I am sorry I cannot help you, but I have never started clematis from seed because I am to impatient. I believe it takes several years before they will bloom. I have a clematis in my garden that has come back for at least two years that I think has come from seeds that have self-sowed. Since it is not in the way I am going to let it grow and see what might bloom.

Good luck in your search for information. Have you googled your question?

Jane