The short answer
Acclimatise indoor-raised plants gradually before leaving them outside. Hardening off does not make a frost-sensitive plant frost-hardy.
See the sourceIn this guide
Check your situation
- Check current and forecast conditions where plants will stand.
- Consider how protected they have been and how tender the crop is.
What to do now
Begin in shade and shelter
Begin with a few hours outdoors in a sheltered, shaded place during mild daytime weather.
Protect tender plants at night
Bring tender plants under protection at night initially.
Increase exposure gradually
Increase exposure gradually as plants and conditions allow.
Diagrams explain the text; they are not to scale.
Protect tender plants whenever frost threatens.
What not to do
- Do not move directly from a protected setup into exposed conditions.
- Do not treat hardening off as protection against frost.
Do you need to buy anything?
A sheltered spot may suffice. A cold frame can provide an intermediate stage, but is not required for every grower.
Keep going
Sources behind this page
- RHS: Hardening off tender plantsUnited Kingdom. Acclimatising protected plants. Timing depends on the crop and weather.Source checked 7 October 2026
- University of Minnesota Extension: Starting seeds indoorsMinnesota, United States. Indoor seed starting. Regional calendar dates are not universal.Source checked 7 October 2026
We summarise published guidance. We have not independently tested these methods or the products discussed.
AI-assisted editorial check: 7 October 2026. This is a source and clarity check, not a review by a horticultural expert.