Early blooms. Lightly prune after blooming. This group of Clematis blooms in spring on the previous year's growth. Prune just after flowering by removing any weak or dead stems, then lightly shape and guide vines if needed.
Repeat bloomers with first flowering on previous year's growth, then rebloom on the new growth. In early spring, when buds begin to swell, lightly prune if needed to shape vines. After the first bloom, give another light pruning to increase later blooms.
Summer and later flowers on new growth. Hard prune in early spring as new leaf buds begin to swell low on the plant. Trim to 8-12" tall, to a pair of strong looking buds.