This was my first winter trying to grow in a cold frame. It also happened to be the mildest winter I have spent in the New York City area, so it is hard to tell if the cold frame worked so well because it kept the garden bed warmer or because it was a mild winter. One thing is for sure in February I usually don’t have that much green lettuce and I have never had as many winter carrots as I did this year..
At a later date I will go over the custom design and construction of this cold frame maybe after I build another one and include some of the improvements I have thought of after a seasons worth of wear.
One thing I thought was useful was knowing the true difference in temperature between the cold frame and the outside air. In the photo below you can see a little white box on the far side that is a remote sensor to the wireless thermostat I have in the house there is another one right on the other side of the wood from that one. Generally what I noticed over the winter was that at night the air in the cold frame stayed 3-4 degrees warmer than the outside air, but during the day if there was any sun at all during the day the temperature in the cold frame would heat up to almost 70 deg even when it was 30-35 deg outside. This leads me to believe that durring the day the ground in this raised bed got much warmer and was able to retain that warmth through the night allowing a few deep freezes to pass by without affecting the plants inside.