I saw a quick glimpse of an idea on some show a couple of weeks ago that was a little interesting. They took a piece of roofing metal and folded it sort of in the shape of a rain gutter, then fashioned two ends with a piece of flat metal and screwed it together. Then they screwed it to a couple of post, it was about 6 feet long. My grandson works in a metal roofing fabrication place and I'm thinking about asking him what they would cost to make in their spare time. All kind of small plants could go in there, and you could hang 4 or 5 up on a wall or two post, it wouldn't take up much space and would be back friendly. You could make it as deep as you wanted it.

Sounds kind of like some of these hydroponic towers.

I thought the same thing. Had a friend who tried those and was very pleased with the results.