How to Grow Clematis

Heads in the sun, feet in the shade

The old rule for clematis is still the best one. The vine wants at least six hours of direct sun to flower well, and the roots want to stay cool and moist. Shade the root zone with 2 to 3 inches of mulch, or with low perennials or groundcovers planted around the base. In hot-summer areas, including most of the South, Clemson and NC State recommend afternoon shade. Some red, blue and bicolored large-flowered hybrids also fade in strong sun and do better on an east-facing site.

Pick a spot with good air movement but some shelter from strong wind, and avoid wet ground.

Soil

Clematis like rich, well-drained soil. Clemson prepares a planting area about 18 inches deep and 12 to 15 inches wide and mixes in compost at about 20 percent by volume. Sources differ on pH: Iowa State recommends slightly acid to neutral soil, while NC State suggests neutral to slightly alkaline. In practice, soil close to neutral suits most clematis.

How deep to plant clematis

Clematis are planted deeper than most perennials, with the crown below the soil surface. Buried buds let the vine send up new shoots if the top is damaged, mowed off or killed by clematis wilt. Sources differ on how deep: Iowa State and Nebraska Extension say about 1 inch, Clemson 1 to 2 inches, and a UC Master Gardener handout from California 4 to 6 inches. One to 2 inches is a sound middle course.

1. Dig the hole and amend the soil as above.
2. Set the plant so the crown sits 1 to 2 inches below grade. Straighten crowded roots.
3. Backfill, water well and mulch with 2 to 3 inches of wood chips or shredded bark, kept just off the stems.
4. Cut the stems back to about 12 inches. Both Iowa State and Clemson do this to encourage branching and to keep stems from breaking.

Clematis do not like root disturbance, which is why they are nearly always sold in containers. Early spring is the best planting time. See when to plant clematis for spring and fall timing.

Supports

Vining clematis climb by wrapping their leaf stalks around a support, so the support must be thin: wire, string, netting, thin lattice or the twigs of a shrub. They cannot grip thick posts or heavy beams. Iowa State suggests planting 1 to 2 feet from the support and guiding the young shoots onto it. Clematis can also scramble through shrubs, over stumps or up small trees.

Watering and feeding

Give clematis at least an inch of water a week, as a deep weekly soak in dry weather. Water at the base rather than over the leaves to limit disease.

Feed in spring with a balanced, low-analysis fertilizer such as 10-10-10 or 5-10-5. Do not fertilize while the vine is in bloom, and do not overdo nitrogen, which gives lots of leaves and few flowers.

How to prune clematis by group

Pruning is not essential, but it keeps vines tidy and flowering low on the plant instead of only at the top. Pruning the wrong way at the wrong time is a common reason for few flowers.

Group 1 (early spring bloomers on old wood). These flower in spring from buds formed the year before. Prune only after flowering, and only lightly to shape or remove dead stems. Clemson’s deadline is the end of July.

Group 2 (large-flowered repeat bloomers). These bloom in late spring or early summer on last year’s stems, then again in late summer on new growth. In late winter or early spring, remove dead and weak stems and cut the rest back to the top pair of plump, green buds. Keep it light, or you lose the first flush.

Group 3 (summer and fall bloomers on new wood). These flower on the current year’s growth. Cut them back hard in late winter or early spring, before new growth starts. Iowa State cuts to 6 to 12 inches above the ground, and Clemson to about 2 to 3 feet.

Common problems

• Clematis wilt: a fungal disease that collapses a stem within days, mostly on large-flowered hybrids in their first years. Cut affected stems below the damage or at ground level and clear away fallen leaves. Deep-planted vines usually regrow from the base. Small-flowered species are less susceptible.
• Slugs: eat young shoots and buds. Iron phosphate baits help.
• Aphids, mites and earwigs: usually minor. Insecticidal soap controls aphids.
• Powdery mildew: improve air flow and remove affected leaves.
• Rabbits, mice and deer: may chew or girdle stems. Cage new plants if rabbits are a problem.
• No flowers: too little sun, wrong pruning, too much nitrogen, winter dieback on group 1 or 2 vines, or a young plant that is still settling in.

Choosing clematis for your region

In the upper Midwest, Iowa State finds group 3 vines the most reliable because they bloom on new growth, so winter dieback does not cost the flowers. Its suggestions for Iowa include ‘Jackmanii’, ‘Ernest Markham’, ‘Hagley Hybrid’ and ‘Betty Corning’. Nebraska Extension notes ‘Jackmanii’ is the most common clematis in Midwestern gardens.

In the South, Clemson recommends large-flowered types such as ‘Nelly Moser’ and ‘Henryi’ for South Carolina, with afternoon shade. It warns against sweet autumn clematis, Clematis terniflora, which is invasive in the Southeast, and suggests native virgin’s bower, C. virginiana, instead.

In California, UC Master Gardeners stress steady moisture during hot seasons. The evergreen C. armandii is sensitive to salty soil and water, which burns its leaf edges.