In our climate, cold frames are useful, but not as much as they are in places with milder climates. If they are in the sun, you cannot leave plants in them in winter, because temperatures in the frames can fluctuate enormously. They stay buried in ice and snow for most of the winter. However they are especially handy in spring.
I use mine to start seeds in the spring or to protect plants from a late cold snap. One less conventional way I use them is to warm up water. I have watering cans filled with water which I leave in the cold frames, and after several hours of sunshine the water gets tepid which is appreciated by plants like tomatoes.
However the heat that warms up the water also causes problems. I have often mentioned that there are few humans around here, but lots of wild life. At this time of the year, on sunny days, snakes get into the cold frame to bask in the sun. These are garter snakes or milk snakes which are not dangerous in any way (actually milk snakes are better mousers than cats, and I always treat these with due respect - I am not so fond of garter snakes as they eat our frogs in the rill).
|Garter snake visiting the cold frame on a sunny day|
All this to say that I am always nervous lifting the light of a cold frame and especially getting a flat of plants out of the frame, because if there is a snake, it will usually be having a little snooze curled up under a flat of plants. I am not afraid of them but they always make me jump. Once the snake sees you, it tries to get away, but, strangely enough, usually it does not seem to remember where it came in as it scurries around trying for find a way out. The garter snake in the pictures above and below, which visited the cold frame this morning, was trying to squeeze itself into a hole in the stone wall that backs the cold frame. However it did not fit in the hole completely, the tail remained sticking out. When I checked a few hours later it was gone.
To end the post with some colour - the last tulips of the season.