Debbie, mine grows in a large pot topped with gravel mulch. It shares the pot with two hirsutissimas and a fremontii. Hardiness ratings are not known with any certainty for most clematis. You basically see on most varieties as them being hardy from zone 4 to 9. The Toomey and Leeds Encyclopedia of Clematis lists it as being hardy from zones 6 to 9 but I have found some of the hardiness data in that book to be totally incorrect(they may be more related to hardiness zones and winter weather conditions in England than the US).

Just realize that where a species clematis lives naturally does not mean that they can't grow in other types of conditions. If you are worried about it as far as hardiness goes in zone 6a (mine has survived outside in zone 7a in a pot now), you could always grow it in a pot and move it into an unheated garage once it goes dormant and the weather turns and stays cold in your zone 6a garden.

As another option, you may wish to contact Dan Long at Brushwood Nursery in PA because he grows it (not sure if he does outside or not) and may be able to give you more information relevant to your gardening zone.

Hope that helped some.