Regional Gardening Reports :: National Gardening Association

In the Garden:
Pacific Northwest
December, 2006
Regional Report

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Even though the scent of a clematis is not powerful, the mass of blooms produced can fill the air with fragrance.

Clematis, the Queen of Vines

The other day a gardening friend informed me that she'd never had any luck with clematis. Either they didn't survive, didn't thrive, didn't flower well, or didn't look good because she pruned too much or too little and probably at the wrong time. And she hated their bare legs and the fact that the flowers appeared only at the top of the vine, way out of sight. Her basic conclusion: "They're more trouble than they're worth."

My own experience has been quite the opposite: these beautiful and versatile vines are easy to grow, provided you take certain steps. I'll show you how, and I'll also suggest a few tried-and-true varieties.

Purchasing Plants
I recommend you purchase a potted plant -- the bigger the better -- at a nursery or garden center. Look for healthy green growth and more than one stem. You can plant in spring, but fall planting works well, too. I plant most of mine in September and October, and some as late as mid-November, and have yet to lose one to late planting.

Site Selection
Clematis are sun-lovers, and for optimum flowering they require at least 4 hours of sun a day. But not all clematis flowers fare well in hot afternoon sun. The flowers of some red or blue hybrids and some bicolors fade badly if exposed to afternoon sun. Give them eastern exposures or lightly filtered sun in the afternoon, and if that's not possible, you might want to try some of the small-flowered hybrids whose colors seem to stand up better in these situations.

Supporting the Vines
Once you've selected a site for your clematis, what kind of support should you provide? There's not much that you can't grow clematis on, as long as you match the ultimate size of the plant with the size of your support. Stone walls and fences make good supports, as do large dead stumps and old sheds. Arbors and pergolas are perfect for the more vigorous varieties. Clematis climb with the aid of their leaf petioles rather than tendrils or aerial rootlets (the modified roots that allow English ivy to climb walls). To encourage a vine to grow vertically, tie the woody stems to the support; the leaf petioles will then twine around and climb right up.

If you want to grow a clematis up the side of your house, lattice and heavy strapping provide good support, as does plastic-coated wire. Whatever kind of support you choose, remember not to plaster it against the wall; allow at least 4 inches of breathing room for both plant and house. I also suggest you choose a trellis that can be detached and laid on the ground when the house needs painting or repair.

Clematis perform best in rich, well-draining soil with a pH close to neutral. I recommend you dig a planting hole 24 inches wide and 18 inches deep to give ample room for root growth.

Before planting, prune the plant back to 12 inches or so. I know this is hard to do, but if you don't, the brittle stem may snap off at the base while you're planting. Besides, you want your plant to branch out at the base and develop multiple stems so you get more flowers.

Plant your clematis deeply, with the crown at least 2 inches below the surface of the soil. If the top of the plant is mowed off or devoured by some marauding animal, there will always be dormant buds below the surface to initiate new growth.

Most clematis thrive in hot weather but their roots prefer a cool, moist environment. The ideal way to keep the roots cool is to shade them by underplanting with a ground cover or with perennials. Lay down a thick layer of organic mulch the first year to allow the clematis to become established. Then surround it with plants that have shallow, noninvasive roots.

Caring for Clematis
Caring for clematis is simple. In the dry season, a weekly, deep watering is a must. As for fertilizer, a yearly application of 5-10-10 sprinkled around the base of the plant is usually sufficient. I always do this after the plants have gone dormant. The nutrients are then available to the roots as growth begins in the spring.

Pests and diseases of clematis are few. Insect pests include earwigs, Japanese beetles, and blister beetles; all can disfigure flowers and foliage but they're mainly just a nuisance. The easiest method of control I've found is to simply hand-pick and destroy the pests. Deer and rodents, on the other hand, have sorely tested my resolve. I have had mixed results with homemade deterrents such as pepper spray and soap bars. Maybe I need a dog with a louder bark?

