Rhododendron Growing Tips
Common name: none
There are numerous rhododendrons that are capable, when in flower and when grown well, of stopping you in your tracks. They are available in a wide range of sizes, from large treelike specimens and larger shrubs, down to ground huggers that are suitable for the rock garden or front of a border. Many are grown for their rich vibrant colours, others are more subtle with pastel shades. Azaleas -one of the smaller-leaved forms of rhododendron – usually have the most brilliant coloured.
It is a huge family, with a considerable number of species and legions of named varieties, the results of many years of. Some are evergreen and some deciduous. Some have individual leaves the size of paddle blades, whilst the smallest is around I.5cm (3/4in). Some rhododendrons flower in early winter and are best grown in mild districts in sheltered spots. The majority bloom in the spring.
Rhododendrons are lime-haters and require acidconditions, so are not suitable for some districts. Where the soil itself is a problem, some of the more compact varieties can be grown in large containers in ericaceous compost, but ensure they do not become dry in hot weather.
Popular species and varieties
The large-flowered are among the most popular of all shrubs, and are readily found at garden centres. This in no way detracts from the charm of the species themselves. When it comes to choice it is difficult to know where to start. Among those with red blooms are ‘Baden Baden’, a good dwarf variety, and ‘Britannia’ (AGM), an old favourite. One very popular for smaller gardens is the bright orange-red ‘Dopey’ (AGM).
Always eye-catching are the yellows. Among the best are ‘Hotei’ (AGM), medium sized with masses of deep yellow bell-shaped blooms, and ‘Queen Elizabeth II’ (AGM), a free-flowering medium variety with greenish-yellow, wide, funnel-shaped blooms.
For white flowers there is ‘Helene Schiffner (AGM), an old stager but still among the best. The buds are mauve to start with, opening to reveal pure white flowers. One white was introduced as long ago as 1867: ‘Sappho’ (AGM). Here again the buds are mauve, but the pure white flowers have a rich purple blotch.
‘Percy Wiseman’ (AGM) is a compact plant with white flushed pink blooms; ‘Purple Splendour’ (AGM) is, as its name indicates, a rich deep purple, and ‘Morgenrot’ (AGM) is a lovely rose red.
Deciduous hybrid azaleas
Well known for their free-flowering habit and range of colours, the deciduous azaleas range in height from 1.5-2.5m (5-9ft). These also require acid soil conditions and preferably a sheltered spot in light shade. Among those to look for are the flame-orange ‘Gibralter’ (AGM), and ‘Glowing Embers’, best described as a reddish orange. ‘Satan’ (AGM) is a lovely geranium-red, and ‘Persil’ (AGM) has masses of white blooms with an orange-yellow flare.
Evergreen hybrid group
These are widely referred to as Japanese azaleas. They are excellent, low-growing shrubs ranging from 0.6-1.2m (2-4ft) in height, and are grown for their masses of late spring and early summer flowers. They often completely cover themselves with blooms so that the foliage is hidden. Two great favourites are the very dwarf ‘Hatsugiri’ (AGM), a striking magenta purple, and the taller ‘Hinomayo’ (AGM), a lovely clear pink. Equally as attractive are the rose-red ‘Mother’s Day’ (AGM), and the white ‘Palestrina’ (AGM). One you can hardly fail to miss for its sizeable bright red blooms is ‘Vuyk’s Scarlet’ (AGM). These azaleas provide a magnificent show when grouped together; sometimes colour clashes are thought to be desirable, but I try to avoid them.
Soil type Acid soil is essential; it should be moist but not. The ideal conditions are sandy loam, which does not dry out. Adding peat or leaf mould will help to retain moisture on lighter soils.
Planting Most rhododendrons, especially those with larger leaves, are best grown in a lightly shaded spot where they are not subjected to cold winds. Many will grow happily in full sun provided sufficient moisture is available at all times. Any that flower before the late spring should be positioned where the flowers are not in sunlight in the early morning, as after a frost these can be damaged. Planting can be carried out in the autumn or spring.
The rootball should be set just below soil level and topped with a mulch of peat or leaf mould. Ensure the plants are well watered, and keep the soil moist in dry weather.
Pruning Regularis not required, but any straggly growth can be removed in the spring. Dead-heading where possible, is an advantage but take care not to damage growth buds at the base of the flower.
Propagation Increasing rhododendrons takes quite a time. This is best done byor, in some cases, cuttings from those with small leaves. Unless you are skilled in the art of propagating rhododendrons, and have plenty of room and time, it is probably best to consider buying any new plants you require.
Pests and diseases One problem that can be encountered in unsuitable soils is yellowing of the leaves, which is known as chlorosis. Watering with a sequestered iron compound will help, but only temporarily if lime is present. There are a number of fungal diseases that can attack rhododendrons.