Short answer -- no :-) The plant does divert some energy into developing seeds but not enough to worry about w/ regards to additional growth and flowering.

Here's the response I gave to this same question asked a couple of years ago: "Seedheads of clematis tend to be as appealing to many growers as the flowers - they are great in arrangements, especially late season ones that can be left to dry. With the exception of some of the group II's that will produce a later summer rebloom, deadheading does NOT encourage additional blooming. And deadheading in that case has exactly the same effect as a light pruning after the first bloom flush.

Botanically speaking, flowering plants do not uniformly benefit or have a greater/extended flowering period if one deadheads spent flowers. This tends to be restricted primarily to annuals or single season plants that are genetically programmed to reproduce in a very short time frame. Deadheading eliminates or reduces seed production so the plant tries mightily to overcome this need for reproduction and self-perpetuation by producing more flowers that will hopefully mature into seeds. We humans have some how adopted the practice of deadheading and applied it to all plants thinking it will increase flowering when it is mostly a cosmetic effect. But perhaps the clearing away of spent flowers/removal of seedheads gives the appearance of allowing the plant to produce more flowers :-))"

Wow Gardengal you are so much help! I really appreciate all the wisdom you give me! I have 5 different kinds of clematis and they all bloom again after their first bloom. But nothing like the first bloom. I have started to dead head them the last two years thinking that would help. I enjoy the spent blooms also and hit me today that my dead heading might not be doing anything to help the cause. I will stop!!! Thanks again!!!