Greenhouse: New Cold Frame - 14' Wide by 26' long!, 1 by dreaves

dreaves wrote:
Clover or vetch either one should help.

You could improve the heat-holding capabilities quite a bit if you added a second layer of plastic inside the frame. I added 4-foot wide bubble wrap inside my frame and it does an excellent job of keeping the interior warmer. I posted a thread with tons of pictures of the whole process under "Shed Frame greenhouse".

Here's a photo of the bubble wrap inside.

David