I have always disliked this plant, while I know others must love it. I have no doubt it would succeed, being almost impossible to get rid of, once it gets going. Would the rarer and,unfortunately, more expensive, Clematis armandi live in your zone? It is evergreen and has nice smelling flowers earlier in the year. Visit the website of gardenvines.com to see a huge selection of nice vines, as alternatives. I am only a satisfied customer of theirs, not a spokesperson.

Zone 6 is pushing it for clematis armandii. It used to get severe wind burn in the winter in my zone 7a garden in NC. I agree that SAC is just too rampant and spreads like a weed, seeding itself everywhere in my garden. One way to prevent the seeding is to chop the vine back severely after the plant's blooms have faded or take a hedge clipper to it to remove the developing seeds.

Good luck trying to contain its growth. How do you plan to have it attach itself to the underside of the supports?

Actually, I'm looking for an aggressive grower to cover the entire pergola. I plan on using fishing line under the "eaves" of the pergola. If I create a criss-cross pattern, should that be enough for the vine to grab onto and support itself?