In mid-November I planted lettuce, peas, onions, beets, and carrots. I got a good germination for all. In mid-December we got 13 inches of snow, which covered these young sprouts for three weeks. We had temperatures down to 19 degrees this winter, and freezing temperatures almost every night since the snow in December.
Only the peas and lettuce survived the cold and snow cover. The peas did the best, and are actually growing right now (end of January). Not all the lettuce survived, but some did. I suspect that had I planted in October, and these sprouts gotten better established, they would have done better. All should have survived the winter.
I know from past experience that lettuce, peas and carrots will winter over, under snow, in much colder temperatures than we have here. And established onions don't freeze. So it was the tenderness of these young sprouts that was the problem. I knew it was late to plant, but thought I'd try anyway.
I didn't plant any fall spinach, but my neighbor did, and says she has harvested it all winter, and it's the best spinach she's ever had. Fall and Winter is a great time to garden. Many gardeners ignore this time of year, but there are no pests, no diseases, and no weeds.