Well, upon doing a quick search, zone 6 is what I'm finding too, but I could have sworn I only ordered zone 5 hardy varieties that year I bought it from Chamblees. Mine are out in the exposed front yard, where they get lots of wind, and have been completely cane hardy. Makes me think with a touch of protection, Erfurt would do well for you.
'Ballerina' is a dependable performer in the garden. Some of the panicles of bloom are huge!
