I don't know about those vines exactly, but I did plant an annual vine, a couple summers ago, that choked the other plants in the container I had it with. There was very little doubt in my mind as to what was going on, the other plants were dying at the exact point that the vine was climbing on them. So that does not sound out of line to me.

Don't know if that helps or not, but I think I'd relocate the clematis. Nice blooms along a dead vine are just not good to look at. Helen.

Thanks, heleninramsey! But I'm stumped. Every internet site I've searched talks about clematis and creeper living harmoniously. (There are pictures!) Guess I'll go day by day to see it the clematis is really hurting the creeper, unless I hear from others who have experience with these plants.

Virginia creeper (Parthenocissus quinquefolia) is such a vigorous vine compared to any clematis (except the autumn blooming clematises that die back to the ground each year) that I can't believe your conclusion is correct. Besides, Virginia creeper is a vine, why isn't it taking over the clematis? This is what I would expect would happen.

There must be something else going on. Is it in a hot area? VC doesn't like hot, and perhaps more so than clematis, even though it can take full sun easily.

Frankly, I would rejoice in the results. Clematis are much nicer and more refined vines.

The v. creeper has been great to provide a dark background to a fence. The clematis was planted to liven it up a bit. I'm watching it daily and have decided to let nature take its course. Perhaps the dying off is natural; the rest of the creeper seems as healthy as ever, and the clematis is also healthy, so... We'll see! Thanks for the comments. I'll post an update for others.