Anita, in my zone 7a garden I prune all my clematis in late December. Fall is generally not a good time to prune since the clematis will more than likely still be actively growing and pruning will stimulate more growth. This is not what you want to happen when colder weather is set to arrive. As to your second question, some of the cut vines may fall off in the winter wind but some may stay and require removal by you. It all really depends how much you are planning to cut off, how much you leave on the plants, and how windy and turbulent your winter weather is.

While it is not exactly a "rule", it is generally considered to be a very sound practice. The hard pruning of any newly planted clematis encourages the development of a good root system. And with pruning group 2 clems - those most prone to clematis wilt - a well-developed root system can go along way to discouraging this issue. I would recommend cutting your new clems back hard in late winter. I might even consider stretching that out to the following season as well. At best it will only delay the initial bloom flush a few weeks. I know sometimes it's hard to imagine that far ahead when your vine looks good right now but truly, taking the time and effort to ensure the best possible long-term conditions for it to thrive will pay off in the long run.

I don't know if this will be helpful to you but I read in some clematis book somewhere eons ago that the best time to prune clems was the same time you prune roses.........or when the forsythia is in bloom (as an indicator plant) and I have always followed that practice. In my climate, that is typically around President's Day or the end of February. I noticed that several of mine are already pushing a lot of new growth so I need to get out there and get whacking!! I tend also to be flexible about the exact timing. February can be cold in my climate as well and is always wet......and I don't do rain :-)) So I wait until a break in my schedule and a decent weather day coincide and prune as many as I can then. I also prune both my type 2's and 3's as type 3's - down to the third set of buds or about 18" - simply because it is easier and I don't have to remember who is who :-) At most it will delay the bloom period of the type 2's slightly......a few weeks to a month. All of my evergreen clems or type 1's I don't prune at all except very rarely to control size and that is done after their early bloom cycle.

Everywhere is going to offer different growing conditions and that's going to affect the timing of flowering as well. Here it is almost September and my triternata 'Rubromarginata', 'Sweet Summer Love' and 'My Angel' are showing no signs of flowering yet. Durandii is my only 3 that is currently flowering and it will continue until October without any need to cut back. I will say that up until late July, our summer had been unusually cooler than normal but since then, we have had stretches of very warm - for us - weather with a higher percentage of upper 80's - low 90's than typical. If you have group 3's flowering as early as June, then by all means I would see if you can encourage a rebloom by some moderate pruning. I'm not sure I'd be brave enough to cut back too severely. Wouldn't hurt the vine at all but I'd be afraid of eliminating any rebloom.