Hey Tomba
I too live in a 6a zone and just 2 years ago in the month of November we went from 70 degrees to 10 in less than 24 hours, needless to say this caused extensive damage to ALOT of trees and shrubs here. Not only did my boxwoods, spireas and Spanish brooms get dinged pretty hard but so did my knockouts which surprised me seeing as how iron tough they are, anywho, I'm still in the process of cutting out the dead ( off the top of my head I figure 30 plus of them ) but the first few were done that following spring and since what little I know about roses is most are scions on rootstock, I didn't want to cut too low. But I did notice that those I cut to near ground were just as healthy and robust as those I hadn't got to yet - even though the latter had noticeable dead branches - but by no means ' bushier' .
I will offer this advice though, get some tough leather gauntlets not gloves, those boys bite hard!, the kind that go to the elbows and NOT sold at big box hardware stores. My wife bought me a pair from Lowes that were too thin and tight. Lucky for me a wielder friend of mine gave me a pair that were too thin for HIS job!
Hope this helps.
J.R.
