Clematis

Clematis are among the most decorative and spectacular of all the flowering vines. They are a group of mostly woody, deciduous vines, though Armand clematis (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.

Armand Clematis (Clematis armandii) is an evergreen clematis that flowers in late March.
Millie Davenport, ©2007 HGIC, Clemson Extension

Height/Spread

The size of different Clematis species varies considerably. Anemone Clematis (C. montana) is a vigorous grower that can reach a height of 20 to 30 feet. Most of the large-flowered hybrids grow to around 8 to 12 feet tall, but the small herbaceous species only grow to 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 white, blue, violet, purple, pink, red, or bicolor flowers. 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: flowers in loose clusters; bell or urn-shaped flowers; and flat or open flowers. Many of the species have fragrant blooms, with the exception of most hybrids. Small-flowered species offer a range of fragrances from almond to hot cocoa.

Hundreds of species and thousands of cultivars are available. Their bloom times range from February or March until frost. Butterflies and hummingbirds are attracted to clematis flowers. As cut flowers, clematis are long-lasting. The fruit is typically a showy ball-shaped, “feathery” structure. The seedpods are used in dried flower arrangements.

General Sikorski clematis (Clematis ‘General Sikorski’) has feathery, ball-shaped seed heads. 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 two fungi credited with causing clematis wilt are Phoma clematidina and Ascochyta clematidina. With this disease, the plant or part of the vine suddenly collapses, and within a few days, the stem and leaves turn black and die. Cut off and destroy all the affected parts. Rake up and dispose of fallen foliage. If the clematis was planted 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 vines. This is a disease mainly of large-flowered hybrids. Small-flowered hybrids, the species and their cultivars, are less susceptible to wilt. Therefore, try one of the lovely small-flowered species if there has been trouble with wilt in the past.

Clematis leaf spot can be controlled with foliar sprays of thiophanate methyl and the stem rot controlled with soil drenches of thiophanate methyl. Follow label directions for mixing and use. See Table 1 for products containing thiophanate methyl.

Powdery mildew may occur on plants in areas with poor air circulation. This can be reduced by planting where there is good air movement. When visible, the powdery fungal growth can usually be found on the upper surface of the leaves and tends to begin on lower leaves. As the disease progresses, leaves become dwarfed, curled, and generally distorted. In severe cases, leaves will turn yellow or even dried and brown. Powdery mildew fungi will also infect flowers, causing them to develop abnormally or fail to open.

To help prevent diseases, avoid getting the foliage wet by irrigating at the base of the plant. If powdery mildew is noticed on only a few leaves, simply removing them will help with control. At the end of the growing season, remove fallen leaves, which can serve as a source of further infection later. Fertilize clematis to optimize plant health, but avoid over-fertilization with nitrogen, as it stimulates young, succulent growth, which is more susceptible to infection.

For fungicides to be effective in powdery mildew control, they must be applied as soon as symptoms are noticed. Myclobutanil, propiconazole, tebuconazole, and thiophanate-methyl are fungicides that have foliar systemic properties, and these can be sprayed less often for disease control than required for contact fungicides, such as chlorothalonil, sulfur, or copper-based fungicides. Horticultural oil mixed with potassium bicarbonate can also give good powdery mildew control on ornamentals. When powdery mildew persists and sprays are repeated, it is recommended to rotate (alternate) any systemic fungicides with contact fungicides in order to decrease the chance of fungi developing resistance. Please see Table 1 for fungicides labeled for powdery mildew control on clematis.

Aphids may feed on new growth early in the season. Mites cause a fading of green leaf color, which makes the leaves look dusty or yellowed. Their feeding may result in distorted growth. Heavy infestations can reduce the number and quality of blooms. As they feed, aphids excrete honeydew, a sugary substance that attracts ants and wasps. The honeydew supports the growth of unsightly, dark-colored sooty mold fungi on the leaves.

