I use plastic letter crates that you can buy at
office supply stores or Wal-Mart or Target
etc. I haven't noticed any problems for my
goldfish, minnows or plants.

Another great idea for a source, thanks!

You can also turn plastic nursery pots
upside down, but I don't find those as
stable (smaller "footprint" than the crates)
and have had some plants fall over.

Gail

Yeah, I tried turning a 4 gallon bucket upside down. It was okay, but
not too stable either, and it only held 1 plant.

Joan