How to grow azaleas

Azaleas are acid-loving plants that require a pH of between 5.0 and 6.0. They only thrive in certain areas of the country, often where acid heathland thrives. 

As a result most gardeners need to grow them in containers full of ericaceous compost. Use rugged containers, such as oak half barrels or terracotta, and position them away from morning and full midday position so that their early flowers do not get frosted by a sudden thaw caused by sun.

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Azalea or rhododendron?

Azaleas are now officially listed under Rhododendron, but many nurseries still call them azaleas. Generally azaleas are smaller than rhododendrons, and they have finer foliage. 

Deciduous or evergreen azaleas?

There are two types of azaleas. Evergreen azaleas, sometimes called Japanese azaleas, are smaller and slower growing, reaching up to 3ft ( up to 90cm) after ten years. Evergreen azaleas are suitable for container growing, due to their size, or smaller gardens. Their small lance-shaped leaves often colour up in autumn.

Deciduous azaleas are taller and reach up to 5ft after ten years. They lose their leaves in the autumn, after colouring up well. Their flowers are often scented, but flower size varies, although many flower later extending the season. Deciduous azaleas are extremely hardy.

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Where to plant azaleas

Growing azaleas in the ground

Azaleas thrive in fertile acidic soil and they are easy to look after once they are established. Give them a generous mulch, between two and four inches deep, each spring to keep the soil moist and the roots cool. You could use pine needles, which help to keep the soil acidic, or top quality shredded bark or, best of all, home-produced leaf litter. 

In southern England azaleas will flower in more shade. However in other parts of the country give them a bright position or place them in part shade.

Growing azaleas in pots

Choose a wide, rugged container and stand it on pot feet to ensure good drainage. Use ericaceous compost, but try to find one with a loamy content and not too much peat, because loam-based composts hold nutrients and have a far better structure, making watering and feeding easier. 

Find a frost-free spot on the patio and water them regularly in summer, preferably with rainwater which is less alkaline than water from the tap. If tap water is the only water thing available, leave it to stand in the can for half a day so that any chlorine evaporates.

Deadheading azaleas

Deadhead spent and fading azalea flowers to encourage new growth and further flowering next year.

Feeding azaleas

Once flowering is over, feed plants with a slow release ericaceous plant food in March or April and then again in June - following the instructions.

Pruning azaleas

Prune lightly if needed, should your plants get straggly or out of shape, in May and June. Deciduous azaleas respond well to a severe haircut but evergreen azaleas ( which tend to be far more compact) should only be lightly pruned in most cases.

Yellowing leaves

If the azalea leaves turn yellow your soil is probably too alkaline. You have two options. You can lift your plant and pot them up into ericaceous compost, or you can use an iron-rich feed such as Maxicrop Seaweed plus Iron to create more acidic conditions. This will need to be applied regularly.

Moving azaleas

Transplant in spring or autumn if needed, lifting the plant carefully so that the rootball stays intact.

Good varieties of azaleas

Azalea Japonica ‘Arneson Gem’ (Deciduous Knaphill Hybrid)
Showy, large orange-yellow flowers in May and June on a compact plant. Good autumn foliage. 120-150cm in 10 years.

Azalea Japonica ‘Blue Danube’ (Evergreen)
An old and very hardy May-flowering variety with large, violet-blue flowers spotted in purple-red. Upright spreading habit reaching only 60-80cm in 10 years.

Azalea Japonica ‘Maruschka’ (Evergreen)
Carmine-red flowers in mid-May, held above dark-green foliage that turns a wonderful bronze in winter. Height 40cm and spread 60cm in 10 years.

Azalea Japonica ‘Johanna’ (Evergreen)
One of the best azaleas for autumn foliage, with dark shiny leaves turning dark red as winter approaches. Large, pink-toned carmine red flowers in May. Height 75-90cm in 10 years.

Azalea Japonica ‘Orange King’ (Evergreen)
Sun-shot, coral-pink to orange flowers, speckled with dark freckles, on this May-flowering azalea. Height 50-75cm in 10 years.

Azalea Japonica 'Orange Beauty' (Evergreen)
Bright orange/salmon blooms with glossy foliage. Height up to 80cm in 10 years.

Azalea Japonica ‘Squirrel’ (Evergreen)
A late-flowering Scottish variety for June, with bright-scarlet flowers on a compact plant. Height 40-60cm in 10 years.

Azalea Japonica 'Mother's Day' (Evergreen)
Vibrant red flowers the bloom in April and May. 60-90cm in 10 years.

Azalea Japonica 'Sir Robert' (Evergreen)
A beautiful azalea with white/pink streaked leaves. Up to 80cm in 10 years.

Azalea Japonica 'Hotshot Variegata' (Evergreen)
A scarlet variety with evergreen variegated green and white foliage. It can be grown in containers or in borders and prefers full sun to partial shade. Can grow up to 1m in 10 years.

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