Clematis vines come in a variety of species and hybrids that all benefit from annual pruning. If you want to cut back a vine without decreasing the number of flowers it will have, observe whether your vine blooms on this year's or last year's growth. Clematis vines that bloom in late spring or early summer or that produce large flowers in mid-summer usually bloom on last year's growth. Small-flowered ones that bloom in the fall usually bloom on the current season's growth.
Blooms on Last Year's Growth
Prune off the branches that have already bloomed soon after the flowers fade, using hand pruning shears.
Cut back the remaining small branches as necessary at the same time to prevent the vine from growing too large for its space. Avoid cutting off the woody main stem, since it will grow back more slowly.
Prune off dead or damaged stems in late winter. Cut them back 1 to 2 inches beyond the last pair of large healthy buds.
Blooms on This Year's Growth
Cut back the vine in winter or early spring before it begins growing. Trim the main stems to 15 to 30 inches above the ground, severing them 1 to 2 inches beyond the last pair of healthy buds.
Inspect the vine before it begins growing in the spring if you pruned earlier in the winter, and cut off any damaged or dead stems 1 to 2 inches beyond the last healthy buds.
Renew the vine if a severe winter has killed back most of it or if it has become too leggy, by cutting it back to a few inches above the ground. The vine will regrow much of its height the first summer but may not begin blooming again until the second summer.