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
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.
Type: Small shrub.
Hardiness: Hardy in most regions of the UK. Protect early flowering forms from late frosts.
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.
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.
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 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.
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.
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.
Hybrid forms are best for the garden, as they are usually tougher and more tolerant of UK weather conditions.
Deciduous forms provide spectacular colour in late spring and early summer. Many also have attractive autumn foliage. Three main deciduous cultivar groups include:
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 forms are more compact than deciduous types, creating low growing mounds that are densely packed with blooms. Three main evergreen cultivar groups include:
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.