The commonest clematis colors of flowers are dark blues, purples and mauves, but this range is now being extended. We now have the clear white of, for instance, 'Marie Boisselot'; the beautiful yellow of C. orientalis 'Bill MacKenzie'; or the pink of 'Comtesse de Bouchaud'; the red of 'Ernest Markham' and 'Niobe'; the clear blue of 'Perle d' Azur'; the darker blue of 'Lasurstern'. The stronger the light in which the clematis is grown, the more intense the color. If there is little light, especially early in the season, the paler clematis may show a green tinge. Too strong light, on the other hand, can lead to fading. The stamens of many clematis are very conspicuous, often colored, and dramatically improve the impact of the flower. Most clematis flowers are single but a number of the cultivars are double, and a few almost take on the character of a paeony. While most clematis tend to open to a flat shape, there are many variations on this. There is the tiny star of blue-white C. flammula, the single bell of C. alpina, the double bell of C. macropetala, the tubular bloom of C. rehderiana, the tulip shape of C. texensis and the lanterns of C. tangutica and C. orientalis. In the species the blooms tend to be tiny but the plants make up for it by producing blooms in large numbers. The hybrids, on the other hand, can produce flowers that may be up to 25 cm (10 in) across. A well grown clematis can be very productive of flowers. There may be as many as 500 flowers on a well established plant and in the Jackmanii group this can rise to 1500. The Japanese, who specialize in growing clematis in pots, expect to get up to 200 flowers in a pot plant. Amongst the species, of course, the flowers are smaller but make up for this with a cascade of blooms. Some of the blooming can be almost continuous through the summer months.
Clematis vary greatly in height from the 8 cm (3 in) of C. marmoraria, the delightful alpine New Zealand clematis, to C. montana varieties which can soar 12m (40ft) up a tree. Tall, early species include C. armandii, C. montana, C. chrysocoma, C. spooneri. Later, in the summer, comes C. campaniflora and later still, in the autumn, C. viticella varieties, C. flammula and C. rehderiana. The tall growing species are particularly valuable for covering an unsightly feature in the garden or climbing a tree. The tall-growing large bloomers are good for peeping in at a first floor window, or for reaching round a corner, or for stretching over a wall. The short-growing cultivars can be equally useful. They can be grown with the tall-growing varieties and hide the bare lower stems of the latter. They are useful too in small patio areas or for growing over low walls or low shrubs.
A great joy is that so many clematis are perfumed, and some very strongly so. Sadly, this is not true of the large-bloomed clematis: amongst these only 'Fair Rosamond' can claim any strong scent, and 'Barbara Jackman', 'Duchess of Edinburgh' and 'Sylvia Denny' are faintly perfumed. The picture among the species, however, is very different: starting from C. armandii in the early spring, to C. rehderiana in the late autumn, there is a procession of sweetly scented clematis.
Some clematis are grown for their eye-catching seed heads. These are bordering on the spectacular in many of the wild species. Particularly striking is C. vitalba in the UK. The alpina and macropetala species are the first to display their seed heads in the summer and are followed in late summer by the silky seed heads of C. tangutica and C. orientalis, to be followed still later by the silver grey of C.flammula.
Some 'clematarians' have to contend with extremely low, unfavorable, temperatures. In these conditions, there are ways to success. For instance, the local native species, which are likely to be hardy, can be grown. Again, the species alpina and macropetala are hardy to very low temperatures; C. fargesii and C. recta can do well. Furthermore, the late-flowering species such as C. viticella, c. x jouiniana, C. orientalis and C. tangutica can be grown, but cut down to the ground in late autumn; if the roots are well protected they will survive the winter. The same treatment can be given to some of the late-flowering cultivars. Some of the cultivars have a good reputation in cold climates and these include 'Victoria', 'Hagley Hybrid', 'Jackmanii', 'Perle d' Azur', 'Niobe', 'Gipsy Queen', 'Comtesse de Bouchaud', and 'Ville de Lyon'. As a last resort, in extreme conditions, the clematis can even be grown in containers and brought indoors in the winter.
What are the faults of clematis? Some would complain that in winter many clematis look black and unsightly without leaves. In most cases, however, this problem can be easily overcome by pruning late-flowering species and cultivars in the autumn -a partial pruning -to be followed by a hard pruning in the spring. In those varieties requiring light pruning, the bare stalks can be hidden by planting shrubs in front of them. Some clematis are said to have bare bottoms even in the flowering period. This can be dealt with by planting a short-stemmed clematis alongside the long-stemmed clematis. Or again, it is possible to bring down some of the high flowering trusses nearer the ground. The very vigorous montanas seem to be the most notable sufferers of bare stems in winter. Thus, these should be planted where they are not seen from the house during this period. Then, in the late spring, one can walk to a vantage point to enjoy their spectacular flowering. Another complaint is the tendency of some of the more vigorous clematis to tangle with one another, thus making a thick wad of bloom. This is really the result of defective pruning which, if correctly done and with proper training, will spread the clematis plant out so that the flowers can be seen to advantage.