Gadenin日本語Get the appWarmth decides whether the seed comes up at all
Pepper seed is far fussier about temperature than most people expect. At 80 to 85F (27 to 29C) at the compost it comes up in seven to ten days. At 70F (21C) it takes three weeks and a good many seeds never make it. Below 60F (16C) germination is close to zero, which is why a tray on a cool windowsill so often produces nothing and gets blamed on old seed.
The heat needs to be at the compost, not in the room. A heat mat under the tray, the top of a fridge, or an airing cupboard all work. What does not work is a warm room with a cold draft over the tray.
| Compost temperature | Days to emerge | Proportion that come up |
|---|---|---|
| 85F (29C) | 6 to 8 | High |
| 80F (27C) | 8 to 10 | High |
| 70F (21C) | 14 to 21 | Patchy |
| 65F (18C) | 21 to 28 | Poor |
| Below 60F (16C) | Rarely | Close to none |
Move the tray off the heat the moment the first seedlings show. Bottom heat after germination is the fastest way to produce a tray of long, floppy stems.
Sowing
Nothing about sowing peppers is difficult once the warmth is arranged. Sow eight to ten weeks before your last frost, which is two to three weeks earlier than tomatoes.
- Sow at a quarter inch Cover the seed with a quarter inch (6 mm) of fine compost. Deeper than half an inch and weak seedlings exhaust themselves before reaching the light.
- Two or three seeds per cell Germination is not reliable enough to sow singly. Snip the weaker ones off at compost level once the true leaves appear rather than pulling them, which disturbs the one you keep.
- Cover to hold humidity A propagator lid or a clear bag keeps the surface from drying out over the ten days before emergence. Take it off as soon as the seedlings are up.
- Water from below Stand the tray in shallow water until the surface darkens, then lift it out. Watering over the top compacts the surface and pushes seed sideways.
Light straight away, or you get leggy plants
The moment a pepper seedling emerges it is competing with the light available. Too little and the stem stretches, the gap between the seed leaves and the first true leaves opens up, and you have a plant that will flop and never build a thick stem. This happens in the first week and cannot be undone afterwards, only worked around.
A windowsill is usually not enough early in the year. A cheap fluorescent or LED grow light two to four inches (5 to 10 cm) above the seedlings, running 14 to 16 hours a day, produces a completely different plant. Raise it as they grow to keep the same gap.
| Symptom | What it means | What to change |
|---|---|---|
| Long bare stem below the seed leaves | Too little light in the first week | More light, and move the lamp closer |
| Seedlings leaning steeply to one side | Light from one direction only | Turn the tray daily or add light |
| Pale, thin, stretching after a good start | Too warm at night for the light level | Cooler nights, around 65F (18C) |
| Purple tinge on stems and leaf undersides | Cold roots, phosphorus not taken up | Warmer conditions; it usually corrects itself |
| Growth stalled with yellow leaves | Hungry, or roots too cold and wet | Weak feed, and let the compost dry a little |
A gentle breeze from a fan for an hour or two a day, or brushing your hand over the tops once a day, thickens the stems noticeably. Movement is a real signal to the plant, not a gardening superstition.
Rescuing a leggy seedling
Unlike tomatoes, peppers do not root readily from a buried stem, so the standard advice to bury a leggy seedling up to its leaves is a good deal riskier here. It works, but only in warm, well drained compost, and a buried stem sitting in cold wet compost simply rots.
- Fix the light first There is no point rescuing a seedling into the conditions that stretched it. Get the lamp sorted before you do anything else, or it will stretch again.
- Pot up and bury moderately When you pot on, set the seedling half an inch to an inch (1 to 2.5 cm) deeper than it was, no more, into warm barely moist compost. That steadies it without inviting rot.
- Support with a splint A cocktail stick and a loose tie will hold a floppy stem upright while it thickens. It is less risky than burying and often all that is needed.
- Accept a late top if it is badly stretched A hopelessly leggy plant can be pinched out above the second pair of true leaves. You lose two weeks and gain a plant that branches low and stands up.
Potting up and feeding
Transplant into individual three inch (8 cm) pots once the first pair of true leaves is fully open, handling seedlings by a seed leaf and never by the stem. A crushed stem does not recover.
Seed-starting mix holds little food, so start a weak liquid feed at quarter to half strength about two weeks after transplanting seedlings and repeat every ten days. Do not push it. A fast, soft, overfed seedling transplants worse than a slower, harder one, and pepper plants remember a bad start for the whole season.
If a plant fills its pot and roots start circling before the weather is ready, pot up again into a five inch (13 cm) pot rather than planting out early. A rootbound seedling that sits for three weeks will crop late all season.
Hardening off, and what to write down
Peppers move from a warm, still, evenly lit indoors to wind, direct sun and cold nights, and doing that in one step scorches the leaves and checks the plant badly. Give it a full week to ten days: an hour of shelter and dappled shade on the first day, building to a full day outside, and only leaving them out overnight once nights are above 55F (13C).
Record the date you sowed, the date the first seedling emerged, the date you transplanted and the date you planted out, alongside how stocky the plants were. Pepper timing is the part of the season with the least room for error, and having last year's real dates in front of you is worth more than any general recommendation about weeks before frost.