Posted: 02/09/2016 at 07:33
It's not just the low temperatures, but also the low light levels, that slow plant growth down in the winter.
Cold frames are useful for over-wintering cuttings and seedlings to give them an early start in the spring, you could be picking Arctic King lettuce in early spring if you started them off in a cold frame now.
Commercial growers have large heated greenhouses and polytunnels, usually with lighting too.
If you want winter vegetables, there are some that you can grow in the open ground - Brussels sprouts, Savoy cabbage, winter cauliflowers (Aalsmeer are a good variety) but they need to have been started off back in late spring/early summer.
I've got Swiss chard growing in the veg patch now, which will carry on cropping through the winter with a bit of protection in the worst weather, and in late October I'll be direct sowing an overwintering variety of Broad Beans to get an early crop - usually picking in mid May.