How to grow azaleas

Azaleas are perennial flowering shrubs, usually bearing flowers from March to June, depending on the variety. There are thousands of varieties to choose from, with flower colours ranging from pinks and purples to reds, oranges and yellows. Azaleas grow best in a semi-shaded bed or woodland border in the garden, but they also do well in pots. Some azaleas (sometimes known as greenhouse azaleas) are suitable for bringing into the home from a cool, protected environment as house plants, although they will suffer if kept in warm, dry conditions for too long.

Azaleas are closely related to rhododendrons and are placed together with them in the Rhododendron genus, which can make distinguishing between the two confusing when looking at a plant label. They share many characteristics but there are some differences you will notice with azaleas:

• Azaleas are usually deciduous, while rhododendrons are almost always evergreen
• The leaves of azaleas are thin, while rhododendron leaves are usually thick and leathery
• Flowers on azaleas usually have five stamens, while rhododendron flowers typically have 10 or more stamens
• Flowers appear on azaleas singly or in clusters of up to three at the end of a stem, while rhododendron flowers grow together in large trusses
• Azaleas have a large number of smaller stems, while rhododendrons have a smaller number of stout stems

How to grow azaleas

Outside, grow azaleas in a sheltered spot. Most varieties will be at their best in a semi-shaded or woodland border, or in pots of ericaceous compost in partial shade.

Indoors, grow azaleas in a cool, well-ventilated spot such as a conservatory in bright light but not too much direct sunlight.

All azaleas require humus-rich, neutral to acidic soil that's moist but well-drained. Use a test kit to measure the pH of your soil or look at neighbouring gardens to see if azaleas or other acid-loving plants are growing well in your area – avoid growing azaleas if you have an alkaline soil. Use peat-free ericaceous compost for azaleas in pots.

Azaleas are shallow-rooted plants, so make sure the rootball sits just below the surface. Dig a hole wider than it is deep and backfill with soil mixed with a little leaf mould or peat-free ericaceous compost. Water well.

Mulch azaleas annually with an acidic mix of leaf mould, peat-free ericaceous compost or conifer bark chippings. For pot-grown azaleas, replace the top layer of compost, or repot completely in spring and feed with an ericaceous fertiliser. Water with rainwater as much as possible – tap water might be too alkaline. There should be little or no need to prune.

While unlikely, if ingested by pets, all parts of azaleas and rhododendrons cause nausea, vomiting, depression, difficulty breathing and even coma. They can be fatal to dogs if eaten in large enough quantities.

In this short video guide, the experts at Burncoose Nurseries share their top tips for growing azaleas, including where to plant them and how to rejuvenate an old azalea.

More on growing azaleas:

• Alternative Christmas house plants
• How to grow rhododendrons
• Plants toxic to dogs

Where to plant azaleas

Grow azaleas in a sheltered spot in partial shade. Many cultivars suit planting at the edge of a woodland border. Smaller varieties look best at the front of a border, or in pots.

Indoors, grow azaleas in a well-ventilated, bright spot away from too much direct sunlight. Temperatures should be cool – around 13-16ºC is ideal.

How to plant azaleas

Like rhododendrons, azaleas require humus-rich, neutral to acidic soil that's moist but well-drained. Use peat-free ericaceous compost for pot-grown azaleas. The best times to plant azaleas are spring and autumn. They're shallow-rooted plants, so make sure the rootball sits just below the surface. Dig a hole wider than it is deep and backfill with soil mixed with a little leaf mould or peat-free ericaceous compost. Water well, ideally with rainwater.

How to care for azaleas

Mulch outdoor azaleas annually with an acidic mix of leaf mould or conifer bark chippings. For pot-grown and indoor azaleas, replace the top layer of compost, or repot completely in early spring and feed every couple of weeks with an ericaceous fertiliser. Try to keep the compost moist, but use rainwater as much as possible – tap water may be too alkaline. There should be little or no need to prune, but deadheading will improve the look of your azalea, while also encouraging it to bloom for longer.

Pot-grown azaleas are often gifted as house plants at Christmas. These have been forced to flower out of season and, as such, may be tricky to look after. For best results, keep the compost moist – sitting the pot in a larger container of water for several minutes once a week can be useful. Some people also give their azaleas the occasional weak solution of black tea to increase the acidity of the compost. Deadhead spent blooms regularly to prolong flowering, and then keep in a cool room, conservatory or porch for the rest of the year. To instigate flowering the following summer, feed every week or so and repot as mentioned above. Then, in late autumn, move your azalea to a colder room (6-10ºC), returning it to a cool, bright room (16-18ºC) in spring. With luck, your azalea should flower again.

How to propagate azaleas

Species azaleas can be grown from seed, but to propagate cultivars it is necessary to take cuttings. Take semi-ripe heel cuttings from mid to late summer, pushing them into a pot of gritty ericaceous compost. Cover with a plastic bag or propagator lid and remove this when the cuttings show signs of growth. Using fresh rooting powder may increase your chances of success.

Growing azaleas: problem solving

Like rhododendrons, azaleas suffer relatively few problems. Azaleas grown as house plants can fail to flower the following year, but this can be remedied by instigating a dormant period in winter. Simply move your azalea to a cold room of around 6-10ºC in late autumn. Then, in late winter, move it back to a spot where the ambient temperature is 16-18ºC, and your azalea should flower again.

Another common problem with azaleas comes from being in too much direct sunlight or wind, which can dry the plant out and scorch the leaves. If this is the case simply replant to a more shaded location.

Azalea varieties to grow

• Rhododendron ‘Pleasant White’ – a dwarf, evergreen azalea with white flowers. It will suit a small garden, in a semi-shaded border, or can be grown in containers.
• Rhododendron luteum - also known as Azalea pontica, this is a bushy, upright shrub with fragrant yellow flowers and good autumn colour. It is toxic to people and animals but is good for bees, which love the nectar-rich flowers.
• Azalea 'Rosebud' – a compact evergreen azalea, bearing masses of double, pink flowers, over small, mid-green leaves.
• Azalea 'Cannon's Double' – a bushy, upright, deciduous azalea, bearing large trusses of fully double orange-and-cream blooms, opening from pink buds. These contrast beautifully with the dark green leaves. It’s perfect for growing in a mixed herbaceous border or pot, and requires very little maintenance.
• Azalea 'Fireball' – a medium-sized azalea with bright orange-red flowers with a delicate fragrance. Its leaves emerge bronze-red, maturing to mid green, and then develop incredible autumn colour.