RHODODENDRON

FLOWERING SHRUB. These well-known evergreen shrubs flower mostly in late spring and early summer, although some species and hybrids, notably the rosy-purple Rhododendron praecox and the scarlet-crimson R. nobleanum, bloom in winter. The blood-red Ascot Brilliant and Handsworth White also flower early — between February and April, depending on the weather. The colour range comprises pink, crimson, mauve, purple, yellow, apricot, white and intermediate shades. Note that rhododendrons sometimes have an ‘off’ year when no flowers are produced. This usually happens the year after a heavy crop of bloom. The do not bloom freely until well established. Azaleas, including the varieties of Azalea indica (Rhododendron Simsii) which are bought in flower from the florist to grow in a living room, are now included in the genus Rhododendron, although still often catalogued under azalea. They include both deciduous and evergreen forms and are discussed later.

Cultivation:

Rhododendrons demand an acid soil, I.e. no lime or chalk, and it is useless trying to grow them on limy soil, as they rarely make proper headway, no matter how much trouble is taken over soil preparation. Note that Rhododendron ferrugineum and R. hirsutum, both known as the Alpen or Alpine Rose, which grow to about 3 ft. with rose-coloured flowers in early summer, are exceptions. They are quite happy on lime (R. hirsutum is always found on limestone formations). There are white forms of these species. Light, medium and heavy soils are all suitable, provided they are acid (a BDH Soil Indicator -will soon tell you if your soil is acid or alkaline). Good results are often obtained on neutral soils. Dig two spits deep and work in plenty of leaf mould, and peat, plus sharp sand on heavy land. Rhododendrons are not deep-rooting and it is best to place the leaf mould etc. no deeper than say 15 in. The peat should be mixed freely with the soil round the roots. Well-rotted cow manure is also beneficial but must be kept away from the roots. Slight shade is usually advisable, especially for azaleas. Do not plant alongside big trees or on a hot dry bank as rhododendrons prefer soil which is reasonably retentive of moisture. They are relatively slow-growing. Plant from October to April and allow ample space as rhododendrons grow outwards as well as upwards. A minimum spacing of 8 ft. is usually advisable if each specimen is to show to maximum advantage. Some of the shorter-growing kinds can be planted closer — see Choice of Varieties:. An annual mulch of damp peat, leaf mould, lawn mowings or cow manure applied in April will help to keep the roots cool. Water, if necessary, during the first summer after planting. If growth is backward, give a top dressing of sulphate of ammonia in March. Always remove dead flowers as their retention tends to weaken the plant. Any suckers (growths from the stock on which the plant has been grafted, e.g. Rhododendron ponticum) must be removed directly they are noticed. Chop them off with a spade.

Choice of Varieties: There are innumerable species, hybrids and varieties and the following represents a limited selection, though in a good colour range. As previously stated, spacing of individual bushes should usually be not less than 8 ft. but the shorter kinds, e.g. those growing to about 4 to 5 ft. tall, can be planted rather closer. The same applies to the dwarf rhododendrons like the purple-blue R. impeditum which only reaches 1 ft., or the shell-pink R. Williamsianum which grows to about 2 ft. and as much through.

Ascot Brilliant: Blood-red. Grows to about 5 ft.

R. auriculatum: the latest of all rhododendrons, of tree-like growth, up to 30 ft. Large, fragrant white flowers in July and August.

Blue Diamond: rich bluish-mauve. Compact grower to about 3 ft.

Britannia: vivid crimson-scarlet, gloxinia-shaped flowers. Height about 5 ½ ft.

R. caucasico-pictum: light pink with a red blotch. Height about 7 ft.

Cornish Cross: rich rose-pink. Height about 10 ft.

Elizabeth: trumpet-shaped, dark red flowers, 3 in. across. Low spreading growth to about 3 ft. Prefers a cool position.

Gladys: creamy-yellow buds open to cream and purple flowers. Height about 7 ft.

Goldsworth Orange: pale orange. Height about 3 ½ ft.

Goldsworth Yellow: primrose-yellow. Rather taller than Goldsworth Orange.

Gomer Waterer: blush-white. Height about 5 ft.

Handsworth White: name describes the colour. Height about 31/2 ft.

John Walter: rosy-crimson. Height about 10 ft.

R. Loderi: grows up to 20 ft. with large, oblong leaves, 6 — 10 in. long.

Huge fragrant flowers as much as 6 in. across. There are several rather similar varieties of this species, e.g. King George, Pink Diamond and Titan, all light pink or white.

