I've tried hardening off with a day release in the garden but tbh I'm just going through the motions as I can't really see any difference! I don't have a cold frame but I tried a poly tunnel and things just end up bolting (presumably they're too warm for the amount of sun in spring).
I've been wondering about grow lights in any case, that's worth a try. Good point about the variety, I'd been using the same seeds and maybe they just weren't right.
Thanks for the suggestions.
