Azalea

Pink and Purple Azalea Flowers

Large group of evergreen and deciduous early flowering shrubs that are usually compact is size. There are two distinct types: evergreen Azaleas (or Japanese azaleas) and deciduous Azaleas. Both types are members of the Rhododendron family.

Family: Ericaceae (Heath Family)
Botanical Name: Azalea
Common Names:

Foliage: Simple green, deciduous or evergreen leaves. Deciduous forms often provide good autumn colour.

Flowers: Bell-shaped or tubular flowers. Often fragrant.

Flowering Period: Spring.

Soil: Moist but well-drained loam or sandy, acidic soil. Virtually all types are lime-haters.

Conditions: Sun or partial shade. Best grown in a north, east or west-facing aspect, in a sheltered location.

Habit: Bushy.

Type: Small shrub.

Hardiness: Hardy in most regions of the UK. Protect early flowering forms from late frosts.

Planting and Growing Azalea

Azaleas are not the easiest of plants to grow but are well worth the effort and very rewarding when in full bloom.

Plant in early autumn or in the spring, in a moist but well drained loam or sandy soil. Incorporate ericaceous compost into the soil at planting time. Water well and mulch after planting.

Most varieties make good container plants. Large leaf forms prefer light shade. Small-leaved forms thrive better in full sun.

Azaleas are not suitable for alkaline or chalky soils. The soil pH value should be below 7. Home use pH soil testing kits are available from most garden centres.

If your soil is alkaline (above pH 7) then container growing, using a good ericaceous compost, is one solution. It is possible to increase the acidity of soil by adding lots of organic matter and regularly applying conditioners such as elemental sulphur, aluminium sulphate and iron sulphate. However if your soil is thin and overlies chalk, then it will ultimately revert back to an alkaline state as the ground water seeps in. Tell-tale signs of high pH damage are yellowing leaves that turn brown. Azaleas grown in alkaline soils will eventually die as the plant becomes starved of essential nutrients.

Taking Care of Azalea

Water thoroughly during dry weather, especially container grown plants. Mulch with ericaceous organic matter in spring and apply a general fertilizer suitable for azaleas.

Dead head after flowering to prevent self-seeding.

Pruning Azalea

Pruning is not normally necessary, except to maintain shape or restrict excessive growth. Old, straggly, hybrids may benefit from regeneration pruning when dormant in winter, which should induce compact new growth in the spring. However, excessive hard pruning can easily kill azaleas. If you really need to prune back hard, then cut back one or two branches first to see if new growth emerges in the spring.

Cut out any dead or damaged wood and remove suckers from grafted plants.

Pests and Diseases

Susceptible to attack by rhododendron bug, vine weevil, leafhopper, lace bug, scale insects, caterpillars and aphids.

Vine weevils are particularly prevalent in container grown plants. If you see any of the adult weevils or find the white grubs in the soil, apply a biological control for vine weevils. Otherwise they will easily spread throughout the garden damaging other plants.

Can be affected by powdery mildews, petal blight, bud blast, silver leaf and honey fungus.

Propagating Azalea

Sow seed in warm frame or greenhouse from February to April. Cultivars will not come true from seed and often hybridise with any nearby azaleas.

Take 3in (7.5cm) cuttings of side shoots of evergreens in September-October. Take 3in (7.5cm) cuttings of young growth of deciduous azaleas in spring under mist. Alternatively layer low level branches in autumn.

Popular Varieties of Azalea Grown in the UK

Hybrid forms are best for the garden, as they are usually tougher and more tolerant of UK weather conditions.

Deciduous Azaleas

Deciduous forms provide spectacular colour in late spring and early summer. Many also have attractive autumn foliage. Three main deciduous cultivar groups include:

  • Ghent azaleas. these have small scented flowers. Height and spread to 8ft (2.5m).
  • Knap Hill and Exbury azaleas. These have larger, colourful trumpet-shaped flowers in May. Height to 8ft (2.5m), spread to 10ft (3m).
  • Mollis azaleas. These have large, unscented flowers that appear before the leaves in early May. Height to 6ft (2m), spread to 8ft (2.5m).

Some good varieties include:

Rhododendron 'Cecile' (Knap Hill) has large, pink flowers with a yellow flare.

Rhododendron 'Christopher Wren' (Mollis). Compact form with bronze leaves in autumn. Deep yellow flowers with an orange flare.

Rhododendron 'Coccinea Speciosa' (Ghent). Spreading form with bright scarlet-orange flowers.

Rhododendron 'Daviesii' (Ghent). Late flowering with creamy white, flared yellow, fragrant blooms.

Rhododendron 'Gibraltar' (Knap Hill). Red buds open to orange-red flowers with frilled margins.

Rhododendron 'Homebush' (Knap Hill). Pink, semi-double in dense, rounded trusses.

Rhododendron 'Klondyke' (Knap Hill). Young foliage is bronze-red. Flowers deep golden-yellow, flushed red.

Rhododendron 'Koster's Brilliant Red' (Mollis). Bright orange-red flowers.

Rhododendron 'Strawberry Ice' (Knap Hill) has pale pink flowers with a yellow flare.

Evergreen Azaleas

Evergreen forms are more compact than deciduous types, creating low growing mounds that are densely packed with blooms. Three main evergreen cultivar groups include:

  • Kaempferi azaleas. These are often semi-evergreen, with largish single flowers in mid- to late May. Height to 4ft (1.2m), spread to 5ft (1.5m).
  • Kurume azaleas. These have smallish single or double flowers in April-May. Height to 4ft (1.2m), spread to 6ft (1.8m).
  • Vuyk (Vuykiana) azaleas. These produce larger flowers in May. Height to 3ft (1m), spread to 5ft (1.5m).

Some good varieties include:

Rhododendron 'Addy Wery' (Kurume) is a compact form with orange-red flowers.

Rhododendron 'Blaauw's Pink' (Kurume) has rich salmon-pink blooms.

Rhododendron 'Blue Danube' (Vuyk) has large deep violet-blue flowers.

Rhododendron 'Hinode Giri' (Kurume) is a free-flowering, form with bright red flowers.

Rhododendron 'Hinomayo' (Kurume) is a vigorous, free-flowering, form with bright pink blooms.

Rhododendron 'John Cairns' (Kaempferi) has orange-scarlet flowers. The leaves go bronze in winter.

Rhododendron 'Kure-no-yuki' (Kurume) is a dwarf form with white flowers that have a slight green flare.

Rhododendron 'Orange Beauty' (Vuyk) has salmon-pink flowers that are slightly frilled (early May).

Rhododendron 'Palestrina' (Vuyk) is an upright bush with white flowers flushed with green.

Rhododendron 'Rosebud' (Vuyk) is a spreading form with double, bright pink flowers. One of the best pink rose-form full double forms.

Rhododendron 'Vuyk's Rosy Red' (Vuyk) has large, deep rose-pink flowers with slightly frilled lobes.