Stevia

Dried stevia leaf goes for $15-25 per pound at health food stores and herb markets (USDA AMS Specialty Crop Market News, 2023). The active compounds - steviol glycosides, primarily stevioside and rebaudioside A - are 200-300 times sweeter than sucrose by weight (USDA Agricultural Research Service, Steviol Glycoside Content in Stevia, 2018). One small plant yields enough dried leaf to sweeten hundreds of cups of tea. If you use caloric sweeteners and would prefer not to, this is the most direct substitution available from a home garden.

What it actually is

Stevia is a semi-woody perennial shrub native to Paraguay and Brazil, in the Asteraceae family (same family as chamomile, calendula, and sunflowers). The species used commercially and in home gardens is Stevia rebaudiana. Plants grow 18-24 inches tall, with small, oval, serrated leaves and tiny white flowers when they bolt.

The sweetness comes from the leaf, not the flower. The glycoside concentration is highest just before flowering. Once plants begin to flower, glycoside content drops and plants put energy into seed production rather than leaf growth.

Stevia is a tender perennial - it survives outdoors year-round only in zones 9-11 (where frost is rare to absent). In zones 8, it may survive mild winters with heavy mulching. In zones 4-7, it dies with hard frost and should be overwintered indoors as a potted plant or propagated from cuttings before frost. It regrows vigorously from the root crown if protected from freezing.

The ROI case

A packet of stevia seed costs $3.99. Here’s the practical issue with seed: stevia seed germination is notoriously inconsistent, with rates as low as 20-30% even from fresh seed (Cornell Cooperative Extension, Stevia Production Guide, 2019). Buy transplants or propagate from cuttings for reliable establishment - most garden centers carry starts in spring. One established plant produces 0.25-0.5 lb of dried leaf per season, worth $3.75-12.50 at market rates. That’s a modest return by dollar value, but the functional return - in replacing $8-12/lb of processed stevia powder or $0.50-1.00 per bag of stevia packets - is more meaningful.

If you keep the plant alive for multiple seasons (zones 8+ or with indoor overwintering), seed cost disappears from the calculation entirely. A 3-year-old stevia plant is a significantly larger, more productive shrub than a first-year transplant.

Growing requirements

Start seeds indoors 8-10 weeks before your last frost date, pressing them onto the surface of a well-drained seed-starting mix - stevia seeds are tiny and need light for germination. Keep soil moist but not wet at 70-75°F. Given the low germination rates, sow at least 3-4x as many seeds as you need plants. Alternatively, purchase starts.

Transplant after all frost risk has passed and soil temperature is above 65°F. Stevia is cold-sensitive; a late frost will kill transplants that have hardened off insufficiently.

Soil pH of 6.5-7.0. Well-drained, moderately fertile soil - stevia is susceptible to root rot in wet soils. Raised beds or mounded rows improve drainage. Do not over-fertilize; high nitrogen pushes vegetative growth but dilutes glycoside concentration in the leaves.

Full sun (6-8 hours) is non-negotiable for good glycoside development. Shade-grown stevia produces significantly lower sweetener content.

Space plants 18-24 inches apart. Pinch growing tips at 8 inches tall to promote branching and higher total leaf yield.

What goes wrong

Root rot is the most common failure, almost always caused by poorly drained soil or overwatering. Stevia’s roots are shallow and intolerant of saturated conditions. Plant in raised beds or well-amended, fast-draining soil. Water 1 inch per week and let the top inch of soil dry between waterings.

Low germination from seed is an expected issue - not a failure. Commercial stevia seed has low viability even when packaged correctly. Plan for it by sowing heavily, or skip seed entirely and buy starts.

Aphid infestations on new growth are common, particularly indoors on overwintered plants. Treat with insecticidal soap at first sign. Aphids on outdoor plants are usually managed by natural predators once the season is underway.

Bolting triggered by long daylength (above 12-14 hours) reduces leaf quality. Pinch flowering stems before they fully develop. In northern gardens (zone 6 and above), bolting typically occurs in August.

Harvest and storage

Harvest just before the plant flowers - this is when stevioside content is highest. Cut stems back by two-thirds, leaving the lower foliage to regrow. Strip leaves from stems and dry in a single layer at room temperature (75-85°F) for 3-5 days, or in a dehydrator at 95-105°F for 1-2 hours. Properly dried leaves crumble easily.

Store dried leaves whole in glass jars away from light. They can be used directly in tea (1-2 leaves per cup) or ground to a powder in a spice grinder or mortar. Dried stevia loses potency slowly - properly stored leaves remain effective for 2-3 years.

To overwinter: dig the plant before hard frost, cut back by half, pot in a container, and bring indoors to a south-facing window or under grow lights. Water sparingly through winter. Return outdoors after last frost.

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Related crops: Basil, Mint, Chamomile

Related reading: Seed Saving Guide - why saving stevia cuttings beats saving seed, and how propagation by division works