Overwintering is summer planting for spring & summer harvest.
This is a different concept from winter gardening. Overwintered plants go into the cold season as "teenagers," waiting for the lengthening days of spring to finish growing. Certain varieties of onions, garlic, cauliflower and sprouting broccoli need this extra season to develop fully.
Typically, overwintered vegetables need to have some growth achieved before winter frosts—but they keep growing without being covered. In the early Spring, their growth rates speed up, and they are ready to be picked.
With some planning, overwintered crops can be combined with winter gardening and regular spring/summer gardening to provide fresh vegetables all 12 months of the year.
In our mild Coastal climate we can grow some vegetables all winter without protection. The greatest challenges are rain, low light levels and temperature swings. In harsher climates sheer cold becomes more significant. We recommend raised-bed planting to prevent waterlogging, which can kill winter plants. You can also protect your plants from harsh winds using a garden cloche.