By far the most serious problem affecting clematis is clematis wilt. This is a fungal disease characterized by the sudden wilting of all or part of a vine, usually when it's in full bud and often during hot and humid weather. All affected parts should be removed promptly and destroyed. Don't despair if the plant is killed back to the ground. It will almost certainly regrow eventually, especially if it was planted deeply. There is no cure for wilt, but a regular soil drench with the fungicide benomyl is an effective preventative. A nonchemical alternative is to grow the small-flowered varieties, which are virtually impervious to wilt.

Pruning Clematis
Pruning is a task that many gardeners dread because they find it so intimidating. In fact, pruning is really very straightforward, and if you make a mistake, it's not terminal for the plant or for you. The flowering season of a clematis determines when and how it should be pruned. There are three basic groups.

Group A: clematis that flower once a year, in very early spring, on old wood (the previous season's growth). These need to be pruned only if growing space is limited. Prune them immediately after they bloom so the new growth has time to make flower buds for the next year. This group includes Clematis montana, C. alpine, C. macropetala, and their cultivars.

Group B: large-flowered hybrids that bloom before the end of June on the previous season's growth, and then flower again on new wood in September. Prune these vines with a light hand in early spring, concentrating primarily on removing dead and weak stems. This clematis group includes doubles, such as 'Duchess of Edinburg', and singles, such as the popular 'Henryi'.

Group C: clematis that flower only on new wood, starting in mid-June (depending upon the variety) and continuing into the fall. These are the easiest clematis to prune. Since the old wood doesn't bear flowers, there's no reason to keep it. Prune last year's stems in early spring to a height of about 12 to 18 inches -- just above a good pair of buds. This encourages new growth to emerge from the base and from below the soil, resulting in a stockier plant with greater flowering capacity. Varieties in this group include sweet autumn clematis (Clematis maximowiczianan), C. viticella and its hybrids, and large-flowered hybrids such as C. x jackmanii and 'Perle d'Azur'.

If you have any doubts as to which group your clematis falls into, just observe it for a year or two, noting when it flowers and whether it flowers on old or new wood. Then prune accordingly.

Foolproof Favorites
The array of large- and small-flowered species and hybrids can be bewildering. Here are a few of my foolproof favorites. They're vigorous, disease resistant, hardy to at least USDA Zone 4, and easy to prune. Best of all, they're beautiful!

'Etoile Violette' (Group C). I prefer this small-flowered Clematis viticella hybrid to the ubiquitous C. x jackmanii. Its 3-inch-wide, dark purple flowers are much richer in color, with a more prominent yellow center and a more distinguished form. 'Etoile Violette' also has a longer bloom season (June to September) and much better foliage. It loves full sun and won't fade a bit. It grows 8 to 12 feet tall and is perhaps the most exuberant bloomer of all the hybrids. You'll love it.

'H. F. Young' (Group B). This is unquestionably my favorite of the large-flowered hybrids. It produces cascades of 6- to 8-inch-wide, Wedgewood-blue flowers set off by creamy white stamens. Although its season is May into June, and September, 'H.F. Young' is seldom out of bloom for me during the summer, especially if I keep it well fed and well watered. A compact grower (8 to 10 feet tall), this plant is always full at the base; I've never had one get leggy.

'Miss Bateman' (Group B). This is a handsome, creamy white, large-flowered hybrid. The 5-inch-wide blooms aren't actually all that large, but they are beautifully shaped, with overlapping sepals and tapered tips. The chocolate-red stamens provide a nice contrast. 'Miss Bateman' is a short vine, growing only 6 feet tall. She flowers very freely in May and June and again in September. Like 'H.F. Young', she is seldom out of bloom if well fed and well watered.

'Comtesse de Bouchard' (Group C). This vigorous and hardy clematis produces masses of 5-inch-wide, soft mauve-pink flowers with creamy stamens on the current year's growth from July to September. It's a nice, full plant, not too big (8 to 12 feet tall), and therefore a good choice for small gardens. 'Comtesse' holds her color well and is a reliable performer.

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