalline diterpene glycosides are extracted. Stevioside is non-caloric, however, measured to be 200-300 times sweeter than that of sucrose. Other attributes of this natural, high-intensity sweetener include non-fermentable, non-discolouring, maintains heat stability at 95 °C and features 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. In Japan alone, an estimated 50 tons of stevioside is used annually with sales valued in the order of $220 million Canadian.

The market opportunity appears great. Statistics indicate that in some countries up to 30% of their needed sugar is replaced by chemical-based (synthetic) stevioside-like sweetness products.

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Introduction to Ontario, Canada

The writer was first introduced to stevia at the request of a major Canadian food processor who had learned of the product and questioned whether or not the plant could be grown commercially and processed in Ontario. Through an acquaintance, who was visiting China, the first seeds plus cultivation practices printed in a Chinese language arrived in Ontario. In 1987 an attempt was made to grow stevia plants. Results were poor, attributed primarily to immature seed. In 1989 the crop was introduced to Dr. Cheng of the Agriculture Canada, Delhi Research Station. Dr. Cheng was on a work exchange in China and returned with an additional seed supply which was propagated and planted out during the 1989 and 1990 growing seasons. Since that time, several researchers based at the Agriculture and Agri-Food Canada, Pest Management Research Centre (Delhi) have been involved in plant breeding, plant pathology and agronomy.

A collaborative research agreement between Agriculture and Agri-Food Canada and Royal Sweet International Technologies Ltd. (RSIT) has been entered into. At the same time, RSIT of Vancouver, British Columbia in partnership with the Alberta Research Council, Edmonton, are developing new stevia processing technology which could result in a new natural, competitive sweetener. Research trials conducted at Delhi indicate attainable yields in the order of 2,000-3,000 kg/ha dry leaf and stevioside content ranging 15-20%, double that of other parts of the world where stevia has already been grown and processed commercially.

In the year 1995, six Southern Ontario farmers, located within the tobacco district, each planted one hectare of stevia on sandy soils. The six hectare experimental crop of stevia was grown under agreement with Royal Sweet International Technologies Ltd.

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Agronomic Practices

Land Preparation

The six experimental crop sites were plowed and either disced and/or cultivated twice to prepare a fairly smooth, firm planting surface.

Transplants

Transplants from cuttings would be superior, however cost makes it prohibitive. Stevia must be propagated from seed in plug trays placed in a greenhouse for a period of 7 to 8 weeks.

Planting

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 per hectare.

Fertilization

The plant appears to have low nutrient requirements, however a soil test should be conducted. For the year 1995, the recommended fertilizer program was 100 kg/ha of 6-24-24 prior at planting and 140 kg/ha of urea in a split application.

Irrigation

Normally, the stevia plant requires frequent, shallow irrigation. Generally, one applies irrigation if the stem tips are drooping. During the hot, dry 1995 growing season, irrigation was required at least one time per week. Generally, co-operators irrigated 5 to 10 times, some even more.

Weed Control

No herbicides are available for use. Agriculture and Agri-Food Canada is working on weed control research and application for minor use registration of certain broad-leaf weed and grass herbicides. In 1995, co-operators mechanically row-cultivated numerous times. The crop also required costly hand hoeing and weeding.

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Pests

Insect pest pressures other than cutworm are minimal. Septoria disease caused considerable damage to the over-mature 1995 crop. Deer seem to like the sweet taste of stevia, too.

Harvesting

Time of harvesting depends on land race variety and growing season. Generally it can be scheduled for mid to late September when plants are 40-60 centimetres in height. Shorter days induce flowering. Optimum yield (biomass) and stevioside quality and quantity is best just prior to flowering. The plant will tolerate temperatures to -6 °C. A specially designed and fabricated tractor mounted, one-row harvester cuts the plant at ground level and conveys it into a drying wagon.

Drying

Drying of the woody stems plus the 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.

Threshing

Immediately following drying, a specially designed thresher/separator is necessary to separate dry stevia leaves from the stevia stem. Stem and leaf portions tend to be equally represented at 3,000 kg/ha each.

Packaging

Dry leaves are stored in plastic lined cardboard boxes, sealed, strapped and labelled for further processing.

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Economics of Production

The cost of production for the first experimental crop averaged in the order of $8,500/ha. Sample leaf yields taken at optimum harvest period indicate potentially attainable yields of 2,850 kg/ha. Preliminary results indicate that in the order of 2,200 kg/ha of dried stevioside leaves are required to break even.

Agronomic practices require further fine tuning. Improved varieties through plant breeding and advances in pathology will, without doubt, improve yield and quality. Improved mechanisation techniques in transplanting, harvesting, drying and threshing, combined with registration of herbicides will reduce the cost of production. Stevia could potentially become a viable crop for Southern Ontario farmers.

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