Answer: While clematis would certainly climb up your Italian cypress, it isn't a good idea to encourage one to do so. The vines will shade the foliage of your cypress and eventually cause dieback, either from too much shade, too much moisture being held against the cypress, or from insect infestation. If you want to grow clematis near your cypresses you could place a trellis in front of the trees for the clematis to grow on. This will maintain good air circulation for both the cypresses and the clematis, and will allow you to keep the clematis vines under control so they won't overtake your cypresses.
Best wishes with your landscape.
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