I found a picture on Pinterest of a cold frame made of straw bales and old windows. This seemed like the best plan for me, as I have tons of hay bales for the llamas and several old windows from the barn. So a few weeks ago when we had a nice day I got to work.
The cold frame itself is very simple. Mine is 6 hay bales arranged in a rectangle, with 2 old windows on top. Originally I was using tiltable windows from the trailer we took down, but it turned out those were too much trouble (they would open on their own), so I switched them out for the simple wood frame ones from the top of the big barn. Luckily the new ones fit as well. I placed it on a south-facing slope (a gentle one though) so it would get the most sun.
|My cold frame.|
|Thermometer in the top left corner.|
|The old windows.|
The first day after I erected the cold frame, I checked the temperature when I was leaving for work (about 7:30 am). Unfortunately, it was only about 8*F higher than the air temperature- not nearly warm enough on nights when it is almost freezing!
|Temperature before windows were added (air temp).|
|Temperature just a few minutes after the windows were added.|
So I started researching ways to heat cold frames without electricity, and made some modifications. I added black landscape fabric to the sides and bottom of the cold frame, and put in a bucket of water. Both should absorb heat during the day and release it at night. Next week I'm also going to put a black trash bag in the bottom (for more heat), and some more landscape fabric on top (to shade the plants). I figure I can also fill the bucket with hot water from the house on really cold nights, which should help increase the temperature. It is supposed to get really cold again Monday night, but after that I'm going to try putting the onions and broccoli outside. I need to transplant more tomatoes, and I'm running out of room in the house!
If anyone has suggestions on better ways to design or heat a cold frame (without electricity), I'd love to hear them!