Lodefs White: pale pink buds opening to pure white flowers. Height about 15 ft.

Moonstone: creamy-pink. Makes a rounded bush to about 31/2 ft.

Moser’s Maroon: name describes the colour. Height about 7 ft.

R. nobleanum: rosy-scarlet. Blooms in late winter and early spring. White and pink forms are available. Height about 15 ft.

R. obtusum amoenum: vivid magenta flowers, often semi-double, on a 2 ½ ft plant.

R. odoratum (fragrans): white tinted lilac. Very fragrant. Compact grower to about 5 ½ ft.

Pink Pearl: probably the best known of all rhododendrons. Rose-pink passing to blush-pink. Height about 5 ft. Purple Splendour: dark purple. Height about 5 ft.

R. ponticum: the least expensive rhododendron and the most widely planted. Does well in full sunlight. Used as a stock for grafting and is naturalised in some places. The mauve-pink flowers are borne on a plant which reaches 15 ft. or more with an even bigger spread — 20 ft. on favourable soils. Makes an excellent hedge.

R. praecox: often blooms at the end of January. Rosy-purple flowers on a spreading 31/2 ft. plant. Sometimes tolerates a little lime in the soil. R. radicans: has a prostrate habit, only reaching 3 in. with correspondingly small bright green leaves. Colour deep purple. Ideal for rock gardens. R. williamsianum: another attractive rockery species making a low, spreading bush, about 2 ft. high and 3 ft. through. Foliage bronze in the early stages, passing to bright green. Shell-pink, bell-shaped flowers.

Propagation. Commercial growers graft the particular species or variety on to seedlings of Rhododendron ponticum but this method is really beyond the scope of the beginner as it is necessary to grow on the seedlings for several years and then graft in winter in a warm greenhouse. Layering is more practicable but can only be undertaken with well-established bushes with sufficiently long branches near soil level. These are pegged in the ground to a depth of 3 in. Unless the branch is too hard make a slit in the portion to be buried, as this stimulates quicker rooting. Note that most rhododendrons may not take root for at least a year.

Insect Pests and Fungus Diseases:

Both the pests described below are usually more troublesome in the south of England. Rhododendron Bug or Fly. This sucks the sap from the foliage causing numerous small yellow or chocolate spots, especially on the undersides. Infested leaves have a ‘rusty’ appearance. Hand picking and burning the leaves usually suffice for minor attacks, but if severe spray with insecticide in May, taking care to drench the undersides of the foliage where the eggs are laid an the young bugs ‘operate’.

Rhododendron White Fly. This pest causes rather similar damage to the rhododendron bug. The adults are found on the undersides of the topmost leaves of the shoots from mid-June to mid-July. The nymphs excrete a sticky substance known as ‘honeydew’ which furnishes nourishment for the growth known as sooty mould (a disorder also affecting rose trees; see ROSE — Fungus Diseases). The larvae feed on the undersides of the foliage from late summer to early spring. Spraying with insecticide in late Jnue is recommended.

Bud Blast. A comparatively new fungus disease in this country. Infected buds turn brown in late summer or early autumn, and later the entire bud becomes black. So far no effective control has been found, but research continues. Meanwhile, it is best to burn diseased buds and cut back the infected shoots by about 3 in.

AZALEAS:

All azaleas are technically rhododendrons. Nevertheless, catalogues often still treat azaleas as a separate genus; accordingly they have been separated here. They require the same soil and cultural attention as the rhododendrons proper, I.e. no lime, peat and leaf-mould when planting, slight shade and prompt removal of all dead flowers. The dwarf kinds can be increased by cuttings of half-ripe wood in July, rooted under cloches.

Azalea pontica (Rhododendron luteum) is the common yellow azalea, a plant for every garden where the soil is acid or neutral. It can be naturalised in woodland or massed where space permits. The very fragrant honeysuckle-shaped yellow flowers appear in May, the foliage turning red, purple and orange in autumn. Used as a stock for grafting. Height about 10 ft.

Deciduous Azaleas. There are several groups of deciduous azaleas.

The Mollis group is extra hardy, the flowers appearing in early May before the leaves. They grow to about 4 ft. There is very little fragrance.

Unnamed seedlings will provide a pleasant range of colours and work out cheaper than named varieties. Nevertheless, the following can be strongly recommended, with the proviso that late spring frosts may injure the flowers.

