Among flowering vines, few have flowers as spectacular as the clematis. It has been more than 150 years since this vine was first hybridized to improve flower size and color, and improvements continue to be made.
The large flowers are available in purple, blue, mauve, pink, red and white.
These hybrids do not become rampant vines, and may provide color from late spring to late summer. Some varieties have a fairly long flowering period, while others are shorter but may bloom again later in summer, although less intensely.
Although most of the popular varieties are hybrids, there are about 230 species of clematis native to temperate climates. Some species may be grown to provide flowers more unusual in form and color than the hybrids. The golden Chinese clematis, Clematis tangutica, produces bright yellow flowers. The well-known sweet autumn clematis, Clematis maximowicziana, are fall blooming. Some clematis species are not vines, but form small bushes, which may be cut back to the ground in fall. Clematis davidiana, which has blue flowers, is an example of this type.
Clematis plants grow best in well-drained soils with liberal amounts of organic matter. Clematis roots are best when cooler than the tops, so a heavy mulch on the soil around the base is beneficial. Do not pile mulch up over plant stems.
Clematis are somewhat sensitive to soil pH, although they can grow well in a pH between 6.0 and 7.0. Soils more acid or more alkaline often lead to iron chlorosis or other problems.
Clematis can be grown in sun, but have some shade tolerance. Flowering, however, is best when plants get some direct sunlight each day. Around the home, an east location is ideal, but west and south locations may also be used. Soil moisture stress can be damaging to clematis, so be prepared to water during drought periods, especially in the first several years after planting.
Clematis hybrids are normally grouped according to the species of the dominant parent in the hybrid. Therefore, you may find varieties belonging to the Jackman group, Languinosa group, Patens group, Viticella group and Florida group. The Jackman group, which is the oldest, flowers later than some, but once flowering starts, bloom often continues into the summer, but with less quantity.
Popular varieties include ‘Contesse de Bouchard,’ ‘Crimson Star’ and ‘Perle d’ Azur.’
The Languinosa group contains some of the most spectacular hybrids. A few of the many varieties are ‘Elsa Spath,’ ‘Henryi,’ ‘Nelly Moser,’ ‘Ramona’ and ‘W.E. Gladstone.’
As a group, these varieties flower slightly earlier than the Jackman varieties.
Plants may be cut back 2 to 4 feet from the base in spring to produce vigorous, free-flowering new growth.
The Patens group flowers primarily in late summer, and is the least popular of these five groups. Patens varieties flower on previous year’s wood, so severe pruning should not be done in spring. Pruning after flowering to stimulate good growth for next year’s flowers is the best approach for plants of this group. Examples of this type include; ‘Lincoln Star’ and ‘Miss Bateman.’
The Viticelli group may also be pruned back hard in the spring. If high vine growth is wanted, spring pruning should be minimal and the past season’s wood retained unless there was winter damage. This group is primarily summer flowering. A few popular varieties include ‘Ernest Markham’ and ‘Ville de Lyon.’
The Florida group is slightly less cold hardy than the others, but provides some of the most spectacular double flowers among the hybrid clematis. Previous year’s wood must be retained for flowering, so pruning should not be done until after flowering. Two outstanding varieties in this group are ‘Belle of Woking’ and ‘Dutchess of Edinburgh.’
Leaf spot and stem rot are two common disease problems of clematis, especially after wet weather or if planted in a location where excess moisture with poor air movement and high humidity are common.
Clark Beusse is the Dawson County extension agent.