Mine just had its first bloom open today. It too is an established clematis. So I wouldn't worry yet.

Hi
I just need to ask, did you fertilize with something high in nitrogin?I had this happen to me too much nitro and got all foliage.I would also say mabe the weather could be a little more extreme one way or the other

I have not fertilized it this year, nor did I prune it. Could this be why it is not blooming?

Yes...Clematis "Comtesse de Bouchard" is a pruning group 3 and should be hard pruned every late winter/early Spring..for it blooms on new wood..you won't see blooms on the old vines from last year...only the new growth it has produced this season..and you should fertilize with either Rose fertilizer or Tomato Fertilizer at the same time you prune it....Jeanne

Does that mean I can just prune it now and it will bloom? ALso what exactly is meant by "new" growth(i.e, is new growth only new growth that comes directly out of the ground? WHat about new shoots off of old vines for instance when I prune it 1-2 ft from ground?) Or should this thing be pruned right to the ground?
Thanks for the help!

New growth is growth from this season regardless of where it sprouts from.

don't prune now or you'll loose any chance to see any blooms this year.

next year, prune the entire vine back to within a foot off the ground in the late winter/early spring.

as for why it hasn't bloomed yet, maybe it's just late this year. also are you sure it hasn't gotten runoff from neighboring lawns that have been fertilized with high nitrogen fertilizer?