Aphids can be controlled by sprays with an insecticidal soap. Repeat spray three times at 5- to 7-day intervals. If stronger insecticides are deemed necessary, sprays containing bifenthrin, cyfluthrin, lambda cyhalothrin, permethrin, or pyrethrin will control aphids. Repeat sprays are needed. Soil drenches or granular applications of the systemic insecticide imidacloprid will control aphids and last longer within the plant to prevent future infestations. See Table 2 for products containing these insecticides for use on clematis.

Slugs may attack the foliage of newly planted vines or even feed on the bark of young stems. Control slugs by the nearby placement of slug baits that contain iron phosphate. See Table 2 for available brands of slug baits.

Rabbits and mice may feed on and girdle stems.

However, once well established, most clematis tend to be trouble-free.

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.” They need at least 6 hours of sun to flower best, but in South Carolina they will benefit from some shade during the hot afternoon. Flowers of some red, blue, and bicolored large-flowered hybrids fade if they get too much sun. These should be planted in eastern sunlight exposures or partial shade.

Though the plant’s stems and foliage should be in sun, the roots like a cool, moist environment. The soil can be kept cool and shaded by planting low groundcover plants or perennials that have shallow, noninvasive roots. Alternately, a 2-inch layer of mulch also provides a cool root environment. Most clematis can be grown in South Carolina as long as the plant base and roots are protected from the afternoon 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.

Soil in the planting area should be prepared to a depth of 18 inches deep and 12 to 15 inches wide. Incorporate compost or planting mix 20% by volume in the soil 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. However, these supports must be thin since clematis vines climb by twining the bases of the leaves around a support. They cannot grasp thick branches or heavy trellising. Latticework or trellises can be used if clematis are 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, such as the Armand clematis.

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. A soil test is always the best method for determining the fertilization needs of clematis. For more information on soil testing, see HGIC 1652, Soil Testing. Do not fertilize clematis while it is flowering.

Pruning

Clematis are divided into three groups based on the recommended pruning methods used for each. The pruning method that is used depends mainly on the time of year the plant flowers. If unsure what group the plant is in, then watch it for a year to see when it blooms. Make cuts carefully as the vines will likely be tangled, and dormant vines may appear lifeless.

‘Nellie Moser’ is a large-flowered clematis in group 2.
Barbara H. Smith, ©2019 HGIC, Clemson Extension

Group 1 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 2 Large-Flowered Cultivars: Large-flowered hybrids bloom in mid-June on short stems from the previous season’s growth and often flower 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,’ and ‘Mrs. Cholmondeley’.

Group 3 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, ‘Perle d’Azur’, ‘Royal Velours’, and ‘Duchess of Albany’.

Species & Cultivars

Group 1 Early-Flowering Clematis:

Alpine Clematis (C. alpina) grows 6 to 8 feet tall and blooms in 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. This vine can be cut 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. The cultivars of C. montana var. rubens have flowers with a richer, pastel pink color than the plain species.

Group 2 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 and deep purplish-blue with bright magenta bar. They fade to mauve-blue.
• ‘Ernest Markham’ is an easy to grow clematis that reaches a height of 10 to 15 feet. It has red, magenta, and burgundy hued flowers with yellow anthers.
• ‘General Sikorski’ has lilac to lavender blue 6 to 8 inch blooms. The flowers have a ruffled, wavy texture with yellow anthers. It grows 8 to 10 feet tall.

‘Ernest Markham’ is an easy to grow clematis that reaches a height of 10 to 15 feet.
Barbara H. Smith, ©2019 HGIC, Clemson Extension

‘General Sikorski’ has lilac to lavender blue 6 to 8 inch blooms.
Barbara H. Smith, ©2019 HGIC, Clemson Extension

• ‘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 3.
• ‘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.

