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Easy Rhododendrons and Azaleas

While roses are considered by many gardeners to be the Queen of the garden, Rhododendrons are said to be the King.

While roses are considered by many gardeners to be the Queen of the garden, Rhododendrons are said to be the King.

The vivid displays produced by rhododendrons and azaleas can last for several months. There are plants to suit any garden — but to thrive they must have acid soil and good drainage.

Rhododendrons and azaleas are among the most decorative shrubs available for the home garden. Varying in size from mat‑like dwarf shrubs only a few centimetres high to trees higher than 7m, they can be planted in any size of garden and thrive in a variety of positions.

The Rhododendron gets its name from the Greek — rhodon (rose) and dendron (tree). The genus was officially established and named in 1753 by the Swedish botanist, Linnaeus. At the same time he created the separate genus of Azalea. In the 19th century another botanist, George Don, realised there was no botanical difference between Rhododendron and Azalea, and both species were classified in the genus Rhododendron. They remain so today, though gardeners still prefer to talk of rhododendrons and azaleas as two separate types of plants. Rhododendrons are mainly evergreen shrubs. Azalea mollis is deciduous, and two very popular groups, Rhododendron obtuseum and the Kurume azaleas, are both evergreens. Rhododendron indicum, the other variety grown extensively in South Africa, is also an evergreen, but has much smaller foliage.

The plants are mainly native to the northern hemisphere, although some species do occur in Malaysia and New Guinea, and one rhododendron is native to the rain forests of northern Queensland. Botanists differ on the number of species, but it is thought to be in the region of one thousand.

The one thing that rhododendrons have in common is that, in nature, they are usually found from 1000m to as high as 5 500m above sea level. The greatest number of species occur in India, Burma and China, at the eastern end of the Himalayan mountain range. Rhododendrons also occur in Japan, the USA, parts of Europe, and one hardy species, a low‑growing shrub which flourishes in the tundra, follows the Arctic Circle from Siberia to Greenland.

The flowers of rhododendrons and azaleas have a wide range of colour: white, pink, lavender, violet, purple, yellow, crimson, scarlet and orange. The shapes of the flowers range through tubular, starry, funnel, bowl and bell‑shaped, varying in size from 2‑15 cm wide and 2‑10cm long.

In the past, the rhododendron was often regarded only as a cool climate plant, and the development of new varieties was carried out mainly in the northern hemisphere. The tendency was to encourage late flowering to avoid frosts.

Over the last 25 years, however, breeders in Australia and New Zealand have successfully encouraged early flowering to avoid the heat of the summer. A number of varieties which reach their flowering peak between late winter and mid‑spring are now available. These early flowering varieties should have a much longer flowering period than the older types of rhododendron, and are suitable for all areas except those subject to late frosts. In the future, tropical species may be used to produce rhododendron hybrids well suited to humid coastal areas.

The Indica azaleas, a popular group derived from the Rhododendron indicum and Rhododendron simsii species, can be grown over a much wider climatic range than most other types. Deciduous azaleas, as well as the small-flowered Kurume varieties, are better suited to cooler climates.

Although the majority of rhododendrons are cool climate plants, many of them grow quite well in temperate coastal regions. It is worth remembering that those described as ‘tender’ in European or North American books or catalogues are more likely to be suitable for South Africa than the ‘hardy’ species.

Rhododendrons need to be grown in dappled or light shade. The soil should be moist and acid — the plants will not thrive in soil containing chalk or lime. Given the right conditions, a succession of varieties can be in flower for several months of the year.

Generally, the plants look their best in a natural or wilderness garden, where they are not restricted to the formal confines of beds and lawns.

The smaller rhododendrons and azaleas are most effective when used boldly in a mass planting. Kurume azaleas or deciduous azaleas should be planted in groups — either mixed or in one colour — for a brilliant display of blooms. The Kurume varieties make a splendid border for a path or driveway, while the deciduous azaleas are particularly attractive with a background of evergreen plants. Such a background shows up the warm autumn tints of the leaves borne by some deciduous varieties.

