Last fall, I left a couple spinach plants in the ground simply because I was lazy and didn't get them out before the freeze and snow. This spring, I noticed they sprouted and are growing! I hadn't realized that spinach can be overwintered -- even with single digit temperatures and no protection. The ground was frozen for months this year, and our snow cover was minimal -- but obviously enough the help the spinch live through the winter months. Mother Earth News claims spinach is one of the easiest plants to overwinter if you select the right varieties and let them grow to the right size before the ground freezes. They also claim mulching only rots the plants -- just let them out in the elements. That's what worked for me, by accident. I learned something new.