Babeujf: salmon-orange.

Comte de Gomer (Consol Ceresole): clear pink.

Dr M. Oosthoek: orange red.

Hollandia: orange-yellow.

Hugo Hardyzer: deep scarlet.

Jcoster’s Brilliant Red. another brilliant orange-red.

Mrs A. E. Endtz: rich yellow.

The Ghent azaleas are a little taller, reaching about 5 ft., and mostly very fragrant. They bloom at the end of May or early June, accordingly usually escaping late spring frosts. The honeysuckle-like flowers are more tubular in shape and rather smaller than those in the Mollis group.

The foliage often colours well in autumn.

Altaclarense Sunbeam: yellow with orange blotch.

Bouquet de Flore: bright pink.

Coccinea speciosa: orange-red.

Josephine Klinger: crimson.

Nancy Waterer: golden yellow.

Narcissiflora: pale yellow. Double.

Sang de Gentbrugge: blood-red.

Unique: orange-yellow.

Ivnaphill azaleas flower about the same time as the Ghent hybrids, having a wide colour range and good autumn colouring of the foliage. Height about 4 ½ ft. Most of the following have some fragrance.

Eisenhower: orange-scarlet.

Harvest Moon: pale yellow.

H. Hunnewell: deep crimson.

Kathleen: salmon-pink with orange blotch.

Persil: white with yellow blotch.

Sandpiper: pale pink.

Satan: vivid scarlet.

Seville: rich orange.

Viscosepala: cream. Very fragrant.

Whitethroat: white. Double.

Exbury hybrids are probably the finest strain of all azaleas. Extra large flowers in shades of yellow, apricot, orange, flame, salmon, orange-red, cream and white. Mixed seedlings or named varieties are available. Aurora: salmon-pink with orange blotch. George Reynolds: deep yellow. Gibraltar: warm orange. Strawberry Ice: flesh-pink. Royal Lodge: deep red.

Dwarf evergreen azaleas (including the Kurume varieties) are often referred to as Japanese azaleas, since many varieties were raised in Japan.

The flowers are small but very freely produced so that the leaves are often completely hidden. They are very slow-growing, some varieties ultimately reaching 2 ft. after a number of years, others growing 1 to 2 ft. taller.

These azaleas are excellent rock garden plants. The colour range includes shades of pink, red, lilac, mauve, cream and white but no yellow. There is no fragrance. The flowering period is May and June, depending on variety.

Bengal Fire: brilliant fiery-red. About 3 ½ ft.

Gretchen: lilac-purple. About 4 ft.

Hinodigiri: bright crimson. About 2 ft.

Hinomayo: salmon-pink. About 5 ft.

Orange Beauty: orange-salmon. About 4 ft.

Palestrina: pure white with a faint ray of green. About 3 ½ ft.

Rasho Mon: scarlet. About 4 ft.

Seikai: white. About 2 ft.

Growing Azaleas Indoors:

Large numbers of Azalea indica (Rhododendron Sirnsii) varieties are imported annually from Belgium and Holland and bought by amateurs on seeing the colourful displays in florists’ windows. When brought into a living room they often fail to survive and it must be admitted that they are not the easiest of plants to manage, a greenhouse being desirable for best results.

If growing indoors place the pot in a sunny position and water as needed until June, taking care to remove all blooms directly they are finished. Plunge the pots outdoors in a cool, slightly shaded place (under a north wall is ideal). Do not allow the soil to dry out. Bring indoors before the first frost and treat as before. The plant may not flower again for a couple of years but if looked after carefully will often go on for many years. For greenhouse culture buy plants in 5 or 6 in. pots in autumn and grow in a temperature of 50 degrees F. to 55 degrees F. During the first season it is often better to let the plants grow naturally, with no attempt at early forcing. (Much better results are likely when forcing is deferred to the second and subsequent years.) Directly the flowers have faded re-pot in a peaty compost, and make this really firm. Syringe the plants with clear water occasionally and gradually harden off for planting outdoors in June. Bring into the greenhouse in October (temperature 45 degrees F. to 50 degrees F), and force into early bloom in the New Year (temperature about 45 degrees F.). Increase by cuttings of half-ripe wood in July, as with other types of dwarf azalea. Good varieties include the salmon Princess Beatrix, the brick-red Apollo and the cerise Ernest Thiers.

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