Name: Azalea, evergreen azalea, deciduous azalea, Rhododendron cultivars.
Height: deciduous: usually 1–3m; evergreen: from 30cm to 3 m.
Foliage: deciduous or evergreen, depending on the species or cultivar.
Climate: deciduous azaleas require a cool temperate climate; evergreen azaleas can be grown in both cool and warm temperate climates.
Soil: a well-drained, rich organic acidic soil is required.
Position: most azaleas grow best in partial shade with protection from hot drying winds. Deciduous azaleas will grow in full sun in cooler areas.
Flowering and fruiting: colourful single or double trumpet-shaped flowers cover the shrub in spring.
Feeding: use a controlled-release fertiliser specifically for an azalea and other acid-loving plants. Apply after flowering and again in late summer/early autumn.
Watering: regular watering two to three times per week is required throughout the hotter summer months, as the azalea has shallow fibrous root systems.
Azalea is a type of rhododendron. It can be either deciduous or evergreen, depending on the species, and is usually covered in masses of colourful blooms in late winter or spring. Size ranges from 30cm tall miniatures that make the perfect centrepiece for the dining room table to 3m tall shrubs suitable for the back of the border. Many species grow much wider than their overall height.
The deciduous azalea originates from cooler parts of the Northern Hemisphere, including Europe, Japan, China and North America. It forms multi-stemmed shrubs with trumpet-shaped flowers in shades of yellow, orange, red, pink, lavender and white. Some also develop colourful autumn foliage. The deciduous azalea is best grown in cooler temperate areas of Australia and New Zealand with cold winters, and should be positioned in full sun or partial shade with protection from drying winds. Groups include the mollis, Ghent, Exbury and Knap Hill hybrids.
The evergreen azalea is mainly a hybrid of low-growing and compact species from China, Japan, Taiwan and Korea. It grows in warmer temperate climates with mild winters, where frosts are light. Some varieties can even be grown inside for a short period of time. Well-known hybrids include the Indica, Kurume, Kaempferi and Satsuki groups. The evergreen azalea prefers partial shade, but some varieties will take full sun in warmer areas with adequate water during the hotter months. Many of these can be successfully grown in pots and containers for many years.
The most important aspect of growing an azalea is the soil. Put some effort in at planting and you will be rewarded for many years to come. Azalea has shallow fibrous roots, so needs a rich organic acidic soil that is moisture retentive, but also well drained. Azalea grows best in a soil pH between 4.5 and 5.8, so test your soil first with a pH kit. Always mix in some sphagnum moss peat, compost and pine bark at planting to acidify the soil and lower the pH, and apply a pine bark mulch to keep the shallow roots cool during the summer months. Granulated or liquid sulphur can also be used to lower the pH on alkaline soils. In pots and containers, always use a premium standard potting mix for azaleas, gardenias and camellias, and keep them well watered throughout summer.
Choose a fertiliser specifically for acid-loving plants like azaleas, gardenias and camellias to avoid the possibility of burning from conventional fertilisers. Always apply after flowering in spring and again in late summer/early autumn to avoid surge growth covering the flowers.
Azalea responds well to pruning straight after flowering. A deciduous azalea requires little pruning apart from the removal of old declining wood. An evergreen azalea is naturally compact, so only needs dead branches removed, or to be trimmed to the desired shape. It looks amazing trimmed into balls, domes and organic shapes underneath tree canopies, and also makes an excellent bonsai specimen. Any overgrown or straggly plants can also be cut back hard at this time.
The two major problems affecting an azalea are azalea lace bug and petal blight.
Azalea lace bugs are found on the undersides of the leaves, causing silvery mottling of the foliage and decreased vigour. Treat at the first sign with insecticidal soap sprays, horticultural oil or Neem oil.
Petal blight usually occurs when there is cool wet weather or overhead watering during flowering. This causes the flowers to become spotted. These brown spots spread and merge, becoming limp and slimy.
These flowers may remain stuck to the foliage for many weeks. Pick off dead flowers in winter and apply a preventative spray from just before the buds colour up until after flowering.
An evergreen azalea can be easily propagated by taking cuttings during summer and early autumn. Take cuttings of firm tip growth around 10cm long and place them in a pot with seed and cutting mix, or 50:50 peat and coarse propagating sand. Remove the bottom two-thirds of leaves and dip the bottom of the cutting in rooting hormone. Place in a propagator or a pot covered with a clear 2L bottle top and position in partial shade. In around 6–8 weeks the cuttings should have taken root.
A deciduous azalea is usually grown from seed sown on the surface of seed trays in late autumn or early spring.
Camellia: a magnificent evergreen shrub flowering from late winter through to spring, suitable for acid soils.
Rhododendron: ranges from a small shrubs to a large tree with magnificent blooms in spring, also suitable for acid soils.
Hydrangea: deciduous and evergreen shrubs with large leaves and colourful conical, lacecap or mophead flowerheads.
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