These are not cold climate adapted and therefore always keep at it until finally shut down by the seasonal changes - damage to a last, ill-timed gasp of summer activity by the most recent shoot tips is to be expected and cannot be avoided. If you have chosen a locally suitable cultivar and put it in a warm, sunny, well-drained spot then survival of the planting as a whole should not be a problem. If recently planted and you are concerned about winter damage due to lack of full establishment mulch the roots well* to delay or even prevent deep freezing of the soil, retain what summer warmth is left longer than if the soil were bare.

*4 inches of wood chips or comparable material spread over an ideally several-foot-wide area but kept from piling against the stems at all times

This post was edited by bboy on Fri, Oct 17, 14 at 16:23