The Queen of Climbers

Whether you pronounce it CLEM-a-tis or cle-MAT-is, these pretty plants climb and shine.

By Mary Lynn Bruny

During a garden tour years ago, I found myself in the magical backyard of an elderly lady. “Oh, my!” I gushed to her, “Your clematis vines are wonderful!” She looked at me with disdain and said icily, “It’s ‘CLEM-a-tis,’ dear, not ‘cle-MAT-is,’” imitating my nasal Ohio accent.

    But according to Linda Beutler, president of the International Clematis Society, curator of the Rogerson Clematis Collection outside Portland, Ore., and author of Gardening with Clematis: Design and Cultivation (Timber Press 2004), that old gardener was wrong. “Either pronunciation is acceptable,” Beutler states. That being said, Beutler and other serious gardeners pronounce it “CLEM-a-tis.”

No matter what you call the queen of climbers, it’s hard to resist adding a few of these beauties to your garden, and spring is the best time of year to do so. Most folks are familiar with the dark-purple ‘Jackmanii’ variety growing on countless mailboxes, but there are hundreds of types of the mainly deciduous vines (not to be confused with herbaceous perennial clematis) that range from 3- to 20-feet tall and come in just about every color but orange.

The standard clematis flower form is a large, flat blossom with six or seven sepals (petals), measuring from 3- to a dramatic 11-inches across. There are also wonderful cultivars with puffy double blooms and others with graceful bells, teeny stars and windsock shapes. Flowers are followed by bursts of attractive fluffy seed clusters.

Natural companions to roses and herbaceous perennials, clematises add color, texture and vertical interest to a garden. Most clematis vines are not difficult to grow, but they do have specific requirements to help them thrive and produce spectacular blooms. Once established, they can live for decades, some up to 50 years.

Choosing a Vine

It’s easy to have your head turned by the pretty flowers of a blooming clematis at the garden center. But before making a purchase, you’ll want to consider a few factors in addition to vine size, flower form, color and bloom period. Some cultivars require very simple pruning, while others need more attention. Although most clematises are fairly easy to grow, some cultivars are more vigorous growers with longer bloom times.

When buying a plant, look for multiple stems with healthy foliage and roots coming out of the pot’s drainage holes, rather than a spindly plant with lots of flowers or buds. It takes several years for a clematis vine to mature, so if you buy a bare-root or young plant you’ll need to baby it and wait a couple of years for blooms.

“The hardest thing is when you buy them at a garden center like Home Depot and they come in little square boxes with hardly any roots and one stem coming out of the top. That is just a touch-and-go time for them,” says Thad Napp, owner of Napp Landscape Services in Hygiene. “Nurseries sell older plants in larger containers so you’ll get a much more established plant and have a lot better success with it. You’ll pay more, but you’ll be happier in the long run.”

If you buy bare-root or very young plants, Beutler suggests putting them in a 1-gallon pot and letting them grow until roots exit the drainage holes before planting them. However, there are planting situations in which only small or bare-root clematises will work, such as in between flagstone pavers on a patio. In this circumstance, make sure to keep the vine moist for the first season and apply root stimulator.

How to Plant

Although a few clematises grow in partial shade, such as ‘Nelly Moser’, most require six hours or more of sun each day. Plants are happiest with “feet in the shade and head in the sun.” In other words, the roots like to be shaded while the foliage gets the sun. Plant vines behind a small bush or other plants, or use hardscape materials to shade the roots.

“I use 1- or 2-inch-thick flagstone pieces and put a 3-foot diameter grouping at the base of the plant to keep the root systems cool,” says horticulturist and public speaker Merle Moore, former executive director of Denver Botanic Gardens. He advises against using anything thicker, or it will conduct heat.

Like many plants in Colorado, clematises grow best when planted in spring. They prefer well-drained, rich soil. But before planting, Beutler advises cutting the foliage back by half—something many gardeners are loath to do. “You do this to reduce transplant shock,” she explains.

“No matter how careful you are, you damage feeder roots when you transplant. The plant doesn’t have the ability to support top growth when its roots are damaged. And then the top growth will collapse and you’ll feel like a bad parent.” If the plant is flowering when you buy it, wait until after it’s finished to cut it back and plant.

