Rhododendrons and Azaleas for Home Gardens
The rhododendron is the most decorative of all evergreen flowering shrubs. The first to be grown in Great Britain, introduced over 300 years ago, was called Alpine Rose, a low-growing shrub with pinkwhich comes from the mountains of Switzerland. At the other extreme is a species called Rhododendron sinogrande, with leaves over 2 ft. long and 1 ft. wide, from the forests of north eastern Burma, south-eastern Tibet and Yunnan. Hundreds of other species in all shapes, sizes and colours have come from America, India, China, Japan, Russia; and one growing in Asia Minor, the Caucasus and Armentia — R. ponticum — has become naturalized in many parts of the British Isles.
R. ponticum is now used mainly for hedge-making and screening, and was one of the parents of the first hybrid ever to be raised, the work of a nurseryman in the Mile End Road, London, in 1820. Since that time so many hybrids have been bred that they now far outnumber the species.
From this vast range of different plants it is possible to select those that are suitable for all kinds of gardens and for any position. The more tender should be grown only where there is a heavy annual rainfall, but the tough little dwarfs grow out of character if they are treated too well; they are more suited to poor soils and the rock garden,
The tall, rambling growers are better in the woodland garden. Others grow in a neat, compact shape and may be planted in the mixed border, as specimens on lawns, or in pots or tubs. Some are more effective in a mass, others are better on their own, or against a background of different trees and shrubs.
Besides this variation in habit they have a great range of leaf patterns and colours. The young growth of some varieties is bright silver, on others it is red, and several have a thick brown felt on the underside of the leaves. This beauty in the evergreen foliage is almost more valuable than the flowers.
But the flowers are equally varied, and it is possible to have rhododendrons in flower outside from Christmas to August in all colours from pure white to a dark purple that is almost black. This wide range makes careful colour selection particularly important.
Technically, azaleas are rhododendrons. There is no botanical difference. But the plants that make up a large section of the great tribe of rhododendrons have been called azaleas.
They fall into two main groups: the deciduous varieties and the evergreens, often known as the Japanese azaleas.
Many of those that lose their leaves do so in a fine burst of autumn colour—an added attraction to the plants. The flowers range from white through yellow, pink and orange to red. Some varieties have a wonderful scent. They start flowering in May and continue until the middle of June.
The evergreens are neat bushes with a mass of small flowers from late April to June in colours from white to pink, salmon, orange and red. They are particularly useful for small gardens because they do not outgrow their positions.
Rhododendrons will grow only on an acid. If lime or chalk is present in any form there is little hope of success, except by making up banks of special soil or by growing them in pots or tubs. There are many ways in which to discover if soil is suitable for rhododendrons; the simplest of all is to observe the local vegetation — if gorse, heather, pine-trees and silver birch are growing in the district, then the soil is almost certain to be acid. Another method is to test with a cheap chemical soil-testing kit. It is possible that in the future rhododendrons may be grown in a soil containing some lime or chalk. The compound Sequestrene 138 Fe enables them to take up the iron in the soil which is normally “locked out” by the chalk.
Dig the ground well and work in some well-rotted cow manure or lime-free compost. This should be done a month before planting, which may be at any time in open weather from the end of September to the middle of April.
Rhododendrons are surface rooting and should not be planted deep; the same depth as before is a good guide, so look for the old planting-mark and plant so that it remains at soil level. Dig out a hole in the prepared ground, try it for depth by holding the plant in it with the roots just resting on the bottom. When the depth is right put peat or leaf mould round the roots (not underneath), fill in the hole and then tread firmly. Azaleas do not need peat as much as rhododendrons; they seem better able to root in ordinary soil. But firm treading is important for both—at the time of planting and about six weeks later. On heavy soil make only a shallow hole, put in the plant and finish off by covering the root ball with a mulch of peat or leaf mould.
Pick off the dead flowers as soon as they are over. This will allow the new growth to develop and form next year’s flower buds. In the spring give a mulch of peat or leaf mould, mixed with well-rotted cow manure, if available. Do this only when the ground is damp. Do not prune unless the plants grow so tall as to become unkempt. But if they do, cut them over in a regular pattern with secateurs. All the branches must be cut or the sap will rush to those that are left, giving a more unbalanced plant than before.
RECOMMENDED VARIETIES OF RHODODENDRONS:
The following hardyare all easy to grow and very decorative. The heights given are those to which the plants should grow from 15 to 18-in. plants in ten years under normal garden conditions.
