What's the best method for using water to store heat to be released
during the night to keep a cold frame from going below freezing?

I was thinking a bunch of those black balloons that you often see at
people's 40th birthday party - filled with water of course.

Any better ideas?

I got one of those Gro-quick heating cables, but it doesn't seem to be
doing much as far as heat production, maybe because it's only 15
degrees?

I have some plans for a great cold frame, not that it's rocket science
or anything. If anybody is interested it's just a PDF file - email me
and I'll send it to you.

Thanks,
Trace

Zone 5/Ohio