For large-flowered hybrids, dig a hole twice as deep as your pot; these clematises have long roots that need room to grow. Plant the hybrids 2- to 3-inches deeper than where they sit in the pot. This allows buried nodes to make new growth.

For all other clematis types, plant them level with where they sit in the pot. Be as gentle as possible when planting your vine; the roots, crown and emerging vines are all fragile. Backfill the hole with rich soil mixed with organic compost, and then cover with mulch. For the first season, water as needed—about twice a week—to keep soil moist and to get the plant well established. Don’t overwater; clematis roots can’t handle being waterlogged. After you get a plant through its first year, it will usually continue to do well. But don’t pull it out if it appears to die; it may surprise you by popping back up next spring.

Training Clematis

Give your new vine something to grow on, like a trellis, fence or arbor. A handy product at local nurseries is a downspout trellis—a tall, curved, green, plastic-coated grate that fits over a downspout. Or join two downspout trellises to cover a pole. A born climber, clematis will start looking for something to wrap its leaf stem around, a rather fascinating thing to observe. Keep in mind anything over a half-inch is too wide for a leaf stem to twist around. The more things there are to grab onto, the better for the vine.

If you have a trellis with big, wide-open gaps, add twine, fishing line or wire to the gap areas, or simply back the trellis with chicken wire. As the vine grows up the trellis, guide stems to open areas to provide wider coverage and flower display. Secure stems with reusable green Velcro gardening tape, available at most nurseries.

Once the clematis has a well-established root system, it can be transplanted fairly easily. Make sure your hole is ready before transplanting, and cut back and plant the same way you would for a new vine.

Fertilizing Correctly

Well-established clematises put out an amazing amount of foliage and flowers each season. To keep a vine healthy, apply a good organic fertilizer, such as those with a 5-10-10 or 4-6-2 combination (the numbers represent the percentages of nitrogen, phosphorous and potassium, respectively). “Clematises generally are heavy feeders. If you don’t fertilize you’ll get fewer blooms and very lanky growth. It will be spindly and not very strong,” Beutler says. “But don’t use a lot of nitrogen because you want flowers, not leaves.” Any fertilizer mixture for roses also works well for clematises. If potted vines have yellowing leaves, your plant has a magnesium deficiency; use a tomato fertilizer.

In spring, fertilize before the plant blooms, but stop when the flower buds are maturing. “If you fertilize after this point, you’ll overtax the vascular system and the whole plant may collapse,” Beutler says. “It’s pretty dramatic and scary for a gardener to see this happen when they think they’re helping the plant. Often people think the plant has a disease, but basically they’re poisoning it.” If this happens, cut back the collapsed part, water well and the vine should recover.

After the vine finishes its initial bloom, fertilize monthly during the growing season, stopping again if it re-blooms.

Pruning Tips

Pruning helps clematises achieve large amounts of flowers on a nicely shaped vine that’s controlled in size. Pruning may seem intimidating, and gardeners are often overly cautious about it, but it’s actually fairly easy. Established clematises are tough, rapid growers—and forgiving, so you really can’t go wrong. If you can’t get to pruning one year, there’s always the next.

Clematises are divided into three basic “pruning groups.” If you know your vine’s species or cultivar, you can identify its pruning group online. If you don’t, observe when it blooms and the flowers’ attributes, then reference the “Clematis for Beginners” section on www.clematisinternational.com for photos and descriptions. If you prune at the wrong time for a given vine, you risk cutting off future flowers. When all else fails and you can’t identify a vine, simply prune it after its initial bloom.

If you have clematises from different pruning groups, you’ll need to keep track of this. Some gardeners tie ribbons or tags to trellises or stick plant identifiers in the ground; others rely on garden maps.

Pruning Group 1:  Spring Bloomers

Clematises in this group, such as alpina and macropetala clematises, bloom in spring on old wood from the previous season. These vines do best in cooler temperatures, such as in the mountains. Although it’s nice to have a spring bloomer, Colorado’s late-spring snowstorms can freeze their buds.

