Clematis Questions

clematis integrifoliaShown: Clematis integrifolia Petit Faucon (‘Evisix’)

Our Smart Gardening Online Workshop on Gold Medal Perennials prompted the following clematis questions from the audience for presenter Kerry Mendez.

Is there a clematis that will grow in the shade?
In general clematis prefer sun, but some will tolerate part shade. Kerry notes that ‘Comtesse de Bouchaud’ is one. Additionally, cultivars of C. montana, C. alpina, C. viticella and C. macropetala also take part shade. However, it is in warmer areas, the southmost end of their growing range, that you’re more likely for success when siting these in part shade. In the north, recommendations for full sun should be followed more closely.

How do you tell if you have a Group 3 clematis?
Clematis—of which there are hundreds of species and cultivars—are organized into three groups, the common denominators being their pruning and cultivation requirements. If you know the name of your clematis, you can look it up—a comprehensive clematis book will note its group. If you don’t know the plant’s name or you can’t find it referenced anywhere, you can take an educated guess following the below rules:

Group 1 Clematis
—Evergreen or deciduous plants that flower in winter and/or early spring on shoots that developed the previous year.
—C. alpina and C. macropetala and their cultivars, which bloom on the previous year’s shoots in spring and also sometimes on new growth in summer.
—C. montana and its cultivars, vigorous deciduous climbers that bloom in late spring on shoots that developed the previous year.
Prune Group 1 clematis after they flower, removing dead or damaged stems and otherwise pruning for shape and space.

Group 2 Clematis
—Deciduous clematis with large flowers that appear in late spring and early summer on side shoots stemming from the previous year’s growth.
Prune Group 2 clematis in early spring before growth resumes. Cut off dead or damaged stems and trim the rest back to where you can see strong buds. These buds will develop into “second-year shoots” from which flowering shoots will grow in later spring.

Group 3 Clematis
—Deciduous plants that bloom in summer and/or fall on the current year’s growth.
—Herbaceous clematis (die completely to the ground over the winter) that bloom from midsummer to late autumn on the current year’s growth.
—Clematis texensis—a US-native clematis—and C. viticella and their cultivars.
Prune Group 3 clematis in early spring before growth resumes, cutting the previous year’s growth back to a pair of strong buds about 8 inches above ground level.

I have sweet autumn clematis on an arbor. This last year it really grew to fill one side of my arbor. I am afraid that if I prune it I will not get the length of growth over my arbor. Should I prune it anyway?
“This is a very fast-growing clematis,” Kerry says. “I whack mine down to within 3 feet of the ground each spring and it shoots up and over my peegee hydrangea tree (which is over 6 feet tall) and across my five-foot cedar fence. I find I need to rein it in or it goes crazy. If you are nervous, do a light prune on it in late winter/early spring and see what happens.”

Editor’s note: Sweet autumn clematis (C. terniflora) is listed as an invasive plant in much of the Southeast. It spreads by seed. Read about this plant at the Invasive Plant Atlas of the United States.

Clematis virginiana is a US-native species that has similar ornamental appeal but it does not spread as vigorously. It occurs naturally in the eastern half of North America. Although it doesn’t spread as rampantly as sweet autumn clematis, some describe it as aggressive.

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