Gardener’s Mailbag: Clematis

Rose from Windham asks “What do I do with my Clematis? How do I prune it?”

One of the most desired and often most elusive garden plants is the Clematis. When planted in the proper spot, these beautiful vining plants will thrive and live for many years, but finding that proper spot can be a definite challenge. One of the best attributes of clematis is the sheer quantity of blooms that appear on such a delicate frame. This makes them excellent candidates for inter-planting with other shrubs and plants, as they will not “strangle” or overpower them. A classic combination is a climbing or rambling rose paired with large-flowered clematis, running all over a stone wall. They thrive in either full sun, or as little as 4 hours of direct sunlight per day. Some of the paler pink varieties benefit from more shade, and will reward you with brighter colored flowers. Blooms come in nearly every color except orange, and range in size and form from very tiny, bell-shaped flowers (C. ‘Rougchi’) to the very large deep purple blossoms of the Jackman hybrids.

For planting, clematis need a cool, deep root run, with plenty of water and good organic matter and regular, balanced feeding. A handful of bone meal mixed in with plenty of compost or well-aged cow manure goes a long way. In our cold climate, the crown of the plant should be at least 4″ below ground level. This will allow the plant to recover should it accidentally be weed whacked or damaged by animals. A shallow-rooted shrub or low perennials planted near the base of the clematis is beneficial, as it will shade the roots and crown and help keep them cool and moist. When training these plants, they need to be given proper support. Some varieties are much more vigorous than others, and as such will require a stronger trellis. These plants climb by twining their leaf petioles around their supports, however, so the structure must be strong but thin. Be sure to leave 3 to 4 inches of space between the support and any walls for good air movement to prevent disease and pest problems.

Pruning clematis is one of the most confusing aspects of growing these plants. To prune, or not to prune… the worst that can happen from improper pruning on a well-established plant is that you will simply delay the flowering. Clematis do not ever have to be pruned, either, but their flowering and display will be much better if they are. If properly situated and healthy, even if the plant is chopped clean off at the surface, new shoots will soon come from the crown and begin re-filling the support space. In the first spring after planting, all clematis should be pruned so that there are only two or three sets of buds above the soil level. This will ensure a good, fresh start for your new plant. Blooms may be sacrificed fro this first year, but it will be well worth the wait.

After the first year’s prune, find out which type of clematis you have. There are three basic pruning groups for clematis; those that bloom on the previous season’s growth, those that bloom on new wood, and those that bloom on both simultaneously. Typically in the northeast, we do not see the first type. Species like Clematis montana and its cultivars are medium sized blooms, occasionally scented, but the vine will usually winter-kill if temperatures reach below 0 degrees F, destroying any chance of blooms the following year. The second and third groups bloom on current growth, and as such are much better suited to our cold northern climate. The group that blooms on entirely new growth can be cut back to two or three sets of buds in early spring, and will grow and cover their support in a season. Clematis paniculata (ternifolia), or the Sweet Autumn Clematis, is an excellent example of this group. It flowers late, but the profusion of blooms is amazing. Most of the large-flowered clematis found in garden centers are of the type that blooms on both new and old wood. ‘Dr. Ruppel’ and similar types should be lightly thinned and pruned in early spring, with removal of weak and dead wood, and variation in the length of canes. This will allow the buds to develop and bloom first on the old wood, and a second set of blooms to appear later in the season as the new growth develops. If a clematis in this group has been severely neglected, cut it back hard. You will be rewarded with strong new growth that will flower profusely that fall. Just be sure to guide the new growth so it does not turn into a massive tangle of vines.

After the flowers go by, the seed heads that are left behind are generally quite ornamental. Wispy plumes appear where the flowers once were, and continue the interest through the rest of the year. Fall color is not spectacular, generally shades of yellow and occasionally orange. The beauty of the blossoms makes up for any of the plants’ potential shortcomings. No garden should be without one of these beautiful vines!