Your C. petriei is a Type 1, early blooming clematis and doesn't require pruning, since it blooms on the previous years growth. If required for habit (maintenance and growth direction control) it may be pruned soon after blooms are spent. Severe pruning can remove next years bloom junctions... It doesn't like wet feet, but is reasonably hardy. Mulch its roots as you would any clematis... If, after three years or so, you want to transplant part of it, you can do so by dividing the rootball.
Best of luck!