Clematis — Queen of the Vines

• By Pat Chadwick
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• May 2016-Vol.2 No.5
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• 3 Comments

Gardeners are always searching for plants to provide that “wow” factor in the landscape.   For some of us, clematis is the “holy grail” of ornamental plants.  Few plants elicit as many oohs and aahs as a clematis in full bloom covering an arbor or stone wall.  Even the butterflies, bees, and hummingbirds are as attracted to clematis as we humans.  One of the most spectacular of the flowering vines, clematis enjoys a long-standing and justly deserved reputation as the “queen of the vines.”

Sources vary on the statistics, but it’s safe to say that the clematis genus consists of at least 250 species and more than 2,500 (mainly large-flowered) cultivars.   A member of the Ranunculaceae family, which includes aconites, anemones, buttercups, paeonies, and hellebores, the clematis genus may be found in most countries throughout the temperate regions of the northern hemisphere and, to some extent, the southern hemisphere.    Most clematis varieties are woody, deciduous vines that are hardy to USDA zones 3 or 4.    A few species, such as C. armandii, are evergreen and tend not to be as hardy as their deciduous relatives.    A few selections are bush type rather than vines.

Clematis vines vary considerably in size and color.  Most large-flowered hybrids range from 8 to 12 feet tall, while some of the small, herbaceous species grow a mere 2 to 5 feet. Vigorous species, such as sweet autumn clematis (C. terniflora) and anemone clematis (C. montana), can grow 20 to 30 feet long. Clematis colors range from pure white to deepest purple with shades of pink, lavender, blue, violet, yellow, and red, as well as bi-colors.

During a single growing season, a large-flowered hybrid may have a hundred or more star- or saucer-shaped blossoms ranging in size from 4 to 10 inches in diameter. The flowers may be single, double, or semi-double. The urn-or bell-shaped blossoms on some of the smaller or native species tend to be much daintier in appearance.     Bloom time may run from spring into autumn, depending on the selection.   The feathery or fluffy-looking seed heads that follow the blossoms continue to lend interest to the garden for the remainder of the growing season.

Clematis hybrid ‘Betty Corning’

Of the approximately three dozen North American clematis species, 11 are native to Virginia, according to both Flora of Virginia and the United States Department of Agriculture plant database.  C. viorna and C. crispa are two particularly charming native species.  They have diminutive bell-shaped flowers that range in color from pink to violet purple.  C. texensis, which is native to Texas, is represented by ‘Duchess of Albany’ and ‘Princess Diana,’ both of which sport 2 to 3 inch tulip-shaped pink to reddish-pink flowers.  Because clematis has been widely hybridized since the 1800s, many crosses exist between North American species and their non-native counterparts. For example, ‘Betty Corning,’ a well-known and cherished award-winning hybrid introduced in 1932, is a cross between C. crispa and C. viticella, a native of southern Europe.

Clematis virginiana

Of the native clematis species, C. virginiana is perhaps one of the most widely distributed.  Also known as virgin’s bower or devil’s darning needles, this fall-blooming species is native to the entire eastern half of North America.  Do not confuse this plant with C. terniflora (sweet autumn clematis), a non-native species from Asia. Unlike the vast majority of clematis species, which are generally well behaved, both C. virginiana and C. terniflora are rampant growers and aggressive self-seeders.  Both produce clouds of 1 inch wide white blossoms that give way to attractive, plume-like seed heads.  To distinguish the two, look at the foliage.  C. virginiana has toothed leaves that are trifoliate (3 leaflets).  C. terniflora (which is sometimes sold under the name C. paniculata) has slightly rounded simple leaves with smooth margins.   If you grow either C. virginiana or C. terniflora, cut them back hard in autumn immediately after flowering so that they do not have a chance to set seed.

