A large family of mainly evergreen, hardy spring flowering shrubs. Mainly shade loving, rhododendrons are one of the most spectacular of all the early flowering shrubs available in the UK. They are available in a range of striking colours, from purple, red and pink to pure white.
Family: Ericaceae (Heath Family)
Botanical Name: Rhododendron
Foliage: Evergreen simple glossy leaves.
Flowers: Funnel-shaped, bell-shaped or tubular flowers, usually in short racemes. In shades of purple, red, pink and white.
Flowering Period: Most forms flower from May to June.
Soil: Moist but well-drained soil (clay, sