This section is from the book "Commercial Gardening Vol4", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
Although there are over forty species of Clematis known, all interesting, and many beautiful, they are of little value commercially in comparison with the garden hybrids that have appeared during the past sixty or seventy years. Hundreds of thousands are raised every year. The usual method of propagation is by grafting under glass from January to March. The principal stock used is that of C. Vitalba, the only British Clematis, popularly known as Traveller's Joy, Old Man's Beard, White Vine, etc. Stocks of C. flammula and C. Viticella, both natives of southern Europe, are also used, but perhaps chiefly on the Continent.
The process of grafting consists in splitting a shoot carefully through a joint with a sharp knife, so as to make two scions from the buds, which are opposite each other. This work is done in a warm greenhouse, and it is astonishing to see how quickly and deftly an experienced gardener can perform it. Side grafting is usually practised, the scions being attached to the top piece of the root fibres with a piece of raffia. The whole is then placed in a 2 1/2-in. pot in gritty soil, and placed in a close frame in a temperature of 70° to 75° F. Union soon takes place, and the young grafted plants are taken out at the end of a week or two to make room for succeeding batches. During the summer months, from June onwards, the plants are placed in the open air, having previously been shifted into 5-in. pots. They are plunged in beds of sifted ashes or tan, and each one is tied to a slender stake and labelled, for sale during the autumn, winter, and spring months. Another method of propagating Clematis adopted largely by some growers is to take cuttings of the ripened shoots about May or early June. Each cutting has two joints, and the leaves are retained to the upper one. About 100 such cuttings are inserted in a shallow wooden tray or cutting box, using a gritty soil. They are kept shaded and close under glass for a short time until "callused", but are placed in the open air about the end of July or August, fully exposed to the light and air, and are watered as required. They are shifted from the cutting boxes during the winter months, each one being placed in a 3-in. pot, and under the genial warmth of a greenhouse are started into growth. Clematis raised thus on their own roots are preferred to grafted plants by some. For early summer trade, established Clematises are brought into flower in April and May by placing the plants in heat in batches from January onwards. The stems are either twisted round stakes or tied out on wire trellises in the form of balloons, as shown in fig. 420, or some other design.
Fig. 420. - Pot-grown Clematis Princess of Wales, trained on Wire Trellis.
There are several groups of garden Clematis, the best known being:
The typical hybrid was raised and flowered in 1862 by Messrs. Jackman, of Woking, by crossing C. lanuginosa with a C. Hendersoni, the latter a hybrid raised from C. Viticella and probably C. integrifolia and distributed in 1835. It is still one of the most popular, and its intense violet-purple crosslike flowers are seen in almost every part of the kingdom from July to October. Other varieties of Jackmanni are superba alba, white faintly tinted; Snow White, pure white; Madame E. Andre, velvety red, fig. 421; Lady Northcliffe, deep lavender; Madame Baron Vieil-lard, lilac rose; Prince of Wales. deep purple; Star of India, reddish violet tinted with purple and barred with red; rubra, rich crimson purple; velutina purpurea, blackish mulberry.