This is my cold frame experiment from last fall. At that time I was ready to write it off as a failure, being that I had neglected to consider that maybe glass frames should be placed at an angle, to avoid excess pressure from ice and snow. You can see what happened.
On th brighter side, note the spinach plants, two of them, that survived a Minnesota winter under cover of plastic! So Eliot Coleman's four season gardening tactics might work here after all.