Hardening Off Seedlings: The Complete Walkthrough
This guide covers hardening off seedlings, rated an easy task, typically taking 7–10 days.
This is the expanded version of our hardening off seedlings guide, for anyone who wants the full detail rather than just the quick-reference card.
A 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.
Before You Start
Keep these points in mind:
- A sheltered outdoor spot (porch, cold frame, or similar)
- Seedlings ready to transplant
- A watering can for more frequent checks during the process
How It's Done
Worth paying attention to:
- 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.
When Things Go Wrong
Keep these points in mind:
- 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.
Timing and 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.
For the condensed printable version, head to the main guide page linked below.