How to grow azaleas

Azaleas are closely related to rhododendrons. Once categorised as different species, both azaleas and rhododendrons are now placed together in the Rhododendron genus. They share many characteristics but there are some differences:

• Azaleas are always evergreen while rhododendrons are sometimes deciduous
• Azalea leaves are thin and often coated in fine hairs, while rhododendron leaves are usually thick and leathery
• Azalea flowers have five to six stamens, while rhododendron flowers typically have 10 or more stamens
• Azalea flowers appear in clusters of around three, at the end of a stem, while rhododendron flowers grow together in large 'trusses'
• Azaleas have more stems than rhododendrons

How to grow azaleas

Outside, grow azaleas in a sheltered spot in partial shade or full sun. Most varieties look best in a shaded or woodland border, or in pots.

Indoors, grow azaleas in a cool, well-ventilated spot, such as a conservatory, in bright light but not 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 that's wider than it's deep and back fill with leaf mould and 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, including indoor 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 outdoor azaleas in a sheltered spot in partial shade or full sun. Many cultivars suit planting at the edge of a woodland border or shady area. Smaller varieties look best at the front of a border, or in pots.

Indoors, grow azaleas in a well-ventilated room with dappled or indirect sunlight. Temperatures should be cool, around 16-18ºC 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 that's wider than it's deep and back fill with leaf mould and 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 weekly 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. A weak solution of black tea can also be good for azaleas, as it can increase the acidity of the compost. Deadhead spent blooms regularly to prolong flowering, and then keep in a cool room for the rest of the year. To instigate flowering the following summer, feed weekly, and repot as mentioned above. Then, in late autumn, move your azalea to a colder room (six to 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, taking cuttings is the best option. 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 rooting powder may increase your chances of success.

Growing azaleas: problem solving

Like rhododendrons, azaleas suffer 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 six to 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.

Azalea varieties to grow

• Rhododendron ‘Pleasant White’ – a dwarf, evergreen azalea with white flowers. It will suit a small garden, in a semi-shady 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 can be toxic to people and animals but is good for bees that love the nectar rich flowers.
• Azalea 'Rosebud' – a dwarf, 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 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.