From the ArcaMax Publishing, Gardening Newsletter:
http://www.arcamax.com/news/gardening/s-156709-931058
Question: I just moved into a new home with a lovely clematis. It is
blooming beautifully. Should I plan to deadhead it once the flowers
fade?
Answer: It is not necessary to deadhead clematis--which is fortunate
because deadheading a mature plant would be a huge task! Many
gardeners find the seed heads decorative during the fall and winter
months, too. Enjoy your plant!