Some Observations of Rhododendron Foliage
By Mary Greig, Royston, B. C.
No one, now-a-days, would deny that rhododendrons are one of the most popular of all flowering shrubs for temperate and mild gardens-beautiful in flower either as single specimens, in groups or massed. What is rarely noted is that, aside from their flowering, they offer for interest and beauty a variety of foliage and habit far beyond any other genus. In this field the species decidedly outdo their better known hybrid progeny.
The most usual virtue of a plant when foliage is the chief reason for inclusion in the garden is fine Fall coloring, or alternatively, as when conifers, junipers and yews are used, it is for their continuing green, grey blue or golden mass, which varies hardly at all during the year. I am not attempting to argue that none of the latter should appear in our gardens-where grounds are big enough to allow them to mature, the symmetry and grace of many of them is unsurpassed by any other evergreen tree and the true dwarfs too are indispensable. What I am trying to say is that both for Fall colour among the deciduous azaleas, and for the varying greens, blue-greys and greens with a coppery sheen, the evergreen rhododendrons give us a year-round joy sufficient to warrant a place in temperate gardens, even if they never flowered at all!
The "ordinary" rhododendron leaf expected by most people who have had little experience with the family is the clean, medium green oblong and rather pointed leaf of the older hybrids, which is, of course, also a fairly typical leaf for a large number of the species, and quite a fine leaf, too, making a solid and comely bush or small tree at all times, and a glory of pink, red, cream or white in blossom. We all know them, delight in them while they give their yearly display, and then, as far as the eye concerned, forget all about them.
Even in that medium sized and shaped leaf there is variety to he had, as for instance in the Taliense (from the Tali Range, Yunnan) series. In the subdivision adenogynum (meaning "with a glandular ovary") the leaves are backed with bright cinnamon, fawn or rusty red indumentum, or sometime; off-white-to the touch like a soft blanket. The habit of that particular group, of holding the new leaves up, shows the underside admirably, and when in new growth, stems, shoots, and the upper sides of leaves are coated, in some of the species, with temporary foxy-red plush. Some of this group have to rely on their beauty of habit and leaf as their only virtue for a good many years, one has to admit, for they can can be extraordinarily slow to flower.
Then there are the roundish waxen leaves of R. thomsonii, and others, having a bloom on them like a ripe greengage. The enormous leaves of the Falconeri and Grande series, some from 14 to 20 inches in length and 5 or 6 inches across are magnificent. These vary from light to deep green, having very deeply veined, rugged and leathery top surface, with white, fawn and brown thick felt on the undersides. They are almost all big shrubs or trees eventually, though some of them are slow-growing, and slow to flower.
Some of the loveliest leaves adorn the members of the Triflorum and Cinnabarinum series, two groups similar in habit, slender bushes of from 4 to 8 feet, or more, with leaves of from 2 to 33 or 4 inches long and an inch or so across-oval or pointed and very floriferous. R. oreotrephes (meaning "mountain-bred") is particularly fine with small oval leaves of misty grey, smooth and glossy, and stem and midrib of orchid pink, very noticeable in the new growths. It retains its delicate grey at all seasons. Another beautiful grey-leaved one, but slightly smaller in leaf, and considerably smaller in stature, is R. concatenans. It has small yellow bell-like flowers, white R. oreotrephes has flowers of almost the same orchid-pink as shown in stem and midrib. R. cinnabarinum also has an egg-shaped thick glossy grey-green leaf, very attractive with the cinnabar-red tubular flowers, and for long after the flowers are gone. Still among the greys, there is the Trichocladum ("with hairy twigs") rhododendron, lepidostylum. It too is yellow-flowered, and has small pale green leaves covered with grey hairs, the whole bush is low and spreading and always calls forth comment.
Rhododendrons lanatum ("wooly") and tsariense (from Tsari, S. E. Tibet) though very like each other, are quite unlike any other plant we know. They belong to the Campanulatum ("bell shaped") series. The leaves of one are a medium green, the other dark, but both wear a thick covering on their upper surfaces of white silky hair, which gradually disappears except towards the stem, where mature leaves still wear white whiskers. The underside. are coated with fawn or deep cinnamon wool.
Smallest of all the blue-greys are some forms of R. fastigiatum (erect) and impeditum (tangled), very attractive, compact shrublets no bigger than a heather. These last, along with most of their small brethren of the Lapponicum (from Lapland) series, usually flower twice too--in April and again in August or September.
Some of the Saluenense (from the Salween Valley) series, another dwarf group, also have grey young growth, becoming green later, and some have a lovely aromatic scent, when rubbed.
A number of the ordinary green Triflorums have vivid red new growths, so bright as to seem at a distance that the shrub is in flower, particularly R. lutescens ("becoming yellow") and the tall form of R. keiskei (named after Ito Keisuke, a Japanese botanist of the last century) both these have small bright yellow flowers. If they are grown in the shade the coloring is not so noticeable. Among the deciduous azaleas, R. schlippenbachii (named after Baron von Schlippenbach, and found in Korea, Manchuria and central Japan) and R. vaseyi (named for G. S. Vasey who discovered the species in North Carolina in 1878) both give superb Fall reds and yellows. They both flower in early spring before the new green leaves appear, and there are many others.
Among the more orthodox green leaved species, many have every conceivable tone of green - particularly in new growth-pale, deep, bright, soft and some so strong and arresting that the green might be called virulent. Every texture too is offered, thick, leathery, waxy, papery, bristly, silky and so on. Shapes and sizes show as much variation, from minute to enormous and from almost round to lanceolate and almost linear. All rhododendrons make their new growth after flowering, so their period of interest is prolonged thereby. It would seem, too that many of the very large-leaned one, become much smaller leaved when flower age is reached, which is a pity, but one can't have everything. Those of us who can grow some of this most delectable family should be duly thankful!