Culture Notes
These vines prefer cool, rich, moist, relatively acidic, well-drained soils, and one should never allow these plants to become too dry. Many need to be placed in an area of the landscape that receives full sun but allows the roots to remain cool. There are some, such as C. alpina, C. macropetala, and C. chrysocoma, that are adapted to partial shade. Some, such as C. texensis, are adapted to hot weather. To keep the roots cool, spread several inches of an organic mulch for several feet around the main stem. Prune these vines after flowering, if desired, to maintain the plants general shape.
Flowers come in every color except green and black. Some are very fragrant. There are more than 250 species of Clematis and about 5,000 cultivars to choose from. They can be planted at the base of any support. The best time to plant in the north is spring. Cutting back young plants about one-half will encourage branching and lead to larger flowers. Prune spring flowering plants (those that bloom on previous season's growth) only to remove dead branches and to control the plants size, if you wish. Plants that flower on new and old wood (those that flower a little latter) should have weak shoots pruned back to a strong bud or to an aggressive lateral branch and dead branches should be removed. Fall bloomers flower on new wood, so they are best pruned in the spring as new growth emerges.
Pests, Diseases and Damaging Agents
The hybrids of Clematis are bothered by stem rot and leaf spot. Leaf spot will first appear as a small water-soaked area which becomes tan with a red margin.