Rhododendrons and Azaleas are amongst our best-loved garden plants. Each spring, these popular shrubs put on a spectacular and long-lasting display of colourful flowers. For flower to leaf ratio, it is difficult to think of plants that perform any better than Rhodos and Azaleas.
 
 
Azalea Hino de Giri
Although they’re most commonly seen in cool climate and temperate gardens; choose the right varieties and you can grow them in warm, humid climates as well. There are rhododendrons that occur naturally in the snow-covered Himalayas, and others from tropical south east Asia; there is even one that is native to the tropical rainforests of Australia.

There are several hundred species of Rhododendrons, and literally thousands of cultivars. There are both deciduous and evergreen types, and their size can vary from dwarf shrubs of 0.5 metre tall to trees over 20 metres in height.

What are Azaleas?

Rhododendrons and Azaleas are very similar plants, both belonging to the family Ericaceae, in the genus Rhododendron.
Most of the commonly cultivated Rhododendrons are hybrids. This means they have been produced by crossing two different species together.
Azaleas are hybrids which are produced mostly from four Rhododendron species (and occasionally others).

Azaleas are generally classified into the following 3 types:
  1. Mollis azaleas – deciduous types; best for cool, rich soil.
  2. Indica azaleas – have more showy and larger flowers.
  3. Kurume azaleas – have smaller less showy flowers (but often a greater number of individual flowers).
What to grow in the tropics?

The tropical rhododendrons are classified as Vireyas. Most of these are relatively small (some less than 1m tall, others perhaps to 2m). An Australian species, Rhodendron lochae, is native to North Queensland.
 
 
What to grow in the Sub-Tropics?

As well as the Vireyas, Indica type azaleas will grow well in the sub tropics.
 
 
What to grow in Temperate Climates?
  • Mollis, indica and kurume Azaleas.
  • Many larger Rhodos and rock Rhodos.
  • Vireyas are more difficult and slower to grow but can still be grown in a protected position such as a greenhouse or under the canopy of trees.
 
Rhododendron Talleyrand 
 
Growing Rhododendrons and Azaleas

In general, Rhodos and Azaleas will do best with:
  • Acid soil (generally pH 5.5 – 6)
  • Good drainage but also a moist soil.
  • Ideally soil which is rich in organic matter. Mulching is beneficial.
  • Protection from extreme heat. Semi-shade is ideal. Be aware that if planted under deciduous trees, the fibrous root system of the tree can compete with the rhododendron for moisture and nutrients. If the situation is too dark, the plant can become leggy and may not flower well. Some azaleas are labeled as ‘sun hardy’ but even these prefer semi-shade.
  • Avoid digging around the Rhodo as they have shallow roots which can be disturbed.
  • Pruning –
    • remove dead flowers and dead wood regularly.
    • Light shearing after flowering will keep them in shape.
    • Heavy cutting is tolerated but this is generally only carried out to reshape or rejuvenate the plant.
  • Feeding –
    • Rhodos respond to regular feeding
    • Ideally well rotted animal manure.
  • The most cold-hardy azaleas are the deciduous Mollis varieties.
  • Rhodos need shelter from strong wind.
TIP

Some Rhododendrons are fragrant. Check the label before buying.
 
 
Rhododendron fragrans
 

Places to Visit

  • The Rhododendron Garden, Olinda, in the Dandenong Ranges of Victoria, Australia.
    Probably the best public Rhodo garden in Australia.
    For more information, go to their website.
  • Pukeiti Garden, near New Plymouth, New Zealand
    The largest collection in NZ – something in flower all year round.
    Visit their website.
AZALEA AND RHODODENDRON CORRESPONDENCE COURSE

Australian Correspondence Schools offers a course on Azaleas and Rhododendrons. This course can be undertaken from any country in the world.
For more information, go to http://www.acsgarden.com/courses/azaleas-and-rhododendrons-541.aspx

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