Clematis: To Prune or Not to Prune

Jun 12, 2014

By Dale Odorizzi, Lanark County Master Gardeners

Few subjects in gardening are as confusing or as frustrating as the proper pruning of Clematis. Most modern hybrid clematis have complex parentage with many combined strains that have contradictory pruning needs.

As Yogi Berra once said, you can observe a lot by just watching. The easiest way to determine the specific pruning needs of your clematis is to watch it grow through a season. It won’t harm your plant one bit to leave it completely unpruned for a season.

Group A - If it blooms only in April and May, it belongs to Group A. These plants flower on old wood. To prune this group, just remove any dead stems and weak growth as soon as flowering is finished. Clematis alpine and C. macropetala hybrids only grow to about 6 feet and should not be pruned too heavily or next year’s flowers may be lost. C. montana and C. armandii grow so rampantly they may need to be cut back yearly to keep growth manageable.

Group B—If a clematis blooms in May and June and again in September, it belongs to group B. This group have very large showy flowers on old wood in late spring and a smaller flush of flowers on the current season’s growth in late summer. ‘Nelly Moser’ is a good example of this group. Remove dead and weak stems in early spring, just as the leaf buds begin to swell. The whole vine can also be given a light pruning for shape then. Cut each stem separately, varying the lengths for a more natural look, rather than chopping them all off to the same height.

Group C - This group flowers in June or July and blooms almost nonstop through September. Their vines reach 10 feet tall. ‘Jackmanii’ is one widely grown variety. Since flowers on Group C are produced only on new wood or stems that grow each year, prune this group hard every year to stimulate fresh new growth. This means cutting back each stem to 2 strong sets of leaf buds just as they begin to swell in early spring. On established vines, prune to within 2 feet of the ground is sufficient. This hard pruning will guarantee flowers over the entire length of the vine. If Group C clematis is not pruned hard, it will still bloom but only on new wood which will begin growing where last year’s growth ended, leaving long, bare stems.

Late Bloomers are usually classed with Group C for pruning. Most popular is the hardy golden clematis which bears small yellow lantern shaped flowers from July through September, followed by attractive fluffy seed heads. These too can be left unpruned to cover a fence or sprawl across the ground.

An overgrown or neglected clematis of any type can be invigorated b pruning hard, at whatever height you like as long as some leaf buds remain, in early spring. New growth will appear quickly, thanks to the vines large, established root system. Flowers may not appear until next season if it is the type to bloom only on new wood.

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