Freeze proof containers?
I live in RI, zone 6b, so any containers that I want to leave out all winter (with soil in them) need to be completely freeze proof. This is not the same as "frost proof" since those usually only mean that a little frost on an empty pot won't damage it. I have one stone container with a small pine tree in it that's been fine for years, but I need something bigger that I won't have to move at all. I'd plant annuals every year, but I need large scale containers that can stay put. The size would be in the range of 24-36 inches high, at least and probably 24-30 inches in diameter. I have another pot that resembles stone, but it's made of some sort of plastic, resin or fiberglass type material. It's also lasted for many years, with soil left in it all year. It really looks almost like real stone, but I haven't been able to find any more like it, and not sure what it's made of. Any suggestions are welcome!