Notes on Alpine Rhododendrons
D. W. James
Many of the Rhododendrons sent home by explorers in recent years have been of the dwarf varieties growing among the rocks in Central Asia, and as they are being grown to flowering size, the finer forms are becoming popular, both for their own beauty and adaptability and for their value in hybridizing. For growers with limited gardening space, and also for landscaping with modern low buildings, they are particularly valuable.
Prominent among the plants which fit into this category are many of the alpine species and their hybrids, which are only recently becoming known to United States enthusiasts. Since rhododendrons of the alpine types vary considerable when grown from seed, it is important that careful selection should be made from seedlings, and only the choicest forms kept. The plants grow in small compact bushes, with twiggy branchlets, ranging in height from only a few inches to a few feet, the leaves are usually small, more or less scaly often changing color in the Fall of the year to red and russet, and are often very aromatic. The colors range from whites through pink, yellow, mauve, lavender and blue to purple and red. Flowers vary in size from small blossoms in tiny trusses to single flowers of much larger size, either of which will cover a plant completely, making a mass of color.
In the Northwest, one of the best known of the creeping alpines is R. radicans, although it is considered quite rare in England. It is a member of the R. saluenense series and is quite typical of the series, being low, prostrate and 1-3 flowered.
A very large group of the alpine type rhododendron, are those of the R. lapponicum series, found mainly at high altitudes of Yunnan and Szechuan, a large natural group of low growing shrublets often forming extensive carpets over the landscape of Western China. They are found in a wide range of colors, some a bright magenta, and others in mauve and blue, and a few in yellow. They bloom early from seed.
An outstanding member of this group is R. cantabile , meaning "worthy of song," which is certainly self descriptive, for it is an impressive sight when covered with its multitude of dark violet colored flowers.
Another fine example of this group is R. yungningense, which we have grown from seed received from England. It is a beautiful shade of blue with quite large flowers for the type. R. telmateium is not so well known, but is a striking plant when covered with its deep rosy-purple flowers, with white corolla throat.
A group which should not be overlooked, is the R. glaucum series, members of which are taller growing, ranging from two to five feet, or in the case of R. genestierianum, up to twelve feet. Probably the best known of this species is R. glaucum itself, which is pink with bell shaped flowers forming a loose truss of five to six flowers. A good form of R. pruniflorum with flatter flowers of plum-purple or nearly crimson or violet is a must in this series, as is R. pemakoense which covers itself with pale purple flowers early in the season.
Closely allied to the glaucum group is the boothii series, which are small shrubs up to four feet high, rarely epiphytic. Flowers are few in a terminal cluster, or rarely solitary, bright yellow, or very rarely magenta-rose with a purplish tube as in R. tephropeplum, or pure white as in the case of the lovely R. leucaspis. See Fig. 12.
Whether or not it could be considered a true alpine, R. yakushimanum should not be left off the list of desirable dwarf growing plants. It was discovered on Yaku Island and named by the Japanese botanist Nakai. While information on it is rather scanty, a fine specimen two feet six inches high and nearly four feet through, covered with hundreds of flowers, was given an F. C. C. by the Royal Horticultural Society in 1947.
In the opinion of this grower, the queen of all the alpine species is R. moupinense, which in its more select forms is an outstanding plant against any competition. The foliage is round, dark green; the buds are a bright pink, fading to a pure white as the blossom opens, with maroon colored spots on the upper petals and maroon stamens. The fully opened flowers measure three to four inches across and are borne two to four in a truss. The plant grown here is about two feet high and covers itself with buds each year. Its only fault is that it usually comes into bloom in February and unless it is protected the flowers are sometimes spoiled by frost.
Since the various alpine species cover a great number of varieties, it would be impractical to try to cover all of them, but their importance in the field of horticulture is unlimited. Selected forms are ideal for use as border or edging plants, taking care to choose those which grow as well knit shrublets, covering themselves with bloom. R. sphaeranthum and R. racemosum adapt themselves well to such use. Others are equally useful for rock garden planting or to be inter-planted with perennials or bulbs.
Some hybridizing has been done with members of the alpine groups with quite remarkable success. Such well known hybrids as R. 'Blue Tit', R. 'Blue Diamond', R. 'Impeanum' and R. 'Sapphire' are worthy of attention in anybody's garden. Others coming into prominence may not be strictly alpine but should fit well into similar usage. These are the fine new dwarf hybrids such as R. 'Elizabeth' and R. 'Arthur Osborne' in red, and R. williamsianum with its hybrids for large flowered pink shades.
The culture of alpine rhododendrons should not be difficult when it is remembered that they are found usually at high altitudes, clinging to rocky banks or screeds, where there is considerable moisture in the air, but drainage is perfect. They like sunshine but need plenty of water. In their natural habitat they are covered with snow for many months of the year, and the slowly melting snow keeps them happy even though the soil they grow in is scanty.
F. Kingdon Ward in his latest book "Rhododendrons" says, "There should be no difficulty in finding plants to suit all fancies, since there are nearly a hundred dwarf species of rhododendron known, more than fifty being in cultivation today. Not all of them are on the open market, perhaps, but the majority are. They may cost quite a lot, but that is really an advantage, not only for the plant, but for you too. If you pay ten shillings for a small plant which will not flower for a year or two, you are more likely to spend some time studying its whims and needs than - if you had paid only sixpence for it. You want it to stay alive at least until it flowers, and to ensure that, you are prepared to take a little trouble over it."