Hi Polly. I find it doesn't seem to matter with the tall varieties. They take just about anything (clay, sandy, loamy and anything in between). It's the small varieties that don't seem to care much for the straight clay. Some even grow on the walls of my cement raised planters along the road out front. Tough little guys. I bet that make a really pretty picture, the iris with the tall sedum. Would love to have you put a picture in the Companion Plants Database if you can. Another idea of how to use sedum. If you have time here is a link. Would be lovely to see the iris.
http://cubits.org/sedumandsemp...
