Can't remember if I've ever seen this done, might be some problem with twining shoots of clematis going around new growth of rhododendrons and deforming it. Their densely sod-like roots also not much suited for adding new plants among them.

Might be better to plant the clematis between the rhodies (unless they already overlap to a large degree), use a small trellis, and coax the clematis to drape out over the rhodies.

This would make annual pruning of both easier also.

I have the same type of aged rhodie-tree and have had a clematis growing up it for about ten years now. It looks spectacular, I'd have to say! It really is the star of the garden for most of the summer. And it makes such better use of the space instead of just the 3 weeks or so that the rhodie itself is in bloom.

The clematis is a jackmanii or something similar that an old neighbor gave me cuttings of long ago. Pruning has been easy; I just stand under the rhodie and yank down all the vines sometime in the winter, cut them off at the base and stuff in them into the yard waste bin. A few stragglers in the high branches I need to poke with a rake handle to get down, but that is it.

Now for the downside. The clematis has gotten really big and this year I noticed weak growth and a little bit of die back way on the top of the rhodie's crown, probably because the vine blocks too much light. I need to make a decision soon about whether to pull the clematis (I don't think I want to do that yet) or prune it so it doesn't cover as much of the crown (I don't think I can do that since I hack it back to a stub already - maybe by a lot of thinning). I don't want to injure or deform the rhodie, though, so I need to do something. Suggestions are welcome. :-)

You are having the exact experience I anticipated and was talking about earlier. If it had not been a type you cut down each spring the situation would probably be far worse. Maybe the previously mentioned idea of growing it on a support near the rhododendron, rather than on it is the way to go.

Sorry, bboy, but it is different. I don't see any problems from twining; the clematis that I have doesn't twine. It climbs by just reaching or scrambling up. I believe the problem is from the light being blocked. The affected rhodie branches aren't deformed, but they look like ones that are in too much shade or are in the interior of a dense bush.

I also don't quite see how a support would help. This rhodie is the size of a small tree and a support would have to be huge to keep the clematis from reaching from the support over to the rhodie. I don't have the room or the desire to build the Eiffel Tower in my backyard. A shorter support would keep the clematis from the lower part of the rhodie, but there is no problem there since it is a bare trunk. And it would still eventually part ways with the support and climb in the upper parts, where the problem is.

I grew a clematis up a rhodie at my last house. Loved it. They both thrived. I'd say to go for it, and pull it out if you don't like it. 8-)