There isn't one particular clematis that will bloom all summer..you can plant different varieties that will allow you to have one or the other blooming at sometime..Your Pruning group 2's will bloom once in Spring and then again in later summer/early fall..Your Montana's will bloom once in Spring..but what you must understand that when clematis do have their bloom cycle..it's usually for a 6 week period...your Viticella's/Pruning group 3's will be hard pruned and have to grow their new vines up before blooming as they bloom on new vines produced in the growing season..I get 2-3 bloom cycles from these by hard pruning and refertilizing again after their first intitial bloom period is over..you can check out COTW and it will list the bloom period and yes this is for the whole USA etc...the length of one's growing period attributes to variations in bloom periods but your zone isn't that much different from mine...I would plant various varieties to achieve this and once they are established you'll have lots of blooms ..I even had my Clematis "Florida Sieboldii" blooming in January this year!!...Jeanne

No Clematis blooms well the first year. They all take at least three years to reach maturity. They should be hard pruned the first two also to encourage more root and stem growth, which will reduce flowering but give you a much better vine over time.

June to September in the Pacific Northwest is significantly less hot and sunny than in Georgia. We only average a couple dozen days over 80* and you guys average close to 100, if I remember the chart I looked at the other day correctly.

This would definitely affect bloom time.

I think COTW is Clematis on the Web -

http://www.clematis.hull.ac.uk/new-clemalphasearch.cfm

I would look at Rooguchi for a long blooming clematis. I planted mine late last summer and this year they've completely covered a 7' obelisk by May and have been covered in blooms. I got mine from Plants Delight Nursery. They were on the more expensive side but they were so worth it.

Non-clinging clematis, Arabella, flowers in Montreal from mid-June to September here. But not in the 1st year, unless you find a mature specimen and even then.....

The same with nonclinging Inspiration. I have it growing on a trellis and tuck the vines behind each other for support . It blooms from June until a hard frost .

Bushy Blue bell is a shrub clematis that booms from early June until frost as well. This one I grow through a hatched support. It gets about three feet tall.

I also have an Arabella here in the Inland Northwest which blooms from June to frost.