Hi Kathleen: Our experience at CBG strongly suggests that invasiveness is very much a regional characteristic. For instance in the Chicago area Buckthorn is invasive but in other regions experiencing a zone 5 climate it is not invasive. In other words, the ability to invade is based upon a complex interaction of environmental factors, not simply minimum winter temperatures. Boyce Tankersley Director of Living Plant Documentation Chicago Botanic Garden 1000 Lake Cook Road Glencoe, IL 60022 tel: 847-835-6841 fax: 847-835-1635 email: btankers@chicagobotanic.org "As a general guideline, if a particular species is a weed somewhere in the world, growing in the same hardiness zone you garden in, be very wary of introducing it to your garden."