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Shrubs

Rhododendron calendulaceum (A)

flame azalea

A deciduous azalea, usually to about 2.5m high in cultivation, though occasionally to 5m in its native habitat. An upright, loosely branching habit and elliptic, dark green leaves that turn orange and red in autumn. Young shoots are covered with fine bristly hairs. Produces clusters funnel-shaped flowers, in vivid shades of yellow, orange and red, in late spring and early summer

Synonyms

Azalea calendulacea

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Ultimate height

1.5–2.5 metres

Time to ultimate height

5–10 years

Ultimate spread

1.5–2.5 metres

Clay

Loam

Sand

Moisture

Moist but well–drained

pH

Acid

	Stem	Flower	Foliage	Fruit
Spring
Summer
Autumn
Winter

Partial shade

Aspect

West–facing

Exposure

Sheltered

Hardiness
Hardiness ratings
All ratings refer to the UK growing conditions unless otherwise stated. Minimum temperature ranges (in degrees C) are shown in brackets
H1a: under glass all year (>15C)
H1b: can be grown outside in the summer (10 - 15)
H1c: can be grown outside in the summer (5 - 10)
H2: tolerant of low temperatures, but not surviving being frozen (1 to 5)
H3: hardy in coastal and relatively mild parts of the UK (-5 to 1)
H4: hardy through most of the UK (-10 to -5)
H5: hardy in most places throughout the UK even in severe winters (-15 to -10)
H6: hardy in all of UK and northern Europe (-20 to -15)
H7: hardy in the severest European continental climates (< -20)

Botanical details

Family: Ericaceae
Native to the UK: No
Foliage: Deciduous
Habit: Columnar upright, Spreading branched
Potentially harmful: Harmful if eaten. Wear gloves and other protective equipment when handling. Pets (dogs, cats, rabbits, tortoises) Harmful if eaten - for further information and contact numbers regarding pets, see the HTA guide to potentially harmful plants
Genus: Rhododendron can be evergreen or deciduous shrubs or trees, with simple leaves, sometimes with a dense colourful indumentum of hairs on the lower side, and funnel-shaped, bell-shaped or tubular flowers that may be solitary or in short racemes
Name status: Correct
Horticultural Group: Azaleas can be deciduous or evergreen, with mostly small, frequently fragrant, funnel-shaped flowers in spring or early summer; deciduous azaleas often have good autumn colour

How to grow

Cultivation

Grow in moist but well-drained, humus rich, acidic soil, in part-day shade; some hours of sun are required to develop the best colours. Choose a site away from frost pockets and sheltered from strong winds, and do not allow plants to dry out. Mulch annually, ideally with leaf mould. See rhododendron cultivation for more detailed advice

Propagation

Propagate by semi-ripe cuttings in late summer, or by grafting in winter

Suggested planting locations and garden types

City and courtyard gardens
Cottage and informal garden
Flower borders and beds
Wall side borders

Pruning

Minimal pruning required, may be lightly pruned after flowering; see pruning group 1

Pests

May be susceptible to vine weevil, rhododendron and azalea whitefly, rhododendron leafhopper, Pieris lacebug, scale insects, caterpillars and aphids

Diseases

May be susceptible to powdery mildews, honey fungus, silver leaf and Phytophthora, as well as more specific Rhododendron diseases

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