Many rhododendrons (particularly the larger varieties) are best planted with other plants to ensure the maximum effect during the long periods when evergreen rhododendrons are out of flower, and the deciduous kinds have not yet reached the autumn-colouring stage. The soil which suits rhododen­drons allows for a wide range of plants to be grown with them.

The larger flowered rhododendrons produce such a mass of colour that they should be planted in a very large garden; otherwise they are best used as accent plants among other shrubs and trees. They do not mix with dwarf conifers, but look well in a mixed border of assorted deciduous and evergreen shrubs and trees. Beware of dense‑growing trees which create too much shade, or those with powerful or very shallow root systems.

A massed planting of azaleas under a light canopy of deciduous trees, preferably with a tap root, will make for a very effective combination.

Camellias are also ideal for growing with rhododendrons. Low‑growing plants such as heath or heather, which thrive in acid soil, are also of ornamental value. You can grow many ground‑cover plants, or ferns with fine contrasting foliage, with rhododendrons to provide additional colour.

THE WIDE CHOICE FROM GIANTS TO DWARFS

Because rhododendrons and azaleas range in size from tree‑like giants to prostrate dwarfs, you should decide on the space you have to fill before buying your shrubs.

The size of the plants can vary considerably according to the climate of the area in which they are grown. The heights given here are average figures; in some areas the plants may grow smaller, in others where climate and other growing conditions are ideal, they may grow taller.

Tree‑like plants (over 4,5m) The biggest rhododendrons are evergreens which grow to 6m and more. They are suitable only for large gardens where their vigorous growth will not be restricted. Rhododendron ponticum does well in regions with mild winters. It has mauve flowers which appear in early to late spring.

Large bushes (2‑4,5m) Evergreens suited for smaller gardens include many varieties derived from Rhododendron indicum: ‘Magenta’ (deep magenta), ‘Grandiflora Alba’ (white), ‘Flambeau’ (brick red), ‘Stella’ (red), ‘Multiflora’ (salmon pink), ‘Reine de Pays Bas’ (rich violet‑pink with white margin).

Medium shrubs (1‑2,5m) The deciduous azaleas are all medium‑sized bushes, which make them popular in gardens of average size, but they do not do well in areas with hot summers and mild winters. The Exbury hybrids give a wide range of colours, from yellow to delicate pinks.

Small bushes (60cm‑1m) Two attractive Australian‑raised hybrids are ‘Little Girl’ (pale pink flowers) and ‘Only One Earth’ (cerise red flowers). Some favourites of the evergreen azaleas in this group are: ‘Claude Goyet’ (red, very large double), ‘Madame Moreau’ (double pink with frilly white margins), ‘Red Wing’ (cerise red), ‘Souvenir de Prince Albert’ (soft rose-pink, edged white), ‘Temperance’ (lilac mauve), ‘Violaceae’ (rich violet-purple). The evergreen azaleas of the Kurume or Indica groups are particularly suitable for small to medium‑sized gardens, and are well suited to warm climates. Both groups are commonly grown in temperate zones from humid coastal areas to the cooler highlands.

Indicas are usually large‑flowered varieties, while. the flower’s of Kurume azaleas are comparatively small. ‘Albert and Elizabeth’ (double white with a rose margin) and ‘Pink Pearl’ (double light pink) are popular Indica types. ‘Snowflake’ (white flowers) and ‘Coral Bells’ (pink flowers) are Kurume plants, and bear masses of blooms in mid‑ to late spring.

Dwarf bushes (30‑60cm) Dwarf evergreen hybrids, suitable for rock gardens, pots or tubs, include ‘Ambrosius’ (bright red flowers), ‘Gretel’ (silvery pink cyclamen edge) and ‘Madame Auguste Haerrens’ (soft pink‑edged white).

Watch for future posts which will deal with cultivation of, and care for Rhododendrons and Azaleas, as well as the pests and diseases that sometimes afflict these beautiful shrubs.