Ginny, I have grown clematis into several other vines with no problems.

One thing you have to remember. Huldine is cut back to 12" to 18" every winter. The only problems is pulling the dead vines of Huldine out of the other vine without hurting the other vine. Other than that you are good to go.

Katie

Thank you Katie for your advice. I don't want to be on a ladder removing the old vines so I found another spot for it which will be great I think.

Ginny

I would have responded sooner but I only just discovered what type of beast a lavender trumpet vine was :-) We can't grow those in my area and I was unfamiliar with the plant.

I'm glad you've found another spot for the clematis because I would not recommend planting the two together. The trumpet vine, Clytostoma, is a vigorous, rapidly growing evergreen vine and IME, very vigorous vines, especially evergreen ones, do not make good companion plantings for clems. It is difficult to get the clem established close to the already established trumpet vine and its large root system. And the evergreen vine often easily overwhelms the more delicate and deciduous clem. Plus, it is very difficult to untangle and prune the clem successfully once the vines become intermingled.

About the only time I would consider attempting this type of combination is if the vines were planted simultaneously and if the clem was itself a vigorous, large growing species that did not require pruning. A montana comes to mind but the bloom season would be nearly identical so still not a great choice :-)