Class 1 clematises want no pruning at all. Eventually they may need a very serious haircut but in the meantime, no pruning. Ours is here over 20 years and only now needs the serious trim.
Class 2 are the late spring bloomers like Pink Champagne, Fireworks, and so many more - probably the most popular class of clematises. Everyone seems to have their own method for pruning them. You'll see on various sites to prune them by half after they bloom, or prune by one third, or there are some people who will prune to the bottom set of buds in Feb/Mar/Apr. I prune down low in early spring for most of them but only because I don't want broken stems (can lead to problems).
Class 3 - be brave and prune down to the lowest pair of buds in Feb/Mar/Apr and have no fear. They zoom back into growth so fast and consume things like my light post.
