Rhododendron calendulaceum (A)

Synonyms

Azalea calendulacea

Shrubs

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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

Position

Partial shade

Soil Types

Clay, Loam, Sand

Max Height

1.5-2.5 metres

Max Spread

1.5-2.5 metres

Size

Time to Maturity: 5–10 years
Max Spread: 1.5-2.5 metres
Max Height: 1.5-2.5 metres

Growing Conditions

Clay Loam Sand

Moisture: Moist but well–drained
pH: Acid

Position

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): H6

Colour & Scent

Season	Stem	Flower	Foliage	Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family: Ericaceae
Native to GB/Ireland: 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

Horticultural Classification Codes

Horticultural Classification Codes are often given to genera which have a large number of species or cultivars. They are used to categorise cultivated plants based on specific, shared characteristics such as shape, colour, size or flowering time, and can be displayed as letters or numbers

For example:
Dahlia ‘Sunset Kate (Sin) = Single flower
Rosa ‘Marigold’ (HT) = Hybrid Tea: 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