Growing clematis: how to plant it, which varieties to choose, and how to prune.
Widely grown for their colorful flowers, clematis are among the most popular of vines. Perhaps most familiar are the modern hybrids with their large, showy flowers and restrained growth habit -- many will only attain heights of six to twelve feet, making them ideal for growing over shrubs and in other situations where a more rampant grower would smother its neighbors. Their blossoms encompass nearly the entire color spectrum and blooming times range from early spring to fall, depending on the variety.
In addition to the named hybrids, however, are the species clematis, which are sadly neglected. Among the most charming of these are varieties of Clematis alpina, which produce abundant nodding, bell-shaped flowers, quite different from the open saucer-shaped blooms of the hybrids. Clematis alpina is usually among the earliest clematis to bloom in the spring. Another species, Clematis tangutica, also produces bell-shaped blooms, of a bright golden yellow, but blooms in the fall. It is the only yellow clematis.
One of the greatest differences between hybrid and species clematis is the abundance of bloom. While the hybrids produce a handful of large, showy flowers, species such as the spring blooming Clematis montana are literally smothered with blossoms, although they may be only an inch across. Another difference is plant vigor -- Clematis montana, sweet autumn clematis and the evergreen Clematis armandii all are capable of reaching to twenty or thirty feet. Choose a site for these carefully.
When planting, provide all clematis with a cool root run. This can be done by mulching the root area or overplanting it with a groundcover that will provide some shade. A flat rock can also be placed over the crown of the plant. In addition to keeping the soil cool, this gives the base of the plant a bit of protection.
Because there are so many different types of clematis, there is often confusion over when and how to prune. For pruning purposes, clematis fall into three main groups. Group one blooms in the spring on the previous year’s growth. It does fine without pruning, but when shaping is desired, it should be cut back immediately after it finishes blooming. Group two blooms in early summer, with flowers forming on short stems that grow from the previous season’s leaf axil buds. In early spring it should be cut back to a pair of strong buds on all stems. Group Three blooms in the late summer or fall on the current season’s growth. Because it produces flowers on new wood, it will bloom most profusely if cut back each year in early spring to between 12 and 18 inches from the ground.