There may be no prettier climbing plant than the clematis. These hardy vines clamor over trellises, fences, and even trees and shrubs. They produce flowers in three general forms: small white flowers (now a purple variety as well) in panicles or loose irregular spreading clusters (generally autumn blooming), bell or urn-shaped flowers, and flat open flowers. They have four to eight petals and come in an array of colors. Most gardeners plant clematis knowing that they prefer full sun and a thick layer of mulch to keep their roots cool in the summer, however, very few gardeners know how to prune these beautiful vines.
The main purpose of pruning clematis is to maximize flower production. Generally, it is a good idea to prune your clematis annually however timing will vary with variety. There are three major methods and classifications for how and when to prune depending on when your clematis flowers. If you don’t prune your clematis at all it will still bloom, however, the blooms will be at the top of the plant out of sight.
Clematis that bloom in early spring (April and May) flower from buds produced the previous season and are called group A clematis. This means they flower on old wood and should be pruned once immediately after flowering. If your prune in the spring, you will remove your flowers. By pruning immediately after flowering allows for the new growth to harden, age through the growing season, and set flower buds in the fall for early spring flower. To prune group A clematis cut outshoots that flowered previously in the spring. You can prune out other shoots as well to reduce the plant size, however, leave large woody stems and trunks for new growth production.
Large, flowered clematis or group B, flower in mid-June on short stems from the previous season’s growth and again later in the summer on new growth. This clematis should be pruned in February or March to remove dead and weak stems. The remaining vines should be pruned back to the topmost pair of plump green buds. These plants tend to become bare at the base and can be pruned back to the base after spring flowering every few years to force more flowers at the base. You can also underplant with other flowers to hide the bare base.
Late flowering or group C clematis flower on the bottom two or three feet of the current season’s growth. Some will bloom in mid-June, and some will bloom into the fall. This is the easiest group to prune because old wood doesn’t have to be maintained for flower production. In February or March cut each stem to about two to three feet and prune out any dead or weak vines. Don’t prune again during the current growing season.
Clematis is a beautiful vine that is hardy and relatively easy to maintain with very few pests and disease problems. By following a few easy pruning steps your clematis will be the envy of the neighborhood!
Source: Dennis Morgeson, Washington County Agent for Horticulture