That's a neat idea. I would probably need a lot of these because I own a lot of books. Great DIY idea for bookshelves.
I'm impressed. I wouldn't plant food plants in an old tire but why not decorative flowers?
DIY Concrete Garden Hands ** Says concrete but I would use hypertufa.
Turn your books into works of art using the Invisible Book Shelf - This is so awesome, I have so many books and I love them all, but storing them on a bookshelf doesn't show how great they are individually.