The temperature has finally risen above freezing, and I have just come in from uncovering the cold frame. I cover it with two-inch Styrofoam insulation board when the temperatures drop into the low thirties (F) at night. Our low was 20 F early this morning. Our frost date in this part of Wisconsin is May 21, so I’ll probably have a few more cold nights!
I waited for the sun to come around and shine on the cold frame before uncovering it. The temperature was a little above freezing inside the frame. A completely insulated box would be warmer, but I’ve had good luck with the insulation board so far. Once uncovered, the frame warms up quickly with even a little bit of solar. The types of plants I have in the frame withstand cold well: radishes, mesclun mix (cut-and-come-again greens), and spinach (which is all up now).
The bird bath is frozen solid, but it still is looking like spring in the cold frame! Growing green, Begonia