I have a 2 and 1/2 foot square 'box' that is left over from an air conditioning project. It does not have a bottom on it. It does have insulating material glued to the inside. Pretty tempting to use as a planter on top of soil?

Would I need to paint it so the soil inside would stay cooler or would the metal reflect the sun and keep the soil cooler? There are the aesthetic considerations, of course, but first things first.

Maybe it would work well for faster compost?

Any ideas? Thanks!

Wobur