CULTIVATION AND MAINTENANCE

Clematis has a reputation for being difficult to grow.  Basically, there are several reasons for this perception:  (1) Since the majority of clematis species are vines, some training onto supports is involved initially.  (2)  It takes 2 or 3 years for a clematis to become mature enough to produce the magnificent displays for which it is renowned.  (3)  Most clematis need to be pruned yearly and there’s a lot of confusion about when and how to prune.   If you’re looking for instant gratification, perhaps an annual vine, such as morning glory, hyacinth bean, or moon flower, might be more to your liking.  Otherwise, just be patient.  Once your clematis is established, it is generally no more difficult than any other ornamental plant to grow and maintain.

Cultural Requirements:

• Soil:  Clematis thrives best in moisture-retentive but well-drained soil.
• Light:  Most of the climbing and shrub species will thrive in either full sun or partial shade.  Herbaceous species do best in full sun.
• Water:   Water regularly during periods of dry weather in the first few seasons after planting.

Planting:

• Dig the planting hole close enough to a support so that the vine can be easily trained onto it.
• For large-flowered species and cultivars that bloom in spring, plant the crown 2 to 3 inches deeper in the soil than it was in the pot. This encourages shoots to grow from below the soil level and results in a bushier plant.  Also, deeper planting will help ensure the plant’s survival in the event it becomes infected by clematis wilt (more on that below).
• Plant the crown of herbaceous and evergreen species at soil level.

Training:

• Provide a support such as a trellis, arbor, post, mesh, or tuteur for the clematis to twine around.  Many species of clematis have tendrils, which are thin modified stems or leaves that twist into coils. The tendrils not only wrap around the support but also wrap around each other or any nearby plant.
• A newly planted clematis may initially need to be tied to the support.  Spread the shoots as wide as possible on the trellis to give good coverage.  Otherwise, the plant may grow in a concentrated narrow column up the trellis.

HOW TO PRUNE CLEMATIS

Initial Pruning Guidelines:

If left unpruned, a young, newly-planted clematis may produce a few long single stems with flowers only at the tips of each stem.  To encourage multiple stems and a fuller habit, prune newly planted clematis vines the first spring after they were planted to about 12 inches above the soil level. This can be done in February or March.  Be sure to cut each stem just above a bud.   Once the stems start to grow in the spring and summer, the new growth should be spread out so that it is spaced evenly on the support and tied in place.   Pinching out developing young shoots once or twice will promote further branching.

General Pruning Guidelines:

Clematis vines need to be pruned regularly.  That’s a fact of life.  Pruning encourages strong growth and flowering and keeps growth in check.  If left unpruned, a clematis can become a mass of tangled stems with little foliage near the base and all flowers concentrated on the tips of stems.   For pruning purposes, the vines are grouped into three categories and that’s where the confusion arises.    If you can’t remember which group your clematis fits into, here’s a hint:  it depends on what time of year the plant blooms.  For example:

• Group 1:  Blooms in mid to late spring.  Prune immediately after flowering in mid to late spring. This group blooms in the spring on the previous year’s growth.    Once pruned, the new shoots will develop buds for next year’s flowers.   Slower-growing varieties may not require much, if any, pruning.  The less you prune, the earlier next year’s blossoms will appear.  So be judicious in deciding how far back to prune.
  

  Clematis alpina ‘Tage Lundell’

   

  Vigorous or fast-growing varieties may need to be cut back more severely in order to contain their size.  If you have a very old group 1 clematis with woody stems, avoid cutting down into the old wood because it may be reluctant to set buds in time for the next growing season.  Clematis species belonging to this group include C. alpina, C. armandii, C. macropetala, and C. montana.

• Group 2:  Blooms twice:  In late spring/early summer and again in late summer.   Prune in late winter and again after the first flush of blossoms in spring or early summer. This group consists of many of the large-flowered hybrids and is the trickiest group to prune because the plants bloom twice during the growing season. In general, the spring blossoms occur on last season’s wood and the summer blossoms occur on new shoots.  The goal of pruning this group is twofold:  (1) retain a healthy framework of old wood and (2) stimulate new growth in order to maximize flowering throughout the growing season.  Timing is everything.
  

