There’s a lot to like about clematis, one of the earliest vines to green up in the spring. It’s easy to grow, blooms in profusion and is hardy, with some varieties lasting over 50 years.
Yet there remains a great deal of confusion about when — or even if — these woody plants should be pruned.
“If you have vines that grow 20 feet a year, they likely will be blooming in your neighbor’s yard and not your own,” said Linda Beutler, curator of the Rogerson Clematis Collection at West Lynn, Ore., and author of “Gardening With Clematis” (Timber Press, 2004). “The reason for pruning is to keep them under control.”
The tops get bulky and the bottoms appear bare if you don’t prune clematis plants every two or three years, Beutler said.
“People like them to look green from the bottom up,” she said. “You have to prune them to keep them looking that way.”
There are more than 250 clematis species and even more hybrids. They are separated into three broad pruning groups, mainly according to when they bloom.
Clematis in Group A are the vigorous spring-blooming varieties that flower on stems produced the previous season, the so-called “old wood.” They include the “Alpina,” ‘’Armandii” and a number of the Montana varieties. They should be pruned as soon as they finish blooming.
Group B is the large flowered hybrids, such as the familiar “Nelly Moser,” ‘’Miss Bateman” and “Henryi.” They bloom in early to mid-summer, also on old wood. Prune the tops of these plants lightly in February or March, allowing them time to produce new stems for the next flowering season. The vines can be given a second and hard cutting immediately after flowering, down to a height of around 18 inches. That helps direct and support their growth, whether they are wrapped around a fence, pole or trellis.
Group C is the late bloomers, including the iconic “Jackmani,” the “Perle d’Azur” and “Duchess of Albany.” This collection blooms on stems formed during the current growing season, and should be pruned in late winter or early spring.
People new to gardening often are intimidated by pruning, but the clematis groupings are pretty straightforward, said Sandy Feather, a commercial horticulture specialist with Penn State Cooperative Extension in Pittsburgh.
“If you know which cultivar you have, (then) a lot of charts on the Internet can help show you when you should be pruning,” Feather said.
With clematis, you ignore pruning at your peril, said Dennis Patton, a horticulture agent with Kansas State University Research and Extension at Olathe. “Left untended, they will grow into a tangled mass of vines mixed with new growth. They will be unruly looking. Difficult to manage,” he said.
Pruning the tops of the plants brings blooms back down to eye level, Patton said. “If in doubt, don’t prune before flowering,” he said.
There are many ways to kill clematis, but pruning isn’t one of them, Beutler said. “Even if you prune at the wrong time, the only thing that will happen is that you’ll set the blooms back by a year.”
For more about growing and pruning clematis, see this Ohio State University Extension fact sheet: http://ohioline.osu.edu//hyg-fact/1000/1247.html