The yellow flags are out along the riverbank at the moment. They were planted in big native-planted reed bundles put down when the riverbank was rebuilt not to slip into the river any more, a slightly sad process which included the demise of some large trees. However, it's not all about size, and we never had so many Irises before. The reed bundles also contain beauties like native balsams and the ducks and moorhens seem to like the cover and dibbling opportunities, so thumbs up as a solid concrete bank softener.
Yellow flags are big, of course. Conceivably, I could grow a single clump of yellow flag in my water planters. But the rest of what's in them would probably have to go.