The 19th century brought technological change and impressive engineering feats. It also brought a new class of wealthy industrialists who competed fiercely for unusual and exotic plants for their gardens and greenhouses.

It was their money that funded the intrepid plant hunters who returned from the East with new species beyond the wildest dreams of gardeners of the day. Until then, the rhododendron had attracted little interest in the West, but each expedition brought a range of new colours, forms and fragrances, paving the way for the thousands of hybrids that include some of the most spectacular flowers and superb foliage known to horticulture today.

The splendour of these impressive plants belies the fact that they can be remarkably easy to grow and maintain.

'True' rhododendrons

'Earl of Athlone'	'Australian Sunrise'	'Gothenburg'

Most of us associate the plants known as rhododendrons with the big, broad-leaved shrubs laden with traffic-stopping trusses of showy springtime flowers.

There is an enormous variety of rhododendron forms. At one extreme are tiny miniatures and ground-hugging prostrates suitable for the rock garden, such as Rhododendron trichostomum with its twiggy shrubs and the Burmese R. forrestii. At the other end of the scale are forest trees which include R. arboreum and the largest of the genus, R. sinogrande, whose massive leaves can reach over 1 m (3 ft) in length.

Most of these cool-climate evergreen species with their colourful blooms are found in the Himalayas, southwestern China and northern Myanmar, giving rise to the term 'Asiatics', but others are also scattered across northern Asia, Europe and North America.

Vireya rhododendrons

Rhododendron tuba	'Niugini Firebird'	'Nancy Miller Adler'

The vireya rhododendrons originate in cooler mountain forests, from southeast Asia to New Guinea, with two native to northeast Queensland. These high-altitude plants are becoming popular as new hybrids have greatly improved their habit and floral abundance.

Despite their tropical origins, vireyas can be grown as far south as Tasmania, as long as they can be protected from frost - plant them under evergreen trees or under the eaves of a building.

Many vireya species are tree-dwelling epiphytes, which make them ideal for growing in hanging baskets.

Cool, colourful azaleas

Rhododendron occidentale	'Gretel'	'Kelly's Cerise'

Once classed as a distinct genus, azalea is simply a compact rhododendron, usually with five stamens instead of the 10 of other rhododendrons.

Cultivated in Japan for centuries, evergreen azaleas became very popular in the northern hemisphere as Christmas-flowering house plants. There are varieties that can be grown in gardens from latitudes as far as Tasmania, northward into the subtropics.

Deciduous azaleas are a bonus for cooler areas, bursting into masses of brilliant yellow, orange, red or white flowers, often before their spring foliage emerges. Their leaves progress from the bright green of spring, shading to bronze over summer, before a final blaze of autumn colour.

Growing tips

• Many varieties will tolerate full sun, but most prefer some shade and protection from wind. Most varieties, except vireyas, will tolerate frost.
• Plants enjoy a freely draining, acidic soil with a pH level between 4.5 and 5.5. Improve soils by adding organic matter such as compost.
• Never allow the soil to fully dry out. Mulch deeply around plants and install irrigation in drier areas.
• Feed plants in late winter or early spring with slow-release fertiliser peilets, or by top-dressing with blood and bone and well-decayed compost, coconut fibre, rice hulls or leaf mould.
• Deadhead flowers to encourage a bushier habit in young plants.
• Rhododendrons can live for many years in containers, a smart option for growers with difficult soils. There are specialised mixes available, but a freely draining, general-purpose potting mix will do the job.
• Plants in containers need extra watering. Water-retaining crystals will help keep the potting mix moist and plants growing together can be watered reliably by drip irrigation.
• Most of the few problems that afflict rhododendrons can be solved by improving growing conditions rather than by chemical means

Some specialist rhododendron suppliers in Australia

• Camellia Grove Nursery, Cattai Ridge Road, Glenorie, NSW 2157. (02) 9652 1200.
• Dicksonia Rare Plants, 686 Mount Macedon Road, Mount Macedon, Vic. 3441. (03) 5426 3075.
• The National Rhododendron Gardens, The Georgian Road, Olinda, Vic. 3788. (03) 9751 1980.
• Vireya Valley Nursery, Woori-Yallock Road RSD, Cockatoo, Vic. 3781. (03) 5968 8676.