Last spring Walt built me a cold frame. You can read about it here and here. It provided a crop of early lettuce. In the fall I sowed half with more lettuce and half with spinach. We enjoyed a number of salad until the weather turned into a deep freeze. I pulled out the remaining lettuce and we ate one last salad. I kept in the spinach because the plants were small. They survived the winter but they did not grow. In fact the spinach looked like it was barely surviving. Now that we have very warm spring weather the spinach has taken off.