You can use so-called “season extenders” for winter gardening to retain some level of warmness for your plants and to protect them from wind and snow damage. This can be:
With this later system, you’re flexible when it comes to size. You can create small row covers just large enough to cover your plants; or you can create a kind of greenhouses, that you’re able to enter and work inside.
The benefits of these systems are, of course, that you use the greenhouse effect to heat up the air under the respective cover. As it will get cold at night nevertheless, best grow cold-resistant plants.
There are winter gardening vegetables that can be planted even in late fall or in the winter months (also when the ground is frozen). In fact, some plants (so-called cold season plants) are meant to be planted rather and will not grow as well if planted late in the year.
The benefit of planting early is that a.) You get healthy, resistant plants and b.) You get your vegetable yields much more early (in spring instead of in summer).
Before planting any seeds, you should always clear your beds of all dead plant material (also autumn foliage), crack the ground open, add compost and till it in. You can use organic fertilizers if your soil has been grown heavily during the preceding year.
You should not grow tubers and roots this early during the year, as they will easily rot from wetness. If, however, you combine the two tips I gave you in this article (cold covers & cold season plants), you can even grow potatoes before their time is due and transplant them into your “normal” beds once the weather gets warm again.