Clematis

Prepared by Karen Russ, HGIC Horticulture Specialist, and Bob Polomski Extension Consumer Horticulturist, Clemson University. (New 09/99. Revised 09/07. Images added 09/07.)

HGIC 1104

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Clematis are among the most decorative and spectacular of all the flowering vines. They are a varied group of mostly woody, deciduous vines, though Clematis armandii is evergreen and a few are herbaceous perennials. There is great variety in flower form, color, bloom season, foliage effect and plant height. There are clematis species and cultivars suitable for all areas of South Carolina.

Clematis armandii, an evergreen clematis, in late March.
Millie Davenport, ©2007 HGIC, Clemson Extension

Height/Spread

Size of different clematis varies considerably. Very vigorous species like Sweet Autumn Clematis (C. terniflora) and Anemone Clematis (C. montana) grow to 20 to 30 feet. Most of the large-flowered hybrids grow to around 8 to 12 feet tall, and the small herbaceous species grow 2 to 5 feet tall.

Growth Rate

The old saying about clematis growth is, "The first year they sleep, the second year they creep and the third year they leap." Growth may seem slow as the plant builds its root system, but once established, clematis are strong growers.

Ornamental Features

Hybrid clematis vines are spectacular, with a profusion of flowers in white, blue, violet, purple, pink, red and bicolors. The large-flowered hybrids may have blooms ranging from four to ten inches in diameter and as many as 100 or more blooms per plant in a season.

There are three general flower forms: small white flowers in loose clusters; bell or urn-shaped flowers; and flat or open flowers. Many of the species have fragrant blooms, which is not true of most hybrids. Small-flowered species offer a range of fragrances from almond to hot cocoa.

Hundreds of species and thousands of varieties are available. Their bloom time ranges from February or March until frost. The fruit is often showy as well, being a ball-shaped, "feathered" structure. As cut flowers, clematis are long-lasting. The seedpods are used in dried flower arrangements. Butterflies and hummingbirds are attracted to clematis.

Feathery, ball shaped fruit forming on 'General Sikorski' clematis.
Karen Russ, ©2007 HGIC, Clemson Extension

Problems

The most devastating problem of clematis is a fungal stem rot and leaf spot called clematis wilt. The plant or part of the vine collapses suddenly and within a few days, the stem and leaves turn black and die. Cut off and destroy all the affected parts. If you have planted your clematis with two buds below the ground, it will usually grow back from the base the following year. Plants in their first year of growth seem to be more susceptible than established specimens. This is a disease mainly of large-flowered hybrids. Small-flowered hybrids, the species and their cultivars are less susceptible to wilt. Try the lovely s mall-flowered species if you have had trouble with wilt in the past.

Powdery mildew may occur, often on plants in areas with poor air circulation.

Aphids may feed early in the season on new growth. Mites cause a fading of green leaf color, making the leaves look dusty or yellowed. Slugs may attack newly planted plants or even feed on the bark of young stems. Rabbits and mice may feed on stems, girdling them.

Despite this list of potential problems, most clematis are trouble-free once established.

Landscape Use

Clematis have a dense mat of leaves that is ideal to shade porches. They are excellent for use on trellises, fences and walls.

Clematis like to be grown with "their heads in the sun and their feet in the shade." Clematis need at least 6 hours of sun to flower best, but in South Carolina they will benefit from some shade during the afternoon. Flowers of some red, blue and bicolored large-flowered hybrids fade if they get too much sun. These should be planted in eastern exposures or partial shade.

Though the plant's stems and foliage should be in sun, the roots like a cool, moist environment. The soil should be kept cool and shaded by low groundcover plants or perennials that have shallow, noninvasive roots. A 2-inch layer of mulch or stone paving also provides a cool root environment. Most clematis can be grown here with protection of the plant base and roots from the summer sun.

Avoid planting in extremely wet locations. The site should be open enough to allow for air movement around the plants, but protection from strong winds is also desirable.

With the exception of Anemone Clematis (C. montana) and Sweet Autumn Clematis (C. terniflora), clematis do not compete well with large tree roots.

Soil in the planting area should be prepared to a depth of 2 feet in an area about 3 feet wide. Incorporate one-third by volume compost or well-rotted manure to improve aeration and drainage.

After amending the soil for planting, dig a hole to accommodate the root system. Cut stems back to 12 inches in height. This will help the plant branch as it begins to grow and will reduce the chance of stem breakage during the planting process. Clematis are most often container-grown, as they do not withstand much root disturbance.

