Clematis enable the gardener to have masses of bloom from late winter to late fall. To accomplish this, varieties with different bloom times can be grown together or planted in complimentary areas of the garden.
The hybrids are on the whole more compact with the majority maturing at the 6-12' (2-3m) range.
Most clematis varieties produce single flowers. These range in size from as small as 1" (2.5cm) to as large as 10" (25cm). 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 than 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 can make a welcome addition to most flower arrangements. If left on the plant they sometimes remain well into winter.
Many of the clematis species are scented. Even though the scent is not powerful, the mass of blooms produced can fill the air with fragrance. The most highly scented is the tender species C. armandii. Of the large flowering hybrids, Clematis Vancouver Fragrant Star and Fair Rosamund are two large flowering varieties with a noticeable scent. Under the variety descriptions that follow, those with fragrance have been noted.
Clematis have some specific climate related requirements. Clematis grow and bloom much better if they have a dormant period of approximately six weeks. Night temperatures of about 45F (7.5C) or colder for a week or more seems to put them into dormancy. Gardeners should be aware that many of the excellent books on clematis originate in England. Their climatic conditions are quite different from those in most of North America. For this reason some of the notes in this publication will differ from the English recommendations. The notes that follow provide a North American perspective to gardening with clematis.