Rhododendron: Growing Guide

An important genus of garden plants, also including azaleas.

Situation:

Evergreen rhododendrons require a sheltered position which may be quite shady. There are now dwarf forms, quite suitable for small gardens. Azaleas never grow very large; there are deciduous as well as evergreen types in beautiful colours. Provide partial shade.

Soil:

In the right kind of soil success is guaranteed, but the soil must definitely be acid and rich in humus. If you are in doubt about your garden soil it is advisable to have the earth removed to a depth of 40 cm and to fill the hole with conifer-needle soil mixed with some rotted cow manure, always keeping the soil adequately damp. Chopped turves or peat are suitable alternatives. Culture Always remove faded flowers. Provide an annual feed of lime-free fertiliser . Only prune where absolutely necessary. Always buy your plants from reliable growers.

Propagation:

Growers propagate their rhododendrons by grafting or from cuttings. For amateur gardeners it is easier to increase the plant by layering. Rooting takes a very long time.

Rhododendron species and hybrids, evergreen

Rhododendron augustinii: Height to 1 m; lavender-blue to violet-coloured flowers with a yellow blotch in mid to late spring. The oblong leaves are scaly on the reverse. ‘Blue Diamond’ and ‘Blue Tit’ are two beautiful strains. Rhododendron catawhiense: Height to 3 m; very coarse, robust shrub with convex leaves; lilac flowers in late spring or early summer. Only suitable for parks or rough places.

Rhododendron hybrids: These are the fairly large garden shrubs often found in old parks and which, in the course of time, grow to 2-3 m in height and frequently more than that across; however they may be kept compact by pruning. Their flowering season is in late spring and early summer. A number of fine strains are: ‘America’, red; ‘Belle Heller’, white; ‘Cosmopolitan’, rose red; ‘General Eisenhower’, deep carmine-red; ‘Gomer Waterer’, very pale lilac; ‘Hollandia’, carmine red; ‘Peter Koster’, pale red; ‘Nova Zembla’, clear red; ‘Dr V. H. Rutgers’, dark red; ‘Scintillation’, bright pink; ‘Van Weerden Poelman’, red. All these strains are quite winter-hardy. Yellow- ‘”¦ flowering strains are sensitive to frost.

Rhododendron impeditum: Height 30 cm, bright purple-blue flowers in late spring; tiny leaves. Excellent for heather gardens, rock gardens, wherever there is limited space.

Rhododendron X praecox: Height 1.5 m; lilac-pink flowers in early to mid spring. Sometimes damaged by night frost, but very successful in small gardens. Rhododendron repens hybrids: Height to 1.5 m; an important group of small garden hybrids, early flowering, from mid spring onwards. ‘Baden Baden’, scarlet; ‘Carmen’, dark red; ‘Elizabeth Hobbie’, bright red; ‘Fruhlingszauber’, dark red; ‘Jewel’, deep scarlet; ‘Salute’, bright red; and ‘Scarlet Wonder’, luminous red. Unfortunately the colour scale is somewhat limited. Rhododendron williamsianum hybrids: Height 1.5 m; flowering season mid spring to early summer. Beautiful little spherical shrubs with broad oval leaves and clusters of large, bell-shaped flowers and ideal for the small garden; the colours are finer than those of the repens hybrids. ‘April Glow’, rose red; ‘Bow Bells’, soft coral-pink; ‘Karin’, deep pink; ‘Linda’, rose red; ‘Tibet’, white. Azaleas, main groups

Japanese azalea: Height 50-150 cm, spreading habit, partially evergreen; flowering season from late spring onwards, depending on the strain. There are large-flowered and small-flowered forms in the colours white, rose red, orange, carmine, purple red etc. Consult a comprehensive catalogue. This plant is also grown indoors.

Knap Hill-Exbury azaleas: Height to 2 m; deciduous, erect-growing shrubs; flowering season in late spring or early summer, depending on the strain. Flowers in particularly beautiful pastel shades – for instance soft yellow, orange, rose red, pale vermilion, white. Greatly recommended; quite winter-hardy.

Garden azaleas, also called mollis azaleas: Deciduous, height to 2 m; flowering season mid to late spring. Comparable to the previous group; here too, beautiful colours, shading from white and yellow to orange, salmon red and red. The flowers are lightly scented. Occidentale azaleas: Height 1 m; flowering season in very late spring. The flowers have a yellow blotch and are delightfully scented; usually pink or cream coloured. Very winter-hardy.

Other groups, such as Pontica hybrids and Rustica hybrids are now rarely available.

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