My most rampant grower is Sweet Autumn. It starts from 1 foot tall every spring and grows at least 20 feet up, making it dangerous to climb my deck stairs. It's not flashy, but would do a good job cooling the house, I would think. Mine has never reseeded and is not invasive, although some people say theirs do and are.

Thank you!

I ordered a couple from Donahue. I have a brick wall, would I need a trellis or would it climb up the brick with no problem?

It will not climb up the brick. Clematis leaf petioles need some support to wrap around.

I have a Emilia Plater that was planted in the spring of 2010 as a two year old plant. It is now at least 10 feet tall and 3 feet wide and covered with light lavender-blue flowers that show no sign of slowing down after 3 weeks. If it is this vigorous as a three-year-old plant during its second season here, I have a feeling that it will grow to be a quite large plant, despite CotW saying it is 3 meters tall.

Make sure that your trellis has narrow bars or wires, not thick lattice so that the clematis can successfully climb it. I have seen other folks refer to a wire trellis that attaches to brick from Lee Valley. Everyone I have seen commenting on it has been pleased with it, but I have no experience with it.