Help with Clematis

We have had a clematis for about 20 years. It has wrapped itself around an Oak tree in our garden (the stem is about 2" thick), it now flowers high up in the tree.

If we chop it hard back so it's about 6 feet tall will it continue to flower or will it kill it off?

Many thanks.

 

This link says it better than I could I think!

http://www.gardenersworld.com/plants/features/late-flowering-clematis/
Pruning late-flowering clematis

In order to keep the flowers where you can enjoy them, it's necessary to prune them back each winter. I do mine at the same time as I prune buddleias and roses, somewhere between mid-February and mid-March.


Cut them back to about 30cm from the ground, leaving two sets of healthy buds. Prune, and prune hard. It will mean removing a great mass of foliage, but nothing is lost, as none of it will produce a single flower the following summer.

 

Sounds very vigorous, like my Montanna, which I leave virtually well alone apart from the odd trim. The last one I cut back hard, years ago, died on me

 

I cut back Montana but still left some 6' stems and it came back better than ever. Trouble is I think you are a bit late. I would do it while it is still dormant in late winter, do it now will encourage bleeding.