Plant clematis with the crown one to two inches below the soil surface. This allows the plant to recover should it be mowed off, damaged by animals or infected with clematis wilt.

Provide support for the vine. Supports must be thin since this plant climbs by twining the bases of its leaves around a support and cannot grasp thick branches or heavy trellising. Latticework or trellises can be used if placed a few inches from the wall for ventilation and if large enough to support the vine. Poles can be used for supporting smaller, less vigorous vines. Arbors are suitable for the larger, more vigorous types of clematis. Some gardeners choose to let the plants sprawl over the ground, over woodpiles and over other plants.

Water deeply once a week in dry seasons. Vines need at least an inch of water a week either from rain or irrigation. Renew mulch to a 2-inch depth in late spring after the soil has warmed unless a groundcover or other method is used to cool the root environment. Work a good general fertilizer gently into the soil surface in spring. Do not feed clematis during flowering. In the autumn, a mulch of well-rotted manure or compost will be beneficial.

Pruning

Clematis are divided into three groups based on the pruning methods used for each. The pruning method that is used depends mainly on the time of year the plant flowers. If you are not sure what group your plant is in watch it for a year to see when it blooms. Because vines will likely be tangled, and dormant vines may appear lifeless, make cuts carefully.

Group A Early-Flowering Clematis: Plants in this group bloom in early spring, generally in April and May, from buds produced the previous year. Prune these back as soon as possible after bloom but no later than the end of July. Do not cut into woody trunks. Plants in this group include C. alpina, C. macropetala, C. armandii and C. montana.

Group B Large-Flowered Cultivars: Large-flowered hybrids bloom in mid-June on short stems from the previous season's growth and often again in late summer on new growth. Prune in February or March by removing dead and weak stems, then cut back remaining stems to the topmost pair of large, plump green buds. This should be a fairly light pruning. Plants in this group include: 'Nelly Moser,' 'Miss Bateman,' 'Lasurstern,' 'Duchess of Edinburgh,' 'Mrs. Cholmondeley' and others.

'Nellie Moser', a group B, Large-flowered clematis.
Karen Russ, ©2007 HGIC, Clemson Extension

Group C Late-Flowering Clematis: Plants in this group flower on the last 2 to 3 feet of the current season's growth. Some types begin blooming in mid-June and continue into the fall. In February or March, cut each stem to a height of about 2 to 3 feet. Plants in this group include: C. viticella, C. x jackmanii, C. terniflora, 'Perle d'Azur,' 'Royal Velours,' 'Duchess of Albany' and others.

Species & Cultivars

Group A Early-Flowering Clematis:

Alpine Clematis (C. alpina) grows 6 to 8 feet tall, blooms April and May. Flowers are nodding, small, bell-shaped, lavender or purple-blue.

Armand's Clematis (C. armandii) grows 15 to 30 feet tall, blooms April and May. Two-inch creamy white blooms in large clusters; has a strong vanilla scent in warm weather. This vigorous evergreen clematis has rich green, leathery leaves. You can cut this vine to the base to rejuvenate.

• 'Apple Blossom' has flowers that resemble large apple blossoms, opening pink and fading to white.

Downy Clematis (C. macropetala) grows to 15 feet tall, blooms April and May. Flowers are nodding bells, 2.5 to 3 inches in diameter, pale blue with purple shading. These plants prefer cooler, shady locations and will grow best in the Upper Piedmont area. Named varieties may have double flowers; blooms may be shades of blue, pink or lavender.

Anemone Clematis (C. montana) grows 20 to 30 feet tall, blooms May and June. Produces masses of flowers in white or pink, 2 to 2.5 inches in diameter. Some cultivars have a vanilla scent. One of the easiest to grow, this vigorous plant develops strong, woody stems. Prune hard to limit growth.

• 'Rubens' and 'Tetrarose' both have flowers with a stronger pink than the plain species.

Group B Large-Flowered Cultivars:

Clematis lanuginosa 'Candida' features a burst of yellow stamens in brilliant white flowers that commonly reach 8 inches across. This plant produces flowers on graceful vines of old and new wood. Prune sparingly.

Florida Clematis (C. florida) features unusual flowers with big, creamy white sepals surrounding ornate rich purple and green centers. It is well-suited to warm areas.

• 'Alba Plena' has 3-inch double flowers in pale greenish white.

