Question: I know there are three types of clematis. And that the specific type determines when the clematis should be cut down. Can you give some direction as to when each should be cut, and perhaps what some of the most common varieties are?
Answer: Clematis is a popular flowering vine. Most of the common species are fully winter hardy here in Pennsylvania, and the plant makes a terrific addition to trellises, arbors and pergolas.
You’re correct in saying that clematis can be categorized into three different groups, and the best pruning technique for each variety depends on which group it fits in.
The three groups are largely based on the bloom time of the variety.
Here are details on the three groups:
Group 1. Early flowering clematis: Species in this group include C. alpine, C. montana and C. macropetala. They produce their flowers in early to mid-spring. The flower buds, however, are produced the previous growing season. If you prune clematis in this group in the fall, winter or spring, you’ll be cutting off all your flower buds. Group 1 clematis should be pruned immediately after they flower.
Group 2. Mid-season flowering clematis: Species in this group include most of the large-flowered cultivars that produce double or semi-double flowers. They bloom in mid-summer. Members of Group 2 often produce a second set of blooms in the late summer on new wood that grows during the current season. Most have two separate flushes of flowers, with the second being less prolific than the first.
Common species and cultivars in this group include “Nelly Moser,” “Niobe,” C. florida and “Henryi” among many others. Since their initial flower buds are produced the season before they open, pruning of Group 2 clematis is best done after the second flush of flowers has finished. Do not prune this group too hard. Light pruning is best. Only remove dead wood and spent flowers.
Group 3: Late-blooming clematis: Species in this group include sweet autumn clematis (C. terniflora), C. recta, C. tangutica, and “Jackmanii.” This group flowers on new growth produced earlier in the same season. Pruning this group back to 18 inches tall stimulates lots of new growth and plenty of blooms. Though it may seem drastic, pruning these species back hard results in more flowers. Pruning should be done in the early spring.
While having these three groups is great for informing you on the best pruning technique to use, the main issue is that plenty of gardeners either don’t remember the name of the clematis they have, or they never knew it in the first place. For those who don’t know which clematis they have, watch the plant carefully to see where the flowers are produced and what time of year they come into flower to determine their group.
Or, alternatively, you can hedge your bets and go with the following general pruning technique that works for most species, regardless of their group. Head out in the early spring and carefully examine the vines. Look for swelling buds that have started to develop new growth. Start at the outer end of each vine and follow it back to the uppermost growing bud. Cut the vine back to just above that bud. Continue pruning off all the vines back to the uppermost growing bud.
Though this technique might translate to fewer blooms, it’s a safe bet for all varieties.