Jim M. I've grown them outdoors unprotected for maybe 8 years. They expand as a clump, but I have not seen them seed around. Even during our recent late freezes of 18 for two nights less than 2 weeks ago, the foliage has mostly popped back and some of them managed to bloom. Totally hardy here. Jim W. -- Dr. James W. Waddick 8871 NW Brostrom Rd. Kansas City Missouri 64152-2711 USA Ph. 816-746-1949 Zone 5 Record low -23F Summer 100F +