THE WASHINGTON POST – About five years ago, I planted a clematis at the foot of my arbour and proceeded to forget about it.
This is what is required of clematis; you plant it in fairly rich soil, you chop it back, then you let it slumber for at least two years. The gardener’s willful lack of ambition for the vine is rewarded in time. In the second summer, the flowering was scant but pretty amid the roses; in the third summer, it was upstaging the roses; and by the fourth year, it was sensational, forming a bower of violet-purple blossoms – hundreds of them – that persisted through most of the summer.
This lag time is simply about letting the plant develop a robust root system before it turns its attention to top growth. It’s a trait shared with many aerial plants, including grapevines and rambling roses, but the clematis does it with aplomb.
My variety is named Sweet Summer Love, and it stands not just as a symbol of the value of delayed gratification but also of the quiet reinvention of the clematis in recent years.
For more than a century, gardeners have been drawn to large-flowered varieties, the sort that adorn mailboxes with star-like blooms of eye-popping size. In recent years, breeders and growers have developed small-flowered varieties, such as my Sweet Summer Love, which provide more vigour, a longer, later season of bloom, and greater resistance to a disease named clematis wilt.
Early large-flowered varieties, in particular, seem most prone to the disease. There is no malady more deflating to the gardener; one evening you see the vine about to burst forth, and the next morning you are greeted with stems and unopened buds that have collapsed. Not every stem is always afflicted, but it’s enough to ruin the show.
President of the International Clematis Society Jeff Jabco, remains a big fan of large-flowering hybrids, including newer varieties, but he agrees that the clematis novice will find the small-flowered types, particularly those of the species Clematis viticella, more bulletproof.
Viticella varieties of note include Etoile Violette, Betty Corning, Venosa Violacea, Little Butterfly and Burning Love. Some have blooms that are shaped more like a bell than a star, but that adds to the diversity.
I like these small-flowered varieties for two more reasons: You can cut most of them back hard in late winter without fear of getting it wrong (clematis pruning is notoriously convoluted), and I like the colours – deep, saturated reds, plums, blues and purples. Lighter tints are also available, along with that most novel clematis colour, yellow. That would be Clematis tangutica and its varieties, which also have particularly eye-catching, fuzzy seed heads.
Much of the new direction in clematis is being steered by a handful of well-known hybridisers and growers, notably Wim Snoeijer in the Netherlands, Raymond Evison in the British Channel Islands and Szczepan Marczynski (the creator of Sweet Summer Love) in Poland.
Evison and Snoeijer, in particular, have focussed on shorter varieties suited to growing in containers. These potted clematis still benefit from some support, if only three bamboo stakes fashioned into a teepee. Container-grown clematis require frequent watering and feeding in summer, but the pots must drain freely.
Another group getting attention includes low-growing scramblers rather than clinging vines – useful at the top of a wall, in a container or wedged between perennials.
Jabco, who is also Grounds Director and Coordinator of horticulture at Swarthmore College’s Scott Arboretum in Swarthmore, Pennsylvania, conducted a trial of more than 50 clematis varieties at the arboretum and two other public gardens in southeastern Pennsylvania. The top performers were Dutch Sky, with icy blue flowers; Bagatelle, with five-inch blue blooms tinged with mauve; East River, with purple blooms on a five-foot scrambler; Marcelina, with violet blooms; Samaritan Jo, which is compact with blue-white flowers edged with purple; the Countess of Wessex, which is compact and light pink with a darker stripe; and, hurrah, Sweet Summer Love.
The Scott Arboretum also tested 40 Evison varieties developed for container- and small-garden use and listed Cezanne, Juliane, Kingfisher, Parisienne and Sally as top performers. Jabco said he has also been impressed with a lilac-blue large-flowered variety named Laura, a deep purple viticella named Dark Eyes, and another viticella, Solina.
In addition, the clematis society lists recommended varieties by type, though recommendations vary by climate. Varieties of Clematis alpina and macropetala (called Atragene clematis) struggle in hot climates. The classy, early-flowering and vigorous C montana is content in the Mid-Atlantic but not much farther north (too cold) or south (too hot).
