Harden off half-hardy plants
May frosts still threaten, so our half-hardy plants won’t be planted out until early June. It’s crucial to harden them off first, for optimum ongoing growth. Wind is also their great enemy, as their delicate leaves are so far accustomed only to the calm warmth of a greenhouse. For us, hardening off takes up to three weeks. We put young plants into unheated cold frames with the lids down initially (and always at night), then open the frames slightly in the day. As the days progress, we open them for longer, until fully opened in the latter stages and slightly ajar on mild nights.