I know 2010 has just begun, but Amsonia hubrichtii (Threadleaf or Arkansas Amsonia) has been selected as the 2011 Perennial Plant of the Year.

I have not grown this plant in my own garden, although have seen it in others around here. I'm curious as to your experience regarding its true hardiness, as sources seem to state considerable variation. Some say to zone 4, others only to zone 6.

Thanks in advance.