They can be pruned now without harming the plant. It's up to you. You can go ahead and enjoy the bloom and cut them back early next spring or cut them back to eliminate the bare stems.

That is what happens when you don't hard prune pruning group 3's for they bloom on the new vines that are produced in the growing season..they will only bloom at the top where the new vines have formed..Hard prune down to the first leaf nodes...and do it each late winter/early spring..same time you usually prune your Roses or when the Forsythia's are in bloom...Jeanne

I am in central NH, just north of Concord. For this year you could hard prune some of the vines to the first or second node - they may still bloom as most of my vines in central NH are 3 feet or less right now from their pruning. Leave the rest of the plant unpruned for this year so you get at least some flowers in case the pruned ones don't bloom and then prune the whole plant next winter (and each winter after this as Jeanne said) to get the whole vine blooming.

Ok. I will prune them to the first leaf nodes and give them a hard prune next year. Thank you all for your advice.

Just to make sure everyone is on the same page.....when you are advised to prune back to the first or second leaf node, that is measured from the ground. And that IS considered hard pruning :-) I think nhbabs was suggesting that if the vine has multiple stems, you could hard prune some and leave the rest. That should help to increase fullness through the body of the plant and quite possibly still result in flowering on the pruned growth.

However, if the clematis have never been pruned since you planted them, chances are very good they won't have a lot of stems emerging from the root crown... maybe even just a single stem :-) You can still prune now if you wish - at this point in the season, there should still enough time for a type 3 to produce flowering growth. You just may not see flowers until quite late in the season.

Thanks for clarifying, GG. That's exactly what I meant.