RHODODENDRONS AND AZALEAS
Rhododendrons and azaleas are amongst our best-loved garden plants. Each spring, these popular shrubs put on a spectacular long-lasting display of colourful flowers. 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.
Check out our Azalea & Rhododendron Course
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 tall trees over 20 metres high.
Azaleas are actually a type of rhododendron; they are botanically the same group of plants.
TYPES OF RHODOS
Most of the commonly cultivated rhododendrons are hybrids.
TYPES OF AZALEAS
Azaleas are hybrids which are produced mostly from four rhododendron species (and occasionally others). Azaleas are generally classified into the following three types:
a) Mollis azaleas – deciduous types; best for cool, rich soil.
b) Indica azaleas – have more showy and larger flowers.
c) 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.
WHAT IS A HYBRID?
When two species are cross bred, a new type of plant is produced which shares the characteristics of both parents.
The following generalisations can be made about their requirements:
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 exceptionally 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.
Some rhododendrons are fragrant. Check the label before buying.
PLACES TO VISIT
The Rhododendron Garden, Olinda, in the Dandenong Ranges, Vic. Probably the best public rhodo garden in Australia.
Pukeiti Garden, near New Plymouth, New Zealand The largest collection in NZ – something in flower all year round.