Second layer of plastic and frost cover?

[bower]

Originally Posted by Cole_Robbie

Bower is cheating with all those water buckets!

LOL - just kidding. I do the same thing with horse troughs full of water, or at least am much as I can. I have never seen mass used under benches on a commercial scale. It might be difficult to do in a cost-effective manner. And it's the same with anything that costs more, it might work better on a smaller scale, but not translate well to a larger scale.

Too true about scale.
One thing I always noticed about the use of water containers as solar mass, it can take up one heck of a lot of space. I had these 5 gallon buckets anyway, and the plank was something I had laying around, so the usual "whatever you have handy" approach. But I think it makes a lot of sense for me to use buckets as the under-bench. Insofar as heat rises, any heat trapped or retained by the water is going to be released upward to the seedling bench.

BTW, I have learned it is a bit of a misnomer to think only about "solar" mass. The fact is, any kind of mass will act as a passive heat storage over time. Even mass which is not optimal (or optimally placed) for solar capture will absorb heat and come to temperature in a (solar or otherwise) heated space, which is then released slowly and moderates the temperature.