Clematis (Clematis spp.) is the classic climbing perennial vine of the border, grown for its abundance of showy flowers rather than foliage or fruit. Unlike vines that cling with tendrils or adhesive holdfasts, clematis climbs by wrapping its leaf stems around whatever it can reach, so it needs a trellis, arbor, fence, or similar support from the start rather than a bare wall. Bloom timing depends heavily on which type you're growing: many clematis flower in late spring to early summer, while others repeat through the season or save their main show for later summer. The large-flowered hybrids sold at most nurseries are the most commonly grown type in home gardens, prized for flowers that can span several inches across in shades of purple, pink, red, and white. Give it the right support, the right light, and a little attention to its roots, and clematis rewards you with years of reliable flowering in the same spot.
Sowing and planting
Clematis is planted as a potted vine rather than grown from seed in almost every home garden. Named large-flowered hybrids are propagated from cuttings to keep their characteristics true, and seed-grown plants, where seed is even an option, can take years to reach flowering size. Set up the support structure, whether a trellis, arbor, or section of fence, before or at the same time as planting, since clematis climbs by wrapping its leaf stems around whatever is nearby and needs something to grab onto almost immediately.
Plant in spring after the danger of frost has passed, or in early fall to let roots establish before winter. Dig the planting hole slightly deeper than the pot and set the plant so that a few inches of stem sit below the final soil level, deeper than it was growing in its nursery container. This unusual planting depth is deliberate: if clematis wilt strikes the top growth later on, having buds buried below soil level gives the plant a much better chance of resprouting from underground rather than dying outright. Space plants 24 inches (60 cm) apart, positioning each one within a few inches of its support so the new growth doesn't have to search far to find something to climb. Water thoroughly after planting.
Follow the well-known rule of thumb for clematis: cool roots, warm top. The vine wants its leaves and flowers reaching up into full sun, but its roots dislike being hot and exposed. Shade the base of the plant with a few inches of mulch, a flat stone laid over the root zone, or low companion plants growing in front of it, while letting the top growth climb freely into the light.
Growing on
Water regularly, especially during the first year while the root system is establishing, and keep the mulch or root-shading cover topped up through summer so the base of the plant never bakes in direct sun. Clematis flowers best with consistent moisture and a yearly application of a balanced fertilizer in spring; established vines appreciate the feed but don't need heavy, frequent doses.
Young vines often need help finding their support at first. Loosely tie the earliest new shoots to the trellis or fence until they're established enough to wrap their own leaf stems around it; after that, the plant takes over the climbing on its own. Keep an eye on vigorous growth early in the season to make sure it's climbing where you want it rather than flopping into nearby plants.
Pruning is the one part of growing clematis that trips people up, because the right approach depends entirely on which of the three general pruning groups a particular variety falls into, and those groups differ by whether the plant flowers on old wood, new wood, or both. Vines that bloom only on growth made the previous year need little more than light shaping right after flowering, since cutting them back hard would remove the wood that was about to bloom. Vines that flower on old wood but also produce a second flush on new growth are usually pruned lightly in late winter or early spring, cutting back to a strong, healthy pair of buds rather than removing large amounts of growth. Vines that bloom only on the current season's new growth, typically later in summer, tolerate and often benefit from a hard cutback in late winter, down to a foot or so from the ground, since all the coming season's flowers will form on growth that hasn't emerged yet. Because getting this wrong can cost you an entire season's flowers, it's worth checking which group your specific cultivar belongs to before picking up the pruners, rather than applying the same cut to every clematis in the garden.
Harvesting
Large-flowered clematis blooms can be cut for a short indoor arrangement, though the stems don't hold up as well in a vase as many other cut flowers, so most gardeners leave the bulk of the flowers on the vine to enjoy outdoors and cut only a few stems at a time for the table. Cut in the morning while the flower is freshly open, and recut the stem end before placing it in water.
Deadheading spent blooms keeps the vine looking tidy and, on repeat-flowering types, can encourage further flushes of bloom through the season. Take care with deadheading on early, old-wood bloomers: removing spent flowers is fine, but avoid cutting back into the stem itself outside the plant's proper pruning window, since that wood is what next year's flowers will come from. On the later, new-wood bloomers, deadheading is more forgiving, since the plant is simply building toward next year's hard cutback regardless.
Problems and pests
Sudden blackening and collapse of stems
Clematis wilt causes healthy-looking stems to blacken and collapse within days, usually on young plants or large-flowered hybrids. It's a fungal problem that affects the stem rather than the roots, which is why planting with several inches of stem buried below soil level matters so much: buried buds below the infection point can often resprout even after the top growth dies back. Cut affected stems down to healthy tissue or to the ground and discard them; don't compost diseased material.
Grayish-white coating on leaves
Powdery mildew shows up as a dusty gray-white film on leaves, especially in humid weather or when air circulation around the vine is poor. Space plants properly, avoid wetting the foliage when watering, and remove heavily affected leaves; established vines usually tolerate a mild case without serious harm.
Emerging shoots chewed or missing in spring
Slugs and snails target the soft new shoots as clematis breaks dormancy, sometimes severing growth right at ground level before it has a chance to climb. Clear debris from around the base in early spring and consider a barrier or bait around new growth until shoots have toughened up.
Clusters of small insects on buds and new growth
Aphids gather on tender new shoots and unopened flower buds, sometimes distorting growth or leaving behind a sticky residue. A strong spray of water usually knocks colonies off without needing further treatment.
Sparse flowering or scorched leaves in a hot, exposed spot
When the root zone is left bare and exposed to direct sun, clematis often responds with reduced flowering or leaves that look scorched at the edges, even if the top growth is otherwise healthy. This is almost always a case of the roots overheating rather than a pest or disease. Add mulch, a shading stone, or low plants in front of the base to keep the roots cool while the top growth stays in full sun.
Varieties worth growing
- Jackmanii – A classic, vigorous large-flowered hybrid with deep purple blooms, reliably easy and widely available.
- Nelly Moser – Pale pink flowers with a darker carmine stripe down each petal, among the most recognizable clematis varieties.
- Henryi – Large, creamy-white flowers on a vigorous vine, a dependable choice for covering an arbor or fence.
- The President – Rich purple-blue flowers with a silvery reverse, flowering over a long stretch of the season.
- Niobe – Deep velvety red flowers with bright yellow centers, a strong contrast plant against lighter-colored neighbors.
- Sweet Autumn Clematis – A vigorous species type covered in masses of small, fragrant white flowers in late summer into fall, useful for quickly covering a large structure.