Mary, I've been pondering quite a bit on the matter of your soil freezing and needing the sun's rays to warm it up to thaw it.
Do you have any stones around? Stones, rock, brick, etc, are heat sinks for the sunshine. It seems to me that using rock as much as possible will provide you with a way to capture and store the sun's energy. It wouldn't make a gigantic difference, but every little bit helps. I bet the south facing side of a pretty good and heavy stone would be at least half a zone higher.
