I'm so glad you said that because a bunch of mine are doing the same thing. I've never seen it before and I didn't do anything different this year. I've been trying to think about how the weather has been this year to see if that might be the reason. We are low on rainfall to judge by the state of the rivers around here, but it seemed to rain often, if not a lot, all summer. Then there was the really early heat. It's kind of too bad if it isn't anything I can control, because I was really hoping that it was just that the clems were getting more mature and they would start to do this every year, but if it's new for you, probably not.

There are many varieties of clematis that bloom in the spring and again in the fall. Some people trim P:2's by about a third to help with new growth and bloom in the fall.

My P:2 clems are only two years old so don't know how they will respond most years. Many of them are blooming again now.

I do get fall blooms sometimes on my PJM Group Rhody and Night Editor is blooming right now.

I did get a few on Clematis Ramona this year which was a first. Normally, I get another burst on Daniel Deronda but this year he didn't stop during summer and bloomed from April to the end of August so I don't expect anymore.

I'm having the same thing happen to two of my clematis that were the worst hit by the severe drought and high temperatures we had this past summer. I'm in zone 6b on the east coast and these two clematis had gotten wilt (I thought) and died back to the ground. I left them alone thinking I would prune them hard next spring. Now that it is fall we are getting plenty of rain and they are coming back just like they would if it was spring.

I think what has happened is that the heat drove them into dormancy and that may be what happened to yours as well. Now that the weather is cool and wetter (not unlike our spring) they think it's time to grow and bloom again. What I don't know is if this will weaken the plants later on. Of course pruning them will only encourage them so I think we just have to let nature take it's course and enjoy the second set of blooms.

kathryn, it's funny you should mention that, because I have a clem doing the exact same thing!
I pruned it back after blooming though, in June, and it has not started coming back at ground level until now! I saw two or three little green nubs poking out of the ground now. Hmmm.. I hope they don't start to think it's spring, try to grow and get zapped by the cold frosts. The one that's doing it is Franziska Maria. All the rest I pruned down also, but they came back up already.
I must have pruned too hard, but what the hey! They can take it! lol FM was too scrawny, and I thought if I hard pruned her then she'd come back over summer a little stronger and fuller. Now, she thinks it's spring and tries to poke out of the soil! Go back to bed little clemmy! It's not time yet! lol

Cathy