01A gradual transition

Seedlings raised indoors or under cover haven't experienced wind, direct sun, or temperature swings — hardening off toughens their tissue gradually so the move outside doesn't stall or kill them.

02What you'll need

A sheltered outdoor spot (porch, cold frame, or similar)
Seedlings ready to transplant
A watering can for more frequent checks during the process

03Method

1. Start 7–10 days before planting out.
2. Day 1–2: place outside in a sheltered, shaded spot for 2–3 hours, then bring in.
3. Day 3–5: increase to half a day, introducing a little direct sun.
4. Day 6–8: leave out most of the day, including some direct sun and light wind.
5. Day 9–10: leave out overnight if temperatures allow, then transplant.

04Troubleshooting

Wilting or scorched leaves — moved too fast into full sun; slow the process down.
Seedlings blown over — introduce wind exposure more gradually.
Forgot and left out overnight too early — a late frost can undo weeks of work; check forecasts carefully.
Seedlings dry out faster outside — check moisture daily during the process.

05Timing & maintenance

Best time

The 7–10 days immediately before your planned transplant date.

Duration

7–10 days for most vegetable seedlings.

Maintenance

Daily moving in and out, and moisture checks — the main effort of this technique.

Signs of success

Seedlings hold their form in wind and sun without wilting, and are ready to transplant without a growth check.

06Tips & variations

Pairs well with

Starting Seeds Indoors

Common mistakes

Skipping hardening off entirelyRushing the process in 2–3 days instead of a full week

Pro tip

A cold frame or unheated greenhouse makes hardening off far less labour — no carrying trays in and out twice a day.

Hardening Off Seedlings