I think most marginals could be grown in that, but stick with dwarf and small plants. I've grown acorus, small water iris, lobelia cardinalis, dwarf papyrus, and other things in containers such as this. I find that in anything less than 3 feet across I end up thinning and replanting every year to keep growth in check, though. 12 inches is small enough to easily be consumed by single plant unless managed.