The one to avoid is the sweet autumn clematis, which produces large, fragrant bowers of tiny white blossoms in late summer but seeds madly and invades natural areas. An alternative is Clematis virginiana, another big clematis with small white blooms at the back end of summer, but a native species. An easier native clematis to use is C texensis and its cultivars, which have vines up to 10 feet and small red blooms, some tulip-shaped.
Some clematis benefit from being planted deeper than when in the nursery container, but not all. If you’re not sure, keep it at the same level. What is important (and hard for the beginner to do) is to cut back the top growth to 12 inches or so at planting time, so the plant’s initial energy is put into the roots. Clematis like moisture but not wetness, which is why organically enriched soil is good. A light mulch will help keep roots cool, but don’t pile heavy mulches on the stems. Clematis also benefit from feeding, especially the new hybrids that have more flower power. “In general, rose or tomato feeds tend to be pretty good for clematis,” said owner Dan Long of Brushwood Nursery, a clematis specialist in Athens, Greece. If it turns dry, give your clematis a good root-soaking weekly.
Clematis wilt is a specific fungal disease, often associated with large-flowered cultivars that are in areas with inadequate air circulation and sunlight. Fungicides are not practical. The wilt usually doesn’t kill the plant, but it always threatens to return when you least want it to: at blooming time. Cut infected stems to the ground and trash them, along with any plant debris. If your clematis wilts persistently, the best you can do is dig it up and plant it in a more open site, and don’t plant a new clematis in the old site.
Before you do that, though, consider that wilting symptoms may not be a result of the disease, but damage to the stems, which are notoriously brittle. This can be caused by slug feeding or the wind-whipping of vines that are not properly secured. Damage also can be caused by pets or clumsy weeding, Long said. At the very least, keep lawn mowers, string trimmers and leaf blowers away from clematis vines.
Jabco added, “It’s really important to have a very good trellis structure, so these stems aren’t whipping around in the wind.” The vine needs supports that are no larger than the diameter of a pencil, because it tethers itself with its slender leaf stalks, he said.
Most clematis benefit from pruning, which keeps the plant from becoming congested and maintains the floral display at eye level rather than in the treetops. Pruning also allows the removal of damaged and weak stems and provides an opportunity to check and replace ties to supports.
Differing pruning regimes cause undue uncertainty and anxiety. Basically, clematis that bloom early, such as montana, the Atragene and the evergreen C armandii, should not be pruned in late winter to early spring, because they are about to grow and flower. Instead, they can be trimmed back right after they flower. Clematis that bloom from early summer on, including the viticella hybrids, can be cut back hard in March. Cut the stems cleanly just above a pair of healthy buds.
The confusion comes from a third group of clematis, the early large-flowered varieties that are trimmed in late winter, but not cut back hard. Guides suggest leaving some stems around 30 inches, and others longer, around 48 inches. This will promote a longer season of flowering, because these varieties bloom on old and new wood. It also helps generate new growth from the base. Popular varieties in this group include Nelly Moser, Duchess of Edinburgh and Belle of Woking. The clematis society has sought to simplify this by publishing a table of pruning regimes (clematisinternational.com) based on the growth habit of the plant.
The simplest approach is to plant small-flowered summer-blooming hybrids, such as Sweet Summer Love, knowing you can just prune them hard in late winter.
Jabco suggests also cutting them back to 18 to 24 inches right after flowering, allowing them to regrow and flower again in the autumn.
If you’ve run out of arbours, trellises and walls to prop up clematis, there are many other supports: shrubs, hedges, trees and rambling and climbing roses. Just make sure the root competition isn’t too fierce.
“The possibilities are endless as long as you’re willing to have an informal garden,” Long said.
Gardening tip: Late-season perennials, such as asters, perovskia, chrysanthemums, buddleia, caryopteris, persicaria and Joe Pye weed, all benefit from chopping back now by one-third to one-half to promote a bushier habit that will look neater and avoid the need for staking.