I have a very old Philadelphus and I know I was meant to cut it back after flowering in June but did not get round to it. It is full of old stems/branches and needs a good reviving, it also has ivy growing up through it. If I hack it back now am I doing more harm than good? Should I wait until next summer? It looks like it has needed this for several years, and hasn't flowered much for the last few years. Although I am posting from France the weather here is pretty much the same as southern England. Anyone got any ideas?