It's possible to have fresh salad greens in the garden into winter (actually year round if you use a cold frame.) Garden chicories, endives and radicchio are some salad greens that will stand up through frost and under snow.
After a frost with weather predicted to be in the 20s, I cut the remainder of our chicory and endive, washed it, rolled it in a damp towel and stored it in the crisper. This gave us an extra week of fresh greens. Next year I plan to plant more so it will last longer.
Where we live it rarely gets below the 20s, so it is worth planting hardy vegetables. Carrots, beets, turnips will stay good in the ground as long as they are mulched on top to keep the roots from freezing.Takes a little planning, and energy for a bit of extra work after the main garden has been put to bed for the winter.