Mustard and cress on a warm windowsill are the two winter crops that first spring to mind and some people limit their 'out of season' sowing to nothing more than this. The more adventurous will add micro-greens to the list but there are quite a few 'full-size' plants that will happily overwinter in a greenhouse or frame. I have two varieties of lettuce, carrots, chard, radishes and spring onions coming along nicely in the greenhouse.
Micro-greens are not just a handy and easy thing to grow in winter but they are a good way to use up old seed that you might not want to risk for the main sowings next year. They are simply immature plants harvested to be used as an addition to such things as salads, stir-fries, soups, casseroles, etc. Almost anything that has edible leaves can be used, including beetroot, broccoli, cabbage, celery, chard, kale, lettuce, rocket and more.
|for mustard and cress I use these pot trays with a little MPC in the bottom|
Today I've sown beetroot, CCA lettuce and kale in supermarket mushroom trays with a few drainage holes poked in the bottom. They'll be germinated indoors and put out into the greenhouse before they get too drawn in their search for light.
The beetroot are used for their leaves rather than letting them develop a root which would take too long anyway. As I go through my seed packet box and sort out what I no longer need I'll be sowing more over the next few weeks. All you have to lose is a little time. If seed doesn't germinate just use the compost for something else. How about peas sown close together and harvested for the shoots when they are a few inches high. When you think that micro-greens have become rather trendy in top restaurants and realize how easy they are to grow you need never associate home-grown and winter with boring.