Alice, 5 ft. Big pink flowers in mid-May.
Britannia, 3 to 4 ft. Compact growing. Gloxinia-shaped, scarlet flowers in late May.
Chionoides, 3 ft. Bushy variety with dark leaves. Creamy-white flowers in early June.
Christmas Cheer, 3 to 4 ft. Neat grower. Pink flowers in March and April.
Cynthia, 5 ft. Very reliable. Crimson flowers in May.
Earl of Donoughmore, 4 to 5 ft. New. Brilliant red flowers in late May.
Goldsworth Orange, 3 to 4 ft. A compact bush. Light orange flowers in late June.
Goldsworth Yellow, 4 ft. Pink buds which open to yellow in mid-May.
Jacksonii, 3 ft. Bushy. Pink flowers with deeper markings in March and April.
Jean Mary Montague, 4 ft. Bright scarlet flowers in early May.
Kluis Sensation, 4 to 5 ft. Compact. Intense scarlet flowers in June. Needs a little shade.
Kluis Triumph, 5 ft. Dark red flowers of good texture in May.
Moser’s Maroon, 5 to 6 ft. Deep red flowers in June. Leaves are red when young.
Mother of Pearl, 4 to 5 ft. Blush-pink flowers turning white in May.
Mrs. R. S. Holford, 4 to 5 ft. Salmon flowers in June. Opens slowly and lasts well.
Mrs. Wm. Agnew, 5 ft. Pink flowers with yellow eye in June.
Nobleanum, 4 ft. Compact. Flowers in various shades of crimson in January to March. One of the first to bloom.
Pink Pearl, 4 to 5 ft. Light pink dowers and deeper buds in May.
Princess Elizabeth, 5 to 6 ft. Red flowers with lighter centres in late May to June.
Professor Hugo de Vries, 5 ft. Dark pink flowers and deeper buds in May.
Purple Splendour, 4 to 5 ft. Dark purple flowers with almost black centres in May.
Scandinavia, 4 to 5 ft. Bushy. Deep red flowers in late May. Good foliage.
Souvenir of Anthony Waterer, 4 to 5 ft. Salmon-pink flowers with yellow centres in late May.
Starfish, 4 to 5 ft. Bright pink, star-shaped flowers and red buds in May.
Sweet Simplicity, 4 to 5 ft. Pale pink flowers with deep edges in late May. Makes a fine bush.
In the following list of deciduous azaleas the popular names are given first as these plants will be found in catalogues under “Azaleas” rather than “Rhododendrons” The correct botanical name is added in brackets. Unless otherwise stated they will all reach a height of about 4 ft. in ten years from a 1-1/2 to 2-ft. plant.
Azalea Ghent hybrids. Flowers late May, very hardy, and generally reach from 6 to 8 ft.
Altaclarense Sunbeam. Rich yellow, orange flare.
Coccinea speciosa. Brilliant orange-red.
Daviesii. Cream, well scented.
Raphael de Smet. Pink, double.
Azalea Knap Hill and Exbury Strain. These may be obtained as mixed seedlings or selected to colour. They have large flowers in large trusses in May and June, good colour and scent, and an autumn leaf display. There are many named sorts, a selection from which is:
Cecile. Salmon pink.
Golden Oriole. Yellow.
Silver Slipper. White, flushed pink.
Azalea mollis seedlings, 4 to 8 ft. A race of hybrids flowering in early May that may be obtained either as mixed seedlings, in which the predominant colour is the typical flame shade, or as seedlings selected to colours of pink, orange, red or yellow. These are less expensive than the named varieties of which the following are a selection:
Alice de Steurs. Apricot with deep shading in the centre.
Dr. M. Oosthoek. Orange-red. Golden Sunlight. Warm yellow.
Azalea politico (), 6 to 12 ft. Golden-yellow flowers in May. Wonderfully scented.
Azalea vaseyi () (Pink Shell Azalea), 8 to 10 ft. Pale pink flowers in early May.
Azalea viscosa (Rhododendron viscosum), 6 to 8 ft. White flowers in June. Very sweetly scented.
The following dwarf evergreen azaleas will not exceed 3 ft. in height in ten years under normal open-garden conditions.
Azalea amoemun (Rhododendron obtusion amoenum). Shades of pink, deepening to magenta.
Flinodegiri. Bright red.