Large-Flowered Hybrids:

• 'Barbara Jackman' grows to 8 feet. The vigorous, bushy plant has flowers in May or June that are 4 inches in diameter, deep purplish-blue with bright magenta bar. They fade to mauve-blue.
• 'Hagley Hybrid' grows to 8 feet and flowers June to September. Flowers are 4 inches in diameter, pale mauve pink, fading to a washed-out pink. Vigorous grower, can also be pruned as group C.
• 'Henryi' is an old, vigorous and reliable variety that blooms for a long season, from early to late summer. It grows 9 to 12 feet tall, with large white flowers. Can also be pruned as group C.

Clematis 'Henryi'
Karen Russ, ©2007 HGIC, Clemson Extension

• 'Jackmanii' grows 8 to 10 feet, and blooms from July to August. Flowers are 4 to 5 inches in diameter and deep bluish-purple. Free-flowering.
• 'Marie Boisselot' grows to 8 to 12 feet, with flowers June to September. Opening flower buds are flushed with lilac-pink, flowers are 8 inches in diameter. Strong grower.
• 'Mrs. Cholmondeley' grows up to 20 feet. Blooms May to October with light lavender blue flowers, paler along the midrib. Can also be given group C pruning.
• 'Nelly Moser' grows up to 8 to 10 feet, with flowers from May to June and again in September. The flowers are 8 inches in diameter, pale rosy mauve with a central carmine-colored midrib and dark maroon anthers. The flowers fade badly in full sun; provide some shade for this plant.
• 'Niobe' grows 8 feet tall and flowers from June to September. Cup-shaped blooms open dark ruby red then turn to bright ruby red with cream stamens. First flowers are 6 inches in diameter, later ones 4 inches in diameter. Moderate grower with some bloom throughout the season.
• 'Perle d'Azur' grows to 16 feet. Flowers continuously early summer to mid-autumn. Blooms are 4 to 6 inches in diameter, sky blue with green stamens.

Group C Late-Flowering Clematis:

Sweet Autumn Clematis (C. terniflora) grows vigorously to 30 feet. This clematis produces a cloud of sweetly scented, cream-colored, inch-wide blossoms in early autumn. To control this aggressive vine, cut it back hard after flowering or in early spring. It is generally pest-free.

Sweet autumn clematis is extremely vigorous and fast growing.
Karen Russ, ©2007 HGIC, Clemson Extension

Orange Peel Clematis (C. tangutica) Small (2- to 4-inch) rich yellow blossoms of this clematis hang like little Chinese lanterns on stiff upright stems. After flowering, fuzzy silver seedpods hang on through winter.

Texas Clematis (C. texensis) A Texas native, this species will stand up to dry, hot summers. The foliage has a bluish tint. Plant it in a south-facing location with plenty of air circulation.

• 'Duchess of Albany' is the best-known variety, with large bell-shaped blossoms of deep rose.

Italian Clematis (C. viticella) grows 10 to 12 feet, blooms July to September. Rich, deep purple flowers are 1.5 to 2.5 inches. Vigorous and easy to grow. This clematis is tolerant of warm roots. It originated in southern Europe and western Asia and is adapted to a hot climate.

• 'Etoile Violette' has deep violet flowers.
• 'Alba Luxurians' is solid white.
• 'Mme. Julia Correvon' has wine red flowers.
• 'Polish Spirit' is a deep purple with cherry red stripes.

Large-Flowered Hybrids:

• 'Comtesse de Bouchard' grows 6 to 8 feet, with flowers July to August. This is an easy-to-grow prolific bloomer and a good plant for small spaces. Flowers are 4 to 6 inches in diameter, pink with creamy stamens.
• 'Vyvyan Pennell' grows up to 8 feet. Flowers are 6 to 8 inches in diameter, deep violet-blue suffused with purple-red and bloom in June and September.

Bloom Season

These clematis are listed in approximate order of bloom. Bloom times will vary from the coast to the mountains by as much as a month or more.

February into April:
Clematis macropetala

March into May:
C. armandii
C. montana

April into June:
C. alpina

May through August:
C. lanuginosa
C. viticella
C. 'Jackmanii'

Clematis Hybrids: Most put out a flush of bloom in May or June, then flower sporadically throughout summer.
C. 'Hagley Hybrid'
C. 'Nelly Moser'
C. 'Niobe'
C. florida
C. texensis

September into November:
C. tangutica

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