You have nurtured your tomatoes and bedding plants on the windowsill for weeks, and the sun is finally out. Plant them straight into the garden now, though, and the shock can stop them dead. They need easing into the real world first.
Why it matters
A plant raised in the still, warm, even light of indoors is soft and unprepared for wind, cold nights and fierce direct sun. Thrown out without preparation, it can be checked so badly it takes weeks to recover, or simply collapses.
The gradual routine
Hardening off just means introducing the plants to outdoor conditions a little at a time over a week or two.
- Stand them out in a sheltered spot by day, bring them in at night.
- Leave them out a little longer each day.
- After a week or so, leave them out overnight if no frost threatens.
Use a cold frame if you have one
A cold frame makes the whole job easier: open the lid wider each day and close it at night, gradually leaving it open longer. No frame? A sheltered spot against a south-facing wall, with fleece thrown over on cold nights, does much the same.
Watch the weather
Keep half an eye on the forecast and never rush. A single unexpected late frost can undo all your careful weeks of growing in one night. Once the plants are properly toughened and the frosts have passed, they go out and barely notice the move.