In the Garden:
Pacific Northwest
July, 2012
Regional Report

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I'm coaxing this clematis to grow around my front deck, attaching the stems with simple plastic garden ties. When the plant is fully leafed out, you can't see the ties.

Clematis: A Most Spectacular Flowering Vine

I've heard a bevy of complaints about growing clematis from my gardening friends, but I've never experienced any of the problems they report, so it's hard for me to empathize. Instead, I encourage them to try again, following a few simple rules. I'm sure if they do, they'll discover their plants will thrive and bloom beautifully for many years to come.

When you purchase a potted clematis, look for healthy green growth and two or more stems per plant. You can plant in spring or early summer, but fall planting works well, too, so don't be afraid to purchase a potted plant during the summer months.

Selecting the Right Site
For optimal flowering, clematis vines require at least four hours of sun a day, but they can be sensitive to hot afternoon sunshine. I've found an eastern exposure is best, or a site that receives direct morning sun and filtered afternoon shade from a nearby structure, dense hedge, or deciduous tree. Red and blue flowering hybrids and some bicolors will fade if they have to endure hot afternoon sunshine. If you have only a site with full sunshine, try growing white flowered clematis or one of the small-flowered hybrids. These seem to stand up better to hot summer sun.

Planting for Success
Clematis performs best in rich, well-draining soil with a pH close to neutral. I recommend digging the planting hole 24 inches wide and 18 inches deep to give the roots ample room to grow. 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 stems 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 deep, 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.

Clematis vines likes their tops in the sun but their roots in the shade, where they can stay cool and moist. I've found a good way to accomplish this is by underplanting with a ground cover or a low growing shrub. I like to put down a thick layer of organic mulch the first year to allow the clematis to become established, and then surround it with plants that have shallow, noninvasive roots.

Supporting the Vines
Clematis likes to climb, so your plant will need support. I've seen vines growing along stone walls and fences and tumbling over old tree stumps. They look quite happy sprawling in large mounds, but I think they flower best when they're growing upright. Arbors and pergolas make good supports, as do lattices attached to above-ground decks or the side of a house or garage. Clematis vines 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.

On-going Care
Caring for clematis is simple. If the weather is dry, 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.

There are a few insect pests that disfigure flowers and foliage when they feed, but they're mainly just a nuisance. I think the easiest approach is simply to hand-pick and destroy them.

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 plant parts should be removed promptly and destroyed. Clematis wilt kills the stems but doesn't affect the roots, so even if the top of the plant is killed back to the ground, it will eventually regrow. There is no cure for wilt, but some gardeners apply a soil drench with the fungicide benomyl in early spring as a preventative measure. Because I choose not to use systemic fungicides in my garden, and because clematis wilt occurs rarely in my gardening region, I'd rather take my chances and avoid using unneeded chemicals. 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 usually terminal for the plant. The flowering season of your clematis will determine when and how it should be pruned. Clematis are categorized into three basic pruning 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 terniflora), 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.

I hope these suggestions enable you to successfully grow clematis. If so, you'll be the envy of your gardening friends.

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