Soil preparation, proper planting depth and site selection are the most important factors in success with clematis. Clematis are long-lived perennials, and getting them off to a good start will pay long term dividends in plant health and vigor.
Clematis prefers a neutral to slightly acidic soil with a pH of 6.5 to 7.0. Do not add lime to the soil because this increases alkalinity.
Dig a hole 12 to 18 inches deep. Mix the soil you remove with 50 percent well-composted cow manure to provide natural nutrients and give the soil lighter texture. Refill the hole with the mixture you have made so that the roots of the plant are about 5 inches below the surface of the ground. This gives the plant extra protection from the cold and increases the chances of re-growth should the stems be broken off or the clematis wilt.
Clematis, like most vines, are heavy feeders. Never let them dry out, but keep them uniformly moist, particularly during a hot, dry summer. An early spring and fall mulching with well-composted cow manure feeds slowly without burning, helps protect roots, and keeps them cooler. Keep mulch about 4 inches from the stems.
The best planting time for clematis is in early spring or fall, during cool weather.
Clematis Site Selection and Support
The ideal location for clematis is in bright shade or filtered sunlight. The "full sun" suggested in many British publications, is far different than mid-American full sun. The root systems prefer the coolness of shade provided by mulch and by ground cover plants such as Vinca minor. Seek a location protected from strong winds, to avoid damage to the vines.
Young plants, and the new growth of mature plants, should be supported to provide directional training and avoid breaking the sometimes-brittle stems.
Fence, trellis, posts and arbors are good supports. Tie the stems carefully to the support. Most potted clematis come with a bamboo stake in the pot. Remove the plant carefully, keeping the stake in place. Incline the stake and the attached plant toward the support on which you want the plant to grow.
Clematis is especially effective when grown into shrubs, small trees, roses and other vines. The host plant adds protection, natural support and color and texture contrasts. Large trees are also a possibility. You may need to attach black nylon netting to the trunk so the clematis will have something to which it may cling. Select larger, more vigorous growing clematis like terniflora (Sweet Autumn), Comtesse de Bouchaud, or one of the hardier montanas, when growing them on larger trees.