Hardy clematis vine can climb high in your garden

Wherever you need something colorful to clamber over something — a trellis, a fence, a shed, an arbor — there’s a clematis vine that would welcome the opportunity.

Several types of clematis are hardy, long-lived perennial vines that thrive in the upper Midwest. “Some of them thrive so well that pruning is in order,” said Spencer Campbell, manager of the Plant Clinic at The Morton Arboretum in Lisle.

The most familiar clematis blooms are the big purple saucers of Jackman’s clematis, a common sight in summer in Chicago-area gardens. “Hybrids of Jackman’s clematis are what usually comes to mind when ‘clematis’ is mentioned,” Campbell said.

Jackman’s clematis (Clematis x jackmanii) has been planted to climb the massive central arbor in The Gerard T. Donnelly Grand Garden at the Arboretum, and by mid-June some of the plants had climbed more than 6 feet. There are Jackman’s clematis hybrids that bloom in pink, red, and blue, as well as purple. In fall, the fluffy seed heads are also decorative.

“Jackman’s clematis prefers, but there are other species that need full sun,” Campbell said. All clematis like well-drained soil with plenty of organic matter. They prefer to have their roots cooled with an insulating layer of mulch, and often grow well with their roots shaded by other plants. “Cool feet, face in the sun” is a proverb often applied to growing clematis.

Although some cultivars (cultivated varieties) have been bred to stay relatively small for containers, most clematis need space and something to climb. They can often reach 10 to 20 feet if left unpruned.

A clematis vine climbs by twining its leaf stems around whatever it comes across as it grows. The vine does not need to be tied to the support, like a climbing rose. “It may need a little guidance so it only climbs what you want it to climb,” Campbell said.

Clematis will twine up the stems of a shrub, and the combination of clematis with roses is an English garden classic. Generally, the leaf stems need something narrower than a finger to wind around. A wire tower swathed in clematis can bring height to a perennial planting.

If you prune a clematis vine to keep it under control, timing is important. “Pruning at the wrong time could mean you’re cutting off flower buds,” Campbell said.

Some species and cultivars bloom on new wood — new stems that sprouted this year. Others bloom on old wood, meaning they develop flower buds in late summer or fall and carry them through the winter. “Read the plant label carefully when you buy a clematis so you will know whether to prune in winter or late summer,” he said.

There are about 300 species of clematis from around the world, including a few that are native to North America. Here are some lesser-known kinds of clematis that grow well in Midwestern gardens.

Durand’s clematis (Clematis x durandii): Somewhat smaller than Jackman’s clematis, this hybrid has cornflower-blue blooms that start in an urn shape and open to saucers.

Scarlet clematis (Clematis texensis): Although it is native to Texas, this species is hardy in the Chicago area. Its urn-shaped flowers are a vivid hot pink.

Virgin’s bower (Clematis virginiana): Native to eastern North America, including the Chicago region, this species has masses of fragrant, small white flowers in late summer. It may require pruning to control its growth.

Italian clematis (Clematis viticella): The lavender or purple flowers of this vine are shaped like hanging bells.

Sweet autumn clematis (Clematis terniflora): This nonnative species from Asia is not recommended. It is an aggressive grower that reseeds readily, and can quickly escape into nearby landscapes, including natural areas. “We don’t advise gardeners to plant it,” Campbell said. “If you already have some, then you should consider replacing it with a native alternative such as virgin’s bower.”

For tree and plant advice, contact the Plant Clinic at The Morton Arboretum (630-719-2424, mortonarb.org/plant-clinic, or plantclinic@mortonarb.org). Beth Botts is a staff writer at the Arboretum.