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Rhododendron

Rhododendron (including azaleas) · Ericaceae

Showy spring flowers

Photo: JoachimKohler-HB, CC BY-SA 4.0, via Wikimedia Commons

Sun: Dappled or part shade, sheltered; some tolerate full sun; dwarf alpines tolerate sun
Soil: Moist, well-drained, acid
Soil pH: Acid, ideally pH 5.0-6.0; some tolerate neutral soil
Water: Water with rainwater in dry spells; hard tap water raises pH
Hardiness: Mostly fully hardy; some cultivars need shelter from cold winds
Height and spread: Variable: from dwarf alpines to large shrubs over 2m

Guv's tipWater rhododendrons with rainwater in dry spells; hard tap water raises the pH. They want moist, acid soil. Trust me on this one.

Through the year

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Sow or plant

In flower

Timings are for the UK as a whole. Northern and exposed gardens often run a couple of weeks later.

When to plant

Autumn or spring (Mar-Apr, Sep-Dec)

Flowering

Mainly spring into early summer (Apr-Jul)

Pruning

Deadhead after flowering; little pruning needed beyond removing dead or damaged wood

Making more plants

Layering, cuttings (cultivars); seed for species

Watch out for

Pest

Vine weevil

Look for: Notched leaf edges (adults); C-shaped grubs eat roots, plants wilt and collapse

What to do: Nematode drench (Steinernema kraussei) in late summer/autumn, pick off adults at night

Pest

Scale insects

Look for: Flat brown scales on stems and leaves, honeydew

What to do: Wipe off, encourage natural enemies

Disease

Honey fungus

Armillaria spp.

Look for: White fungal sheets under bark at base, dieback, bootlace rhizomorphs

What to do: No chemical control. Dig out and destroy affected plants including roots; physical root barriers

Always read and follow the label on any treatment, and check it is approved for use where you live.

Safety and spread

Pets and people: Toxic to people and pets (grayanotoxins), causing vomiting, diarrhoea and heart effects

Weed risk: Rhododendron ponticum, R. luteum and R. ponticum × maximum are listed invasive plants: it is illegal to plant them or cause them to grow in the wild. R. ponticum is invasive in UK woodland

Checked against two or more reputable gardening sources. How we check our facts

Growing somewhere else? See this plant for the USA.

Keep it by the back door

The Plant Doctor and the Guv's book

Printable pest and disease charts with real photographs, and all 50 UK plants in one book.

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