  Clematis ‘Nelly Moser’

  One approach is to thin out some of the stems in late winter and the rest after the first flush of blossoms.  Make all cuts above healthy new buds.  If this sounds like too much trouble, another approach is to prune the entire plant back by half or more every 2 or 3 years.  In the first year after rejuvenation pruning, the plant will only flower once.  Some plant selections in this group include: C. lanuginose, C. florida, and large-flowered hybrids such as ‘Nelly Moser’,  ‘Miss Bateman’,  ‘Duchess of Edinburgh’, and ‘Mrs. Cholmondeley’ among others.

• Group 3:  Blooms in late summer/early fall.   Prune in late winter. This is the easiest group to prune.   Group 3 clematis vines flower in late summer or in fall on new growth that was produced that season. They send forth new growth from the base each year and can therefore be cut back hard on a regular basis. Simply cut the vines back to about 1 foot from the ground.  If left unpruned, the members of this group will continue growing from where the growth ended the previous season.  This will cause the plant to become top heavy.  Moreover, flowering will occur at the tips of each stem, leaving a bare base.  Representative plant selections in this group include: C. viticella, C. x jackmanii, C. integrifolia, and C. terniflora.
  

  Clematis viticella ‘Rubra’

If you’re still confused about pruning, don’t worry about it.  Even if you don’t prune correctly, clematis is very forgiving.  At worst, you’ll only lose one season of blossoms.

CLEMATIS PESTS AND DISEASES

Most clematis are trouble-free once they become established in the landscape.  However, they may periodically experience damage from several typical garden pests such as aphids, earwigs, whiteflies, red spider mites, slugs and snails.    Deer don’t normally bother clematis, but rabbits may nibble on the tender new shoots as they leaf out in the spring.

Clematis is susceptible to two fungal diseases:  powdery mildew and clematis wilt.  Powdery mildew occurs most often on plants that are planted in areas with poor air circulation.  Clematis wilt is a more serious disease that manifests itself by the sudden collapse of the vine or some portion of it. In general, this happens just about the time the plant is ready to bloom.  Within a few days after collapse, the stem and leaves will turn black and die.  To solve the problem, cut diseased stems off just below ground level and destroy all affected parts of the plant. The vine will usually grow back from the base the following year if it was planted with two buds below ground.   This disease mainly affects large-flowered hybrids.  Small-flowered species and their cultivars are less susceptible.  Plants in their first year of growth seem to be more susceptible to clematis wilt than established specimens.

PROPAGATION

Clematis may be propagated in one of several ways:

• Stem cuttings, which may be taken from spring to late summer
• Layering, which may be done from late winter to spring
• Seed.  While hybrids will not come true from seed, species clematis will.  Sow the seed in pots in the fall and cover with a fine layer of compost and grit. Store the pots in a cold frame or unheated greenhouse until the following spring, at which time the seeds should germinate.

USES IN THE ORNAMENTAL GARDEN

A display of a single mass of clematis blossoms is sure to give you the “WOW” factor you’re going for in the ornamental garden.  Some suggested ways to incorporate this beautiful plant in your landscape include the following:

• Train the vine onto a well-placed trellis, arbor or other vertical structure in the landscape so that the vine can be the star of the horticultural show.
• Weave the vine up and through nearby shrubs or trees if you don’t want to bother training the plant onto a support structure.  Roses and clematis are a classic combination.
• Grow one or more along a low fence to camouflage trash cans or HVAC equipment.
• Plant one of the more compact selections at the base of a mailbox post.  Avoid using the long vining types for this purpose as they will grow too large for the mailbox.
• Let the bush type species sprawl as a ground cover.
• Plant as a backdrop to lower growing annuals and perennials.
• Plant at the base of a fence and let the vine scramble up and over the supports to break up the long expanse.

SOURCES

A-Z Encyclopedia of Garden Plants (The American Horticultural Society, 2008).

Flora of Virginia (Weakley, Alan S.; Ludwig, J. Christopher; and Townsend, John F., 2012).

Native Plants of the Southeast (Mellenchamp, Larry, 2014).

United Stated Department of Agriculture Natural Resources Conservation Service Plants Database website, plants.usda.gov