Newly transplanted clematis vines should be pruned to the lowest pair
of strong buds to promote a thicker more vigorous plant. Subsequent pruning
is based on when a particular species flowers. Those that flower on current
season's wood (Clematis x jackmanii, C. paniculata,
C. tanguitaica, C. orientalis, and C. viticulla)
should be severely pruned in late winter to early spring to promote new
growth. Large-flowering hybrid cultivars in this group include: Gravetye
Beauty, Etoile Rose, Ernest Markham, Hagley Hybrid, and Pere d'Azur.
Clematis that flower on one-year-old wood (Clematis florida, C. patens, C. montana, C. chrysocoma, and C. apina) should be pruned to develop a framework. Annual pruning consists of cutting away all flowering wood to within a few inches of the main framework immediately after flowering. After five or more years some clematis vines may become too tall or leggy and severe pruning may be required to rejuvenate the plant regardless of species. A third group of clematis includes most of the popular, large-flowering cultivars such as Nelly Moser, Henry, Duchess of Edinburgh, and William Kennett. These clematis flower in the spring from one-year-old wood, but also produce side shoots that produce further displays of medium-size flowers during late summer. The growth habit makes this group difficult to prune. They may be left unpruned or lightly pruned. When they become straggly or out-of-control, severely prune in late winter to early spring (spring flowers will be eliminated, late summer flowers should develop). An alternative is to severely prune one-forth to one-third of the oldest shoots back to within a foot of the ground each year for several years. This system works well for vines grown on walls and fences where shoots can be separated but poorly for vines grown on mailboxes.