The genus Clematis contains a wide array of garden plants that vary in their bloom season from early spring until late summer. Bloom sizes also vary, ranging from 1/2 inch to 8 inches in diameter. Vining clematis is more familiar to most gardeners, but there are also short, bushy varieties that need no support. One thing that all clematis have in common is their fluffy, plume-like seed heads that extend the plant’s season of interest. The showy flowers and seedheads are both well-suited to flower arrangements.
Clematis needs full sun or partial shade and a moist but well-drained, humus-rich soil with a pH of 6.5 or higher. The plants prefer a cool, shaded soil, so provide thick mulch, particularly during warm, summer months. The east side of a building is ideal, providing afternoon shade to keep roots cool during the hottest part of the day. Hardiness varies according to the species, but most are hardy in U.S. Department of Agriculture hardiness zones 4 through 8.
Clematis likes a weed-free soil, but you can easily damage the shallow roots when working the soil around them with a hoe. Mulch helps discourage weeds, making it easier to remove those that sprout by hand-pulling. If your soil is acid, apply lime to adjust the pH. Water to keep the soil evenly moist but not soggy, and fertilize annually in spring with a slow-release fertilizer. Cut the perennial vines back to 6 inches from the ground in late fall or early spring. Early flowering vines are an exception. They produce flowers on new growth, so prune them immediately after they flower, cutting the vines back just enough to control the size.
Clematis vines climb by twining their leaf petioles around a supporting structure. The structure must be thin for the vine to attach itself. When planted against a wall or other solid structure, string galvanized or plastic coated wire against the structure for support. Allow 3 to 4 inches between the supporting structure and the wall for ventilation. Clematis climbs lattices and trellises readily without tying.
Clematis is susceptible to damage from caterpillars, mites and nematodes. Caterpillars feed on the leaves and can do serious damage if left unchecked. At the first sign of caterpillars, treat the vine with Bacillus thuringiensis (Bt). This low-risk insecticide is fatal to caterpillars but doesn’t harm humans, pets or other wildlife. Not true insects, spider mites are closely related to spiders. They suck sap from foliage, causing spotted leaves and may prevent flower buds from opening. Treat them with insecticides containing insecticidal soap, neem or pyrethrin. Nematodes live in the soil and feed on roots. The only way to get rid of them is to sterilize the soil. Otherwise, you can plant clematis elsewhere and use the nematode-infested soil for plants that aren’t susceptible to the pest.