Posted: 21/11/2014 at 10:52
It's not unusual to cut back tall growing roses by half to prevent wind rock over winter. If the weather is warm enough there can be some growth which wil probably be killed off by the cold of winter. New growth should appear again next spring. Once that happens you cut back to the new growth buds.
Clematis - well that's a minefield. Lyn is right you need to know what kind of clematis first of all. For the late flowered summer and autumn ones though, if you wait until the spring you can find growth all over last years whips and it feels somehow bad to be cutting off all those growing shoots, but of course if you don't cut back then you end up with a top heavy plant - bare at the bottom and all the flowers above you and out of sight! I have cut mine down to about three feet now, and will review and correct next spring.