Growing food
How to Harden Off Seedlings Before Planting Out
A step-by-step plan for moving indoor-raised seedlings outdoors gradually, with a simple day-by-day schedule and signs that plants are stressed.
Seedlings raised on a windowsill or under lights have soft growth. Sudden sun, wind, and cold can scorch or stunt them. Hardening off lets them toughen up gradually.
What you need
- A sheltered spot out of strong wind
- Somewhere shady for the first few days
- A tray or box so you can move pots in and out quickly
- Optional: a cold frame or horticultural fleece for cold nights
A sample schedule
Adjust to your weather – on a cold, windy, or very hot day, skip a step or repeat the previous one.
| Days | Outdoors | Position | Night |
|---|---|---|---|
| 1–2 | 1–2 hours | Shade, sheltered | Indoors |
| 3–4 | Half the day | Light shade | Indoors |
| 5–6 | Most of the day | Some morning sun | Indoors |
| 7–8 | All day | Full position they'll grow in | Indoors, or cold frame with lid closed |
| 9–10 | All day | Full position | Outdoors if nights are mild; cover if cold |
| 11+ | Plant out | — | — |
A cold frame makes this easier: open the lid a little more each day, then leave it open at night towards the end.
Signs of stress
- White or pale patches on leaves – sun scorch. Move back into shade for a day or two.
- Purple tints on leaves – often a sign of cold. Bring in earlier in the day.
- Wilting – check whether the pots are dry. Small pots outdoors dry out quickly, so check them every day (how to water container plants).
- Snapped or bruised stems – too much wind. Find a more sheltered spot.
Mild stress is normal and plants usually recover. Persistent damage means you are moving too fast.
When to plant out
- Check the typical last frost date for your area with your national weather service or a local gardening organisation, and keep watching the forecast – frost dates are averages, not guarantees.
- Plant out on a calm, overcast day or in the evening.
- Water seedlings in their pots an hour beforehand and again after planting.
- Keep fleece handy for the first couple of weeks in case of a cold snap.
Checklist
- Sheltered, shaded spot chosen for the first days
- Time outdoors increased gradually over about 1–2 weeks
- Plants brought in (or covered) at night until the end
- Pots checked for water daily
- Planted out after local frost risk has passed