Cartwheel usually looks good when decorating, flowerbeds, flower beds. It is not necessary that it be any exceptionally old, unusual. This item is decorative in shape already., And for such an idea, as in the photo, any wheel will do.
The wheel should be fixed vertically by attaching it, for example, to a peg buried in the ground. Wire holders for containers with flowers are screwed to the top. You can make them more fundamental and weld to the rim, or you can just bend it from thick wire. The latter will provide an opportunity to put on a stand more or fewer flower containers, if necessary and desired.