Clematis are of the Ranunculaceae botanical family. The majority of clematis are climbers. There are several hundred species of clematis, with the majority of these very hardy.
Clematis enable the gardener to have masses of bloom from early spring to late fall. To accomplish this, varieties with different bloom times can be grown together or planted in complimentary areas of the garden. Clematis can be chosen to enrich any garden, no matter how large or small. Some of species, if left to wander will easily grow 30' while others mature at 6-8'.
The hybrids are more compact with the majority maturing at the 8-12' range.
Most clematis varieties produce single flowers. These range in size from as small as 1" to 10". Some varieties produce double flowers, others produce both single and double flowers. Most double flowering varieties will bloom double on the previous season's growth, early in spring. They will then bloom single on the current season's growth in late summer or early fall. If pruned improperly, these varieties will produce single blooms only.
The blooms of the clematis often change color, some very markedly through the life of each flower, particularly when grown in the full sun. The pastel colors will hold their color best if grown in some shade. After the flowers are finished, the very attractive seed heads stay on the plant and make a welcome addition to flower arrangements. If left on the plant they sometimes remain well into winter.
How to Grow a Healthy Clematis
Article obtained from Ohio State Extension
Clematis have a reputation for being difficult to grow, however, like any other plant, if their needs can be met by the site and proper care, they will thrive. Clematis require full sun to grow best (6+ hours direct sun per day) though some dappled shade during the heat of the day is beneficial. Flowers of some red and blue large-flowered hybrids and the bicolors fade badly if they get too much sun and these should be planted in eastern exposures or partial shade. The site should be open enough to allow for air movement around the plants. Soil should be rich and well-draining with a pH close to neutral (7.0). Though the plant's stems and foliage should be in sun, the roots like a cool, moist environment. Clematis do not compete well with large tree roots. Most clematis will require staking so the twining leaf petioles can cling and climb upward, though some gardeners choose to let the plants sprawl over the ground, over woodpiles, other plants, etc.
Consider the ultimate size and vigor of the clematis being grown and match this to the support needed. Some support should be provided for vines unless they are left to scramble over walls, small trees or shrubs, or to sprawl over groundcover beds or grass. Supports must be thin and wire-like since this plant climbs by twining petioles that cannot grasp thick branches or heavy trellising. Arbors and pergolas are suitable for the larger, more vigorous types of clematis.
After amending the native soil for planting, dig a hole to accomodate the root system. Cut stems back to 12 inches in height. This will help the plant branch as it begins to grow and will reduce the chance of stem breakage during the planting process. Clematis are planted with the crown one to two inches below the soil surface (this enables the plant to recover should it be mowed off, damaged by animals or infected with clematis wilt). Once the plant is in the hole at the proper depth, fill in with the backfill soil, firm and water well to settle soil around the root system.
Because clematis prefer a cool root environment, plan to underplant with a groundcover or perennials that have shallow, non-invasive roots. Artemisia 'Silver Mound,' hardy geraniums, creeping phlox, coralbells, candytuft and most veronicas work well. A two-inch layer of mulch, low shrubs, or paving also provides a cooler root environment. Clematis may seem a bit slow to establish. In the first season, there may be little growth and few or no blooms. However, it is important to get the roots well established. Fertilize annually for rapid growth during establishment with a 3:1:2 or 4:1:2 ratio fertilizer. Fertilization may not be needed or desired once the plant is established and growing well. Plants will need about one inch of water per week during the growing season for good establishment.
Once the plant is well established, some basic care is needed on an annual basis. In dry seasons, watering deeply once a week is recommended. Renew mulch to a two-inch depth in late spring after the soil has warmed unless a groundcover or other method is used to cool the root environment.
Clematis can be transplanted in the fall, late winter or very early spring before growth begins. Dig as large a root ball as is possible (make sure soil is moist); the more roots preserved, the less the transplanting process will hinder the plant's growth. Make sure all the site requirements are met in the new location before moving any plant.
The main purpose in pruning is to help plants produce the maximum number of flowers. Annual pruning is recommended. Sometimes older, neglected plants can be cut back into older wood and new buds may break. Growth from old wood will likely be weak and slow, however. If no pruning were done at all, plants would still grow and flower profusely, though not where you may want them to. Some flowering would occur high in the plant and out of sight. Not all clematis can be pruned in the same way. There are three methods that can be applied to major groups depending on the time of year the plant flowers. No new growth must occur to enable the earliest flowering clematis to bloom, but the later flowering types must make new growth in order for flower buds to form. A few plants are not strictly bound to the following groups but may cross lines. Because vines will likely be entangled, make cuts carefully among the intertwining vines and spread and train them in various directions in order to cover the maximum possible area. This enables the plant to display its blooms rather than be bunched up.
Plants in this group bloom in early spring, generally in April and May, from buds produced the previous season. Prune these back as soon as possible after bloom but no later than the end of July. This allows time for new growth to produce flower buds for the next season. Remove shoots that have bloomed. You can prune out more vines to reduce the size or to form a good framework of branches. Do not cut into woody trunks. Plants in this group include: C. alpina, C. macropetala, C. armandii, C. montana and C. chrysocoma.
Large-flowered hybrids bloom in mid-June on short stems from the previous season's growth and often again in late summer on new growth (these blooms are smaller). Prune in February or March by removing dead and weak stems, then cut back remaining stems to the topmost pair of large, plump green buds. This cut could be a few inches to a foot or two from the stem tips. Plants in this group have the tendency to become bare at the base as they mature. Underplant to help conceal the stems. You may be able to force a flush of new growth from the base by cutting the vine back to 18 inches immediately after the flush of bloom in June. Plants in this group include: 'Nelly Moser,' 'Miss Bateman,' 'Lasurstern,' 'Duchess of Edinburgh,' 'Mrs. Cholmondeley' and others.
Plants in this group flower on the last two to three feet of the current season's growth. Some types begin blooming in mid-June and continue into the fall. This is the easiest group to prune since no old wood needs to be maintained. In February or March cut each stem to a height of about two to three feet. This will include removal of some good stems and buds. Eventually the length of the bare stem at the base will increase as the vine matures. Plants in this group include: C. viticella, C. flammula, C. tangutica, C. x jackmanii, C. maximowicziana, 'Perle d'Azur,' 'Royal Velours,' 'Duchess of Albany' and others.
The most devastating problem of clematis is a fungal stem rot and leaf spot caused by the fungus Ascochyta clematidina and commonly called "wilt." This is a disease on large-flowered hybrids. Small-flowered hybrids and the species and their cultivars are less susceptible to wilt. Symptoms include a sudden stem collapse typically as the flower buds are about to open, and within a few days, the stem and leaves turn black. Only one or perhaps several stems in a plant may wilt. The stem discolors and may exhibit lesions below the first pair of wilted leaves. Any part of the plant can be attacked down to and just below the soil level. The usual treatment is to remove the diseased stem below the wilted section, even below soil line. Plants usually recover from buds lower on the stem. Powdery mildew is another fungal disease that can occur on flowers and young stems, usually in July and August. It should be treated with a fungicide when first noticed as the fungus can disfigure leaves and flower buds, causing them not to open. Mildew often occurs on plants in poorly ventilated locations. If this is the case, consider moving the plant. Aphids may feed early in the season on new growth. Slugs may attack newly planted plants or even feed on bark of young stems. Earwigs may feed on blooms and foliage or bore into unopened flower buds. Rabbits and mice may feed on or girdle stems. Birds may feed on overwintering buds.