Re: Cold Frame Gardening
You are definitely not too far north for cold frame gardening. The sun is actually more of a limiting force on growing than the cold, so you are too late for winter crops (you need a longer day length for growth), but not for getting a head start on spring. A great resource for cold frame gardening is The Four Season Harvest by Elliot Coleman. The book includes planting and harvest times, which I feel is particularly helpful. Coleman is gardening in Maine, so it would be a similar zone to yours (I think zone 5).
The idea is to plant in fall when the day length is still long enough for growth and then use the cold frames to keep the crops alive and green so that harvest can take place throughout the winter. For early spring harvests, you can use the cold frames to get a jump on the season.