“You can help avoid this by planting them where they get shade in early spring to delay their bloom period,” Moore says. This group needs only the barest pruning after its initial bloom period: Remove dead wood and shape or cut to manage size. They’re more likely to re-bloom if you fertilize after the first flowering.

Pruning Group 2:  Early-Summer Bloomers

This group contains the very showy, large-flowered hybrids that put on a spectacular display in early summer on vines that grow 10 feet tall or less. “Flowers measuring 10 inches across are not uncommon for certain varieties. If flower size matters, this is the group you want to grow,” Beutler says.

These clematises are considered the most demanding; they need rich soil and regular watering and fertilizing. The flowers grow on old wood from the previous summer with a second flowering on the new season’s growth. Pruning is done in the spring, about the same time as roses, and there are two options.

The first is to cut the entire plant back by a third or half. “You start at the top and follow each cane back until you see really fat, new buds. And you cut back to that point, about half an inch above that new bud,” Beutler says. “I look at a whole plant and judge it. If it’s gotten really tangled, I’ll be more ruthless and take it back by half. The more you prune, the more flowers you get.” After the initial bloom, you can prune again as desired. Fertilize again to promote a second bloom. This method is preferred if you want to keep some woody growth and height on a trellis or arbor, and prefer an earlier bloom with the possibility of a second flowering.

The second option is to cut the entire vine down to 12 inches in spring, leaving two sets of leaf buds per stem. “If you do this, the clematis will replenish its whole height during the season, but bloom later,” Beutler says. If you also grow Pruning Group 3 clematises, it keeps things simple, as they require the same method.

Pruning Group 3:  Summer & Fall Bloomers

This group contains late summer/early fall blooming vines, including large-flowered hybrids as well as several species groups such as viticellas, texensis and tanguticas. “These have smaller flowers, not quite as flashy as the large-flowered hybrids, but they’re very sophisticated, charming and vigorous. When you have them in your garden you love them,” says Panayoti Kelaidis, senior curator and director of outreach at Denver Botanic Gardens.

Moore highly recommends cultivars from the viticella group as they’re durable, come in a wide range of colors and flower forms, and grow at high altitudes. Best of all, they bloom profusely from early June to frost. (For a good online selection, see www.clemastisnursery.com.)

Some vines in Pruning Group 3 are overly vigorous: “There are some that once established are totally indestructible. They self-sow and pop up all over,” Kelaidis says. “If you plant the white-flowered ligusticifolia, stand back—it will take over! But it has a more refined cousin, the popular ‘Sweet Autumn’.”

Pruning Group 3 vines flower mainly on new growth. “Hard” prune all stems to 12 inches from the ground in late fall/early winter, after a freeze, or in early spring, leaving two sets of leaf buds per stem. Napp advises spring pruning due to winter dieback on plants. But if you prefer a tidy garden, follow Moore’s practice: “In the late fall or early winter after a frost, when the foliage dies back, I cut mine to 3 feet. I tie the stems together to help protect the crown of the plant and let snow accumulate to insulate it from winter winds. Then in spring I cut it down again. So it’s an easy cleanup,” he says.

If you don’t prune plants in this group, you’ll end up with long, bare woody “legs” devoid of foliage or blooms.

Don’t pull out old tangled clematises in any pruning groups that don’t seem to bloom; they most likely can be revived. Cut back all growth in early spring to 12 inches, water and fertilize well, and the vine should rejuvenate within the season.

Once you understand the basic pruning principles, you can alter your practices to meet your gardening goals. For instance, if you want a ‘Jackmanii’ (Pruning Group 3) to grow to the second story of your house, it will never reach there if you cut it back to 12 inches each spring. Instead, knowing it will grow about 10 feet a year, let it grow until it’s where you’d like it.

Conversely, for Pruning Group 2, the more you cut back these plants, the more you delay the bloom period. “This gives you a chance to manipulate the plant combinations and the flower combinations in your garden,” Beutler says.

My own pruning practices are a bit inconsistent, despite the fact that I’ve grown several-dozen spectacular clematises and should know better. Yet they all bloom profusely and are showstoppers in my garden, so why change now? What I’m really working on is trying to call my vines “CLEM-a-tis!”