Stevia is the sweet-leaf herb: its leaves are intensely sweet and are used fresh, dried or powdered as a natural sweetener for tea, baking and drinks. In USDA Zone 8 it is grown as a tender annual, because although it is a perennial in warmer climates, Zone 8 winters — with lows of 10 to 20°F — are too cold for it to survive outdoors. That is no problem: Zone 8's long warm season, from March to November, gives stevia plenty of time to grow into a bushy, productive plant. This guide covers when to plant stevia zone 8, and what soil, spacing, sun, water and care it needs.
Zone 8 at a glance
Zone 8 has average winter lows of 10 to 20°F, an average last spring frost of Mar 1–15 and an average first autumn frost of Nov 15–Dec 1 — roughly 240–270 frost-free days in an average year. Frost dates are averages and ranges, not exact dates for any specific place: they vary by microclimate, elevation and year, so check your local extension service.
| Detail | Zone 8 guidance |
|---|---|
| Average last spring frost | Mar 1–15 (average/range) |
| Average first autumn frost | Nov 15–Dec 1 (average/range) |
| Days to germination | 7–14 days |
| Days to maturity | 90–120 days |
| Sowing | start indoors |
| Sun | full sun |
| Soil pH | 6.0–7.0 |
| Spacing | 18–24 inches |
| Water needs | moderate |
When to plant stevia in Zone 8
Start stevia seeds indoors 8–10 weeks before the average last frost — roughly late December to mid-January in Zone 8 — and transplant outdoors only after the last frost, from mid-March onwards, when night temperatures stay reliably above 50°F. Stevia is tender and a single frost will kill it, so do not rush it outside. Alternatively, buy nursery plants in spring and set them out after mid-March. With 90–120 days to maturity, plants started in January are ready for a first leaf harvest by late spring, and they keep producing until the first autumn frost in mid-November. The Zone 8 March guide shows what else is going out in the same window.
The planting calendar hub gives the Zone 8 picture month by month, and the frost date calculator turns your frost averages into sowing dates. Frost dates are zone averages, so keep row cover or a frost cloth ready from the day you plant, and check your local extension service for the dates that apply to your county.
Starting stevia in Zone 8
Stevia seed is slow and patchy to germinate — allow 7–14 days, and sow more seed than you need. Sow on the surface of fine seed compost, press the tiny seeds in lightly, and do not cover them: they need light to germinate. Keep the tray warm, around 70°F, and moist but not wet, under a bright light or on a sunny windowsill. Pot seedlings on once they have two sets of true leaves, and pinch the growing tips to encourage bushy growth. Harden plants off for a week to ten days before transplanting, putting them out for a few hours a day in a sheltered spot. The seed starting calculator helps you work out sowing dates from the average last frost.
Soil, spacing, sun and water
Give stevia full sun and light, well-drained soil — it hates wet feet, and heavy clay that stays soggy will rot its roots. It grows best at a pH of 6.0–7.0, in soil enriched with compost but not heavy fertiliser, which produces leafy growth with less sweetness. Raised beds and containers both suit stevia well in Zone 8, and a pot has the advantage that you can move it to shelter if a late frost threatens. Water moderately, keeping the soil evenly moist but never waterlogged, and mulch lightly to hold moisture through the hot summer.
Full sun is the light requirement, in soil with a pH of 6.0–7.0. Test your soil through your local extension service, and dig in well-rotted compost before planting. Space plants 18–24 inches apart — crowded plants stay small and invite disease, so use the plant spacing calculator if you are laying out a bed. Stevia needs moderate water: water deeply and less often rather than lightly every day. Check the soil a finger's depth down and water when it feels dry there.
Companion planting
Good companions for stevia include tomatoes, peppers, marigolds, cabbage. The companion planting finder can suggest combinations for your whole bed. Rotate crops each year and avoid planting where the same family (Asteraceae) grew last year, to reduce soil-borne disease. A related Zone 8 guide is catnip — another herb that thrives in Zone 8's long warm season.
Pests and problems
The common pests and problems to watch for with stevia are aphids, slugs, thrips. Aphids cluster on tender shoot tips in spring; wash them off with water or pinch out infested tips. Slugs may attack young transplants, and thrips can mark the leaves in hot, dry weather. Good air circulation and not overwatering prevent most problems, and stevia's sweet leaves are rarely bothered by larger pests. Inspect plants regularly, especially leaf undersides, and act early: hand-pick larger pests and wash aphids off with water. A pest guide can help you confirm what you are seeing before you treat it.
Harvest and storage
Harvest stevia leaves from late spring onwards, picking individual leaves or cutting whole stems just before the plant flowers — that is when the leaves are sweetest. Once the plant starts flowering, leaf sweetness drops, so pinch off flower buds as they appear to keep the plant leafy. Dry leaves in a warm, airy place out of direct sun, then crumble and store them in an airtight jar; dried leaves keep for a year. Use fresh leaves in tea, or grind dried leaves to a powder for baking. The plant will keep producing until the first frost in November, when you can cut the whole plant and dry the remaining leaves.
Frequently asked questions
When should I plant stevia in Zone 8?
Start seeds indoors in late December to mid-January, 8–10 weeks before the average last frost (Mar 1–15), and transplant out after mid-March when nights stay above 50°F.
Will stevia survive winter in Zone 8?
No, not outdoors — Zone 8 winter lows of 10 to 20°F will kill it. Grow it as an annual, or lift a potted plant indoors before the first frost in November and keep it in a bright spot.
When are stevia leaves sweetest?
Just before the plant flowers. Pinch off flower buds as they appear to keep leaves sweet, and harvest stems for drying at that stage.
Why is my stevia not germinating?
Stevia seed germinates slowly and unevenly, and needs light and warmth — sow on the surface, do not cover the seeds, and keep the tray near 70°F. Sow extra seed and be patient for 7–14 days.