Gadenin日本語Get the appSurface sow, and never bury the seed
Torenia seed is dust. A packet looks almost empty, and a pinch tipped onto a dark surface reads as a smear rather than as individual seeds. Seed this small carries almost no food reserve, which is why it germinates in light and why it must sit on top of the compost. A seed pushed a quarter of an inch (6 mm) down will germinate and then exhaust itself before the shoot reaches daylight. If you feel you must cover it, use a dusting of sieved vermiculite thin enough that you can still see the seed through it, and no more.
Fill a tray with fine, sieved seed-starting mix, firm it flat, and water it thoroughly from below before the seed goes anywhere near it. Watering after sowing washes the seed into the corners and into the drainage holes. Once the surface is damp, tip the seed into the crease of a folded piece of paper and tap it out in slow passes across the tray, then press the whole surface gently with a flat board so every seed is in contact with wet compost.
Because the seed sits exposed on the surface, the top eighth of an inch (3 mm) of compost is the whole nursery, and that layer dries out in a single warm afternoon. One drying kills germinating seed outright, with no second chance. Cover the tray with a clear lid or a sheet of glass, stand it in a shallow tray of water when it needs topping up, and take the cover off the day the first seedlings show rather than a week later.
Temperature, and the timing that actually matters
Torenia is a tender warm-season plant with no frost tolerance at all, so the date that governs everything is your last frost, not the calendar. Aim to sow indoors eight to ten weeks before that date. That sounds long for a small bedding plant, but torenia is slow for its first month and a tray sown late produces plants that only start performing when the season is half over.
Germination wants 70 to 75F (21 to 24C) at the compost surface. In that range the first seedlings appear in 7 to 14 days and the tray comes up reasonably evenly. At 60F (16C) germination stretches to three or four weeks, comes up in patches, and the long damp wait is exactly the condition that causes damping off in seedlings this fine. A heat mat under the tray is worth more than any other piece of equipment here, and the tray should sit in bright light rather than on a dark shelf, because the light requirement does not end when the seed swells.
| Stage | Timing | Conditions to hit |
|---|---|---|
| Sow indoors | 8 to 10 weeks before the last frost | Surface sown, uncovered, 70 to 75F (21 to 24C) |
| Germination | 7 to 14 days at the right warmth | Surface constantly damp, bright light, lid on |
| Uncover | The day the first seedlings appear | Bright light, good air movement, no direct midday sun |
| Transplant | At the first pair of true leaves | One seedling per cell, handled by a seed leaf only |
| Pinch | At about 3 inches (8 cm) tall | Take out the growing tip above the second leaf pair |
| Harden off | Over 7 to 10 days before planting | Never below 50F (10C) overnight |
| Plant out | Two weeks after the last frost | Soil above 60F (16C), nights above 55F (13C) |
| Direct sow outdoors | Once soil holds above 65F (18C) | Raked fine, surface sown, shaded and kept damp |
From tipping the packet to a plant in the ground
The whole sequence is short but unforgiving in two places: the damp surface during germination, and the move out of the seed tray before the seedlings start to compete. Work through it in order and do not let the tray sit at the pricking-out stage for an extra week.
- Water the compost before you sow Stand the filled, firmed tray in an inch (2.5 cm) of water until the surface darkens, then let it drain. Sowing onto an already-wet surface is the only way to avoid washing dust-fine seed off the tray.
- Tap the seed out thinly and press it in Aim for far fewer seeds than feels right. A thick tray of torenia seedlings is nearly impossible to separate. Press the surface flat with a board so each seed touches wet compost, and do not cover.
- Give it warmth and light together Put the covered tray at 70 to 75F (21 to 24C) in the brightest position you have. Warmth in the dark gives you slow, patchy germination, because light is part of the trigger for seed this small.
- Uncover on the day seedlings appear A lid left on past emergence produces drawn, floppy seedlings that rot at the base within a week. Take it off, keep the compost damp from below, and give the tray gentle air movement.
- Transplant at the first true leaves Lift each seedling with the point of a dibber under its roots and hold it by a seed leaf, never the stem. One plant per small cell, set at the depth it was growing. Seedlings left crowded stall and never fully recover.
- Pinch the tip at 3 inches (8 cm) Take out the growing point above the second pair of leaves. This single pinch is the difference between one leggy stem and a plant that breaks into four or five branches and covers its space by midsummer.
- Harden off, then plant into warm ground Increase outdoor time over 7 to 10 days once nights are mild, and never leave plants out below 50F (10C). Plant two weeks after the last frost into soil above 60F (16C), and water in thoroughly.
Write down three dates every year: the day you sowed, the day the first seedling showed, and the day you planted out. After one season those numbers tell you exactly how many weeks your windowsill or greenhouse actually needs, and you can stop guessing at the packet's advice.
Direct sowing, and why most people should not
Torenia can be sown straight into the ground once the soil holds above 65F (18C), but seed this fine is badly matched to open ground. A single heavy shower buries it, a dry morning kills it, and slugs clear the first true leaves overnight. If you try it, rake the bed to a fine tilth, sow onto the damp surface, press it in with the back of a rake, and lay a sheet of row cover over the patch to hold moisture and keep the surface shaded until germination.
The other cost of direct sowing is time. Ground-sown torenia flowers four to six weeks later than plants raised indoors, which in a short summer means it starts just as the season is ending. Direct sowing makes sense in a long, warm season, or as a deliberate second flush sown alongside plants already growing, so that fresh young plants come into flower as the first batch tires.
Spacing decided now, not later
Torenia branches into a low mound roughly 8 to 12 inches (20 to 30 cm) across, and trailing forms spread wider. Set plants 8 inches (20 cm) apart for a solid carpet of color, or 10 to 12 inches (25 to 30 cm) apart if you want each plant to keep its own shape and to have air moving between them. Closer than 6 inches (15 cm) and the humid interior of the planting becomes a reliable home for gray mold in a wet spell.
In containers the rule is different and stricter: give roots real volume. A single plant needs at least a 6 inch (15 cm) pot, and three plants want a 10 to 12 inch (25 to 30 cm) bowl. Torenia has a fine, shallow root system with no reserves, and a small pot in summer heat dries at midday no matter how attentive you are. Decide the pot size at planting, because moving a flowering torenia in midsummer sets it back badly.