Released: March 05, 2004

Correct Clematis Pruning Depends on Bloom Type

MANHATTAN, Kan. – Gardeners who love showy clematis flowers can – quite rightly – be confused by current advice on how to prune the delicate-looking vines.

The problem is that this popular climber includes well over 200 species, in addition to many, many hybrids, said Emily Nolting, Kansas State University Research and Extension horticulturist.

“Fortunately, all of these clematis fall into two general categories, based on their blooming. And the categories indicate when and how you should do the majority of your clematis pruning,” Nolting said. “The two important exceptions relate just to new and sick plants.”

What’s probably the best-known category includes all the large-flowering clematis that bloom in May and June. Depending on variety, their blooms can range up to 6 inches across in an array of colors. The flowers can be single, double or both on the same plant. Some varieties continue flowering through the growing season, some bloom again in late summer, and some stop with their initial spring flowers.

“You prune this group lightly or not at all. You should remove any weak, dead or unsightly wood. You also can shape the overall plant – for example, to produce better spacing between stems or to reduce tangling, which sometimes can look a little overwhelming,” Nolting said. “You don’t remove anything you don’t have to, though, because these clemmies bloom on last year’s wood, not new growth.”

The recommended time for pruning large-flower varieties is early summer, just after the spring blooming period ends. This will result in healthier plants that bloom well the following year, she said.

The clematis varieties that produce the smallest flowers tend to grow the longest, lushest vines. Sweet autumn (C. terniflora) can grow up to 20 feet long and cover an arbor with tiny white flowers.

Small-flowering varieties usually bloom in late summer or early fall on new wood, produced earlier in the growing season. They can produce that new wood by extending on from last year’s vine output, but the result often is a “lollipop” with few leaves and no flowers from ground level up to the new growth.

“For thicker new growth – as well as to keep their length from getting unwieldy – you can cut these late bloomers 12 inches from the ground in early spring. This also should result in more blooms,” she said.

One exception to these rules is newly planted clematis, whether they’re spring or fall bloomers.

“The first spring after planting, you need to prune them hard – to no more than 12 to 18 inches from the ground. You won’t get any blooms that year, as a result, but this will encourage the plants to develop a stronger, more heavily branched base,” Nolting said. “If you’ve got an established clematis plant that’s well-sited, but not blooming well, you can take this same approach. The vine will grow back, rejuvenated, just as multi-trunked shrubs do when pruned hard.”

The other exception to the rules is the situation created by a fungal disease called stem rot or clematis wilt. The disease tends to be the plant’s most severe pest problem and can be particularly pronounced in young plants and some of the large-flower hybrids. It blocks a plant’s access to water from its roots; so, the clematis severely wilts or collapses – sometimes in a single night.

“The disease is really dramatic. But it’s usually not fatal unless a gardener decides the wilted plant is dead, so digs it up,” Nolting said. “Instead, you should cut the plant back, one or more inches below the wilting in what appears to be healthy tissue. Then remove the diseased vines from the garden and wait. Even if you’ve had to cut back to ground level, the roots usually will send out new, healthy spouts.”

Experts suspect clematis’ delicate-looking frame makes them susceptible to the disease. Those stems are easily damaged if not securely attached to a trellis or stake or if roughly handled during pruning.

“The resulting wounds are a perfect entry for fungi,” the horticulturist said.

Nolting’s “Garden Center Guide” about clematis is available on the Web at <http://www.oznet.ksu.edu/dp_hfrr/extensn/Hort_Tips/Perrenial_Flower/Clematis.pdf> .

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K-State Research and Extension is a short name for the Kansas State University Agricultural Experiment Station and Cooperative Extension Service, a program designed to generate and distribute useful knowledge for the well-being of Kansans. Supported by county, state, federal and private funds, the program has county Extension offices, experiment fields, area Extension offices and regional research centers statewide. Its headquarters is on the K-State campus, Manhattan.

Story by:
Kathleen Ward
kward@oznet.ksu.edu
K-State Research& Extension News