Growing Azaleas on the east coast of Australia
Introduction
The following information concerns growing Azaleas in the Southern hemisphere, in particular, the east coast of Australia. It should be noted that the Azaleas mentioned are all evergreen Azaleas the deciduous varieties not being suitable for the temperate climate of Australia's east coast although many Mollis and Exbury hybrids do quite well in the more elevated areas of the Great Dividing Range.
Those people of the northern hemisphere reading this will notice quite a diference in the way Azaleas are grown in Australia. This is due to both the moderate climate and the soil type, most coastal Australian soils being very poor in nutrients and quite low in pH.
For the Australians reading this, Azaleas are a lot hardier than most people think. If you treat Azaleas the same way you would grow an Australian native plant, they will thrive much better than if you treat them too gently.
I hope you find the following information useful and please do not hesitate to email me with any comments about this site.
Adrian Frood
Azaleas are a part of the Rhododendron genus. It was originally thought that all Azaleas were deciduous and all Rhododendrons were evergreen until the discovery of evergreen Azaleas in Asia, so that started to confuse things a little with the botanists. Azaleas started out about 70,000,000 years ago as a form of magnolia, to which they are related, and evolved to an advanced form of heath. These plants are all part of the same Family (ericaceae). Most plants are named using Greek or Latin words which relate to the plant in some way, e.g. Spirea (may bush) is Greek for wreath. Azalea, in Greek means dry or parched. This is because in their native habitat, they live on very poor soils usually in mountain areas. The Japanese have been growing Azaleas for more than 400 years and this is where the Kurume type Azaleas have come from. In the early 19th century, a baker in Ghent in Belgium began to hybridise Azaleas by crossing Rhododendron luteum with American Azaleas to produce the Ghent hybrids. These are deciduous Azaleas that are virtually impossible to grow here. Other growers in the same town began to cross the evergreen Asian Azaleas (Rhododendron indicum) to produce an Azalea much like the ones we see today.
They were not cold-hardy plants and had to be grown as indoor plants or in greenhouses in Europe. These were known as Belgian-Indian Azaleas and were exported to America where they developed what are known as the Southern-Indica Azaleas. All the common Azaleas we see today have been bred from these plants. So, the Azalea we know in Australia is not really a cold-climate plant at all, but a plant that is quite suited to our environment. The problems encountered with non-hardy Azaleas is because of modern breeding practices more than anything else. Many plant breeders are more intent on producing quality flowers than quality plants which has put a lot of very pretty looking Azaleas on the market but they may be very susceptible to things like root-rot and other fungal diseases. A good example of this is Silver Anniversary. A very nice looking Azalea but virtually impossible to grow in the ground because it is prone to root rot, it will grow much better in a pot in well drained potting mix.
I have already touched on some of these already, but the main types of evergreen Azaleas are;
The hardiest of these varieties are the Belgian-Indian and Tall Single Indica. Some of the Kurumes are quite hardy, but you need to be careful which ones you grow. Satsuki and Gumpo are reasonably hardy plants but they flower too late in the season and the flowers can be affected by hot weather. The Southern Indicas are the old style, tall single flowered varieties most of us know such as Alba Magna, Magnifica and Exquisite. They are very hardy and grow in the full sun or semi-shade. The Belgian-Indian hybrids are only not hardy for the reasons I stated earlier and, depending on from what they have been bred, can be shade only or sun-tolerant Azaleas. It makes no difference what colour the flower is or whether it is single or double, it is just a matter of breeding.
- Belgian-Indian
- Tall Single (Southern) Indica
- Kurume
- Satsuki
- Gumpo
There are 6 main flower types in Azaleas, they are;
It can be quite difficult to differentiate between these different types at times, so this is a rough guide only. One plant can have some double and some semi-double plants at the same time so it is not a black and white segregation but just a way of classifying different types of flower.
- Single
- Single hose-in-hose
- Semi-double
- Semi-double hose-in-hose
- Double
- Double hose-in-hose
Azaleas as a whole get very few pests and diseases. Some of the most common pests are, Lace Wing, Red Spider and occasionally Grass hoppers. Lace Wing is best controlled by a systemic insecticide such as Rogor 40 this will also control Red Spider, but because it is a mite and not an insect, a miticide is preferable. Grass hoppers can be simply squashed if there aren't too many of them, or any insecticide will take care of them. The main diseases are Petal Blight, a fungal disease which attacks the flowers of Azaleas. It usually occurs during warm, humid weather and makes the flowers go mushy and stick to the plant. One way of preventing this is to not water at night and to pick off and burn any infected flowers. It can be treated with a fungicide called Bayleton, to prevent the onset of Petal Blight, you need to spray about every two weeks during the main flowering period. Another fungal disease is one called Leaf Gall and is reasonably uncommon and not very harmful. Symptoms are swelling of new growth and the best treatment is to pick off the infected part of the plant and burn it. Root rot is the biggest killer of Azaleas. It is a fungal disease which attacks the roots and ultimately kills the plant. The best cure is to prevent it occurring by making sure the Azaleas have adequate drainage. All Azaleas need an open, well drained soil or potting mix.
Azaleas do not need a lot of fertiliser. The best thing is to treat them like a native. If you grow them in the ground, just give them a good quality blood and bone maybe twice a year or if you have them in pots, a slow releases fertiliser such as Osmocote. Once again, use a native preparation and the longer lasting one, usually 8 to 9 months. Make sure the plants are well watered before fertilising and in hot weather, don't let them dry out after fertilising. Because Azaleas have roots close to the surface, mulch the plants well to keep moisture in and the roots cool in the Summer. It also keeps the weeds down so the plants won't have to compete for water and nutrients.
Because Azaleas grow in low pH soils naturally, they have adapted to this, and high levels of some nutrients such as calcium, magnesium and potassium can be harmful to them. Azaleas prefer a soil pH level of between 4.5 and 5.5. At levels above or below this some nutrients become unavailable or at levels which may be toxic to the plant.
© 2009 Adrian Frood
