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Rhododendron
Rhododendrons are magnificent shrubs ranging from alpine kinds to enormous trees with leaves up to 90cm (3ft) long. They form great blocks of colour as branches become obscured by a profusion of beautiful flowers.
The only areas where rhododendrons don't occur in the wild are Africa and South America. They've been grown in Britain since the 18th century, but it wasn't until the 1900s that they became widely known. The start of the 20th century saw a flood of new species introduced by plant hunters, while over the past few decades most of the breeding has been done in north America and Germany.
The latter has produced plants better suited to the UK climate and smaller gardens, as they grow about 1.2m (4ft) high after ten to 15 years, and also flower from a young age. Two of the best include R . 'Fantastica' and 'Hachmann's Polaris'.
There are more than 900 species and 8,000 varieties of rhododendron, the latter being preferred by gardeners. Hybrids bred from the dwarf R. yakushimanum are known as yaks. There are also many dwarf rhododendrons that are perfect for smaller gardens.
The girth of big rhododendrons is roughly the same as the height, so make sure you have enough room.
This dwarf form has creamy-coloured blooms, unlike most of the other members of the species, which have pink flowers.
These rhododendrons are attractive even when not in flower and are ideal in smallish gardens.
This dwarf species and its hybrids have an attractive, compact habit that looks good all year, with leathery leaves like downward-pointing spoons and mid-spring, porcelain-like flowers in a range of colours. After flowering, new shoots are covered in a felt-like, white woolly covering.
The species was introduced to Britain in 1934 from Yakushima Island, off Japan. There it grows on cool, windswept mountains, but it can tolerate sunnier sites.
These free-flowering shrubs are closely related to rhododendrons but are generally smaller. Most reach about 90cm (3ft) high and are best grown in a sunny spot, where they produce blooms in late May to early July.
Rhododendrons and azaleas like dappled shade in a sheltered position, away from cold winds. They also need an acid soil of pH5 or less.
A simple pH testing kit will indicate whether your garden soil is acidic. If the soil pH level is higher, around pH6, it's still possible to grow rhododendrons in the open ground provided they're treated with an appropriate acidifier to prevent the leaves from turning yellow and the plant becoming sickly.
Dig in plenty of organic matter, such as well-rotted manure, before planting to improve the soil. Never use mushroom compost as it can contain lime and have a high pH level.
In gardens where the pH level is higher than six, it's best to grow rhododendrons in raised beds or containers filled with free-draining ericaceous compost. If made with bricks, the bed should also be lined with polythene to prevent lime from the mortar leaching into the soil and making it alkaline.
When using a container, choose a wide, deep one, such as a half-barrel. Keep the plants well watered, especially during summer when the following year's flower buds are forming. Use rainwater, as tap water often has a very high pH level. Also keep the compost moist in summer, and don't let it become waterlogged in winter.
Rhododendrons have shallow roots, so it's important to plant them at the same depth as they were growing in the pot. Also avoid hoeing or forking around them so you don't disturb the roots.
To keep down weeds, put in ground-cover plants such as hostas and Geranium macrorrhizum , which will form a thick carpet of leaves and flowers.
Once planted, rhododendrons need very little attention and, if grown in ideal conditions, there's no need to feed or prune.
Deadheading after flowering improves growth as it directs the plant's energy into the formation of new flower buds. (Take care not to snap off the dormant buds that lie beneath the flowers.)
Spring and autumn are the best times for planting yaks. They tolerate more sunlight than most varieties and will even grow in moderately exposed positions, providing they've had a chance to establish and don't dry out.
Mulch around the plant's base to retain moisture, keep down weeds and add nutrients.
Rhododendrons are prone to a variety of problems, but if grown under the correct conditions will succeed.
Look out for powdery mildew, which is indicated by blotches of a white powdery deposit on the underside of the leaves, with corresponding pale patches usually on the upper side. A bad attack can cause defoliation, although most plants will send up fresh shoots the following spring. Yaks are less prone to this than other varieties. If necessary, spray with a fungicide about once a month from spring to autumn.
Look out for vine weevils in container-grown plants. The adult beetles merely cause notching on the leaf edges, but the grubs munch through plant roots, which can result in the whole plant collapsing due to an inadequate support system. Protect against attacks using a biological solution that can be watered.
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