Cold Frame Insulation

Over the last couple of days, Mother Nature has dropped an arctic cold wave over much of the county. Here in southwest Missouri, we have taken a pretty good hit also. On Sunday, December 14, 2008, the temperatures went from the high sixties to below freezing in just a couple of hours. Yowsers! Overnight, they then dropped into the teens. This is the first time in my memory that such cold came so early in the season. Hey! It’s not even winter yet! Outside, I have two small cold frames I built out of 2x4’s that house young and tender romaine lettuce plants along with a scattering of radishes and spinach. When I began the experiment in September, I had anticipated December temperatures dipping to the twenties once or twice, but not the teens like we have had for the last two days. That’s just too darn cold!

To their credit, the structures have insulated the plants pretty well so far. The temperatures tonight outside will be very cold again, dropping down to 18F or so. This level of cold has been a trial for the plants. I hope I’ve prepared for them by taking additional steps to insure their survival. On Sunday, I made sure to turn on the small 40 watt light sources I have installed in each frame and then covered them with spare floor mats. As a result, the internal temperatures in both cold frames have stayed in the mid to lower forty degree range.

In reflection, if I made any mistakes, it may be that I have neglected to build up the soil around the back side of each frame. The earth is a great insulator and the other three sides are covered well, just not the backsides. Next week, I plan to attach some additional insulation to see if that will help. Also, I’m hoping the ambient temperatures will moderate a bit during the rest of the month.