‘Henryi’ has large white flowers.
Karen Russ, ©2007 HGIC, Clemson Extension

‘Multi Blue’ has deep purple to blue double flowers.
Barbara H. Smith, ©2019 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. It has a free-flowering habit.
• ‘Marie Boisselot’ grows to 8 to 12 feet and flowers from June to September. Opening flower buds are flushed with lilac-pink, flowers are 8 inches in diameter. This cultivar is a strong grower.
• ‘Mrs. Cholmondeley’ grows up to 20 feet. It blooms from May to October with light lavender blue flowers, which are paler along the midrib. This can also be given group 3 pruning.
• ‘Nelly Moser’ grows up to 8 to 10 feet with flowers from May to June and repeat blooms 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; therefore, provide some shade for this plant.
• ‘Multi Blue’ has deep purple to blue double flowers. It blooms in the late spring to early summer and then again in the fall. It grows 6 to 8 feet tall.
• ‘Niobe’ grows 8 feet tall and flowers from June to September. Its cup-shaped blooms open dark ruby red then turn to bright ruby red with cream stamens. The first flowers are 6 inches in diameter, whereas the later ones are 4 inches in diameter. This is a moderate grower with some flowering throughout the season.
• ‘Perle d’Azur’ grows to 16 feet. This cultivar flowers continuously in early summer to mid-autumn. The blooms are 4 to 6 inches in diameter and are sky blue with green stamens.
• ‘Ramona’ has 6 to 8 inch lavender blue flowers contrasted with red anthers. It grows 8 to ten feet tall.

• ‘Toki’ flowers in the late spring to early summer with single, 6 to 8 inch white blooms that contrast well with yellow anthers. It will bloom again in the late summer to early fall.

‘Niobe’ grows 8 feet tall and flowers from June to September
Barbara H. Smith, ©2019 HGIC, Clemson Extension

Ramona clematis (C. ‘Ramona’) has large, 6 o 8 inch lavender blue flowers with red stamens.
Barbara H. Smith, ©2019 HGIC, Clemson Extension

Toki clematis grows from 4 to 6 feet and has large white flowers.
Barbara H. Smith, ©2019 HGIC, Clemson Extension

Group 3 Late-Flowering Clematis:

Woodbine (C. virginiana) A native to Eastern North America, this clematis is similar to the sweet autumn clematis, but is not invasive. The fragrant, star-shaped flowers bloom on new growth from August to October. It can be pruned back to the ground in the early spring to encourage new growth. It does have the tendency to reseed and also spread by its suckering growth habit; therefore, caution should be taken in choosing the proper site for planting.

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.

Rooguchi Clematis (C. ‘Rooguchi’) A non-vining, multi-stemmed clematis that grows 6 to 8 feet tall and 3 to 4 feet wide. The small, nodding, bell-shaped flowers are deep plum-purple.

Rooguchi clematis (C. ‘Rooguchi’) has purple bell-shaped flowers.
Barbara H. Smith, ©2018 HGIC, Clemson Extension

Rooguchi clematis (C. ‘Rooguchi’) has purple bell-shaped flowers.
Barbara H. Smith, ©2018 HGIC, Clemson Extension

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) The Italian clematis grows 10 to 12 feet and blooms July to September. Its rich, deep purple flowers are 1.5 to 2.5 inches across. This vigorous clematis is tolerant of warm roots and is easy to grow. It originated in southern Europe and western Asia and is adapted to a hot climate.

• ‘Etoile Violette’ has deep violet flowers.
• ‘Alba Luxurians’ has solid white flowers.
• ‘Mme. Julia Correvon’ has wine red flowers.
• ‘Polish Spirit’ has deep purple flowers 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. Its flowers are 4 to 6 inches in diameter and pink with creamy stamens.
• ‘Vyvyan Pennell’ grows up to 8 feet. The 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

Invasive Species

It is not recommended to plant sweet autumn clematis (C. terniflora), as it is a highly invasive vine. It grows vigorously to 30 feet and reseeds freely. Sweet autumn clematis is listed on the South Carolina Exotic Pest Council Invasive Species List as a significant threat.

Sweet autumn clematis (C. ternifolia) is a highly invasive vine.
Barbara H. Smith, ©2018 HGIC, Clemson Extension

Sweet autumn clematis seeds freely.
Barbara H. Smith, ©2018 HGIC, Clemson Extension

Table 1. Fungicides for Disease Control on Clematis.

Table 2. Insecticides for Clematis Insect Pest & Slug Control.

Originally published 10/99