Gadenin日本語Get the appThe shape of the stevia year
Everything in the stevia calendar hangs off one fact: the plant flowers as the days shorten in late summer, and the leaf is sweetest just before those flowers open. Work backwards from that and the year makes sense. You want the largest possible bushy plant standing in the garden at the moment the buds form, and you want cuttings taken and rooted before you cut that plant down.
The second fact is that stevia is tender. It is a perennial in frost-free conditions, but in most gardens it is either grown as an annual or lifted and kept indoors over winter. That decision, made in autumn, sets what you do the following spring: an overwintered plant gives you a head start of a month or more over a fresh cutting.
Stage by stage through the season
The table below uses the season rather than dates, because the timing depends far more on your last frost and your day length than on any calendar. The two fixed points to watch for are the last frost, which governs planting out, and the appearance of flower buds, which governs the harvest.
| Stage | What to do | What decides the timing |
|---|---|---|
| Late winter | Take cuttings from an overwintered plant, or surface-sow seed on gentle heat | Needs 70 to 77F (21 to 25C); nothing roots or germinates in a cold room |
| Early spring | Pot rooted cuttings on, grow under cover, pinch at six inches (15 cm) | Light levels rising; growth accelerates noticeably |
| Mid spring | Harden off gradually over a week or two | Nights approaching 50F (10C) |
| Late spring | Plant out 12 to 18 inches (30 to 45 cm) apart in full sun, or pot into 10 inch (25 cm) containers | All frost past and nights reliably above 50F (10C) |
| Early summer | Pinch every shoot at eight inches (20 cm), mulch, water steadily | Plant growing hard; this is when the bush is built |
| Midsummer | Keep pinching, take cuttings from surplus tips, feed lightly if growth stalls | Longest days; the plant stays vegetative |
| Late summer | Watch for flower buds at the shoot tips, stop pinching, take your stock cuttings | Shortening day length triggers bud formation |
| Bud stage | Cut the whole plant to four to six inches (10 to 15 cm), strip and dry the leaf | Buds formed, no flowers open yet; the window is about a week |
| Autumn | Take a second smaller cut from regrowth, then lift or take cuttings for winter | First frost forecast |
| Winter | Keep the parent plant or rooted cuttings indoors, cool and barely watered | Short days; the plant is idle, so overwatering is the main risk |
Spring: getting a big plant, fast
The size of your harvest is decided in early summer, not at harvest time. A plant that goes out small and cold-checked in late spring will still be small when the days shorten, and it will bud up anyway, because bud formation depends on day length rather than on how big the plant is. So the aim in spring is a strong, well-branched, hardened-off plant ready to grow the moment the soil warms.
That means starting cuttings under cover in late winter, potting up promptly rather than letting them get root-bound, pinching once before they go out, and resisting the temptation to plant out early. Waiting an extra two weeks for warm nights costs nothing and often gains a month of growth.
- Start propagation on heat Take cuttings or sow seed in late winter with bottom heat at 75F (24C). This is the single most time-critical step of the year, because everything downstream depends on having a rooted plant ready in spring.
- Pot up before roots circle Move rooted cuttings into three and a half inch (9 cm) pots, then into larger pots if planting out is delayed. A root-bound stevia plant sulks for weeks after planting.
- Harden off over a week or two Increase outdoor exposure gradually before planting. Stevia moved straight from a warm windowsill into open ground scorches and stalls.
- Space generously Give plants 12 to 18 inches (30 to 45 cm) each way. Crowded plants shade each other, stay drawn, and hold humidity that encourages leaf spot.
Autumn: the decision that sets up next year
After the main harvest cut, you have a choice to make before the first frost. You can treat the plant as an annual and let it go, relying on new seed or bought plants next spring. You can lift it, pot it and keep it in a bright, cool, frost-free room over winter, watering only when the top inch (2.5 cm) of compost is dry. Or you can take a batch of cuttings, root them, and overwinter small plants that take almost no space.
The cuttings route is the most reliable and the least trouble. A large lifted plant is awkward, drops most of its leaves indoors, and is prone to rot from winter overwatering. Six small rooted cuttings on a windowsill survive far better and grow away faster in spring. Whichever route you take, do it before the frost, not after the first cold night.
An overwintered plant that survives will often run to flower earlier in its second year. Keep pinching it hard from early spring and treat any early bud formation as a signal to harvest that plant and rely on younger stock for the main crop.
The three dates worth writing down
Record three things every year and the calendar stops being guesswork. First, the date you planted out and the night temperatures around it, which tells you whether you moved too early. Second, the date you first saw flower buds, which is the fixed point the whole harvest hangs on and which barely shifts year to year. Third, the date of your first frost, which is the deadline for lifting or taking cuttings.
Add the weight of dried leaf you got from each plant and where each plant stood. After two seasons those few lines let you plan the whole year backwards from bud formation: when to take cuttings, when to plant out, and how many plants you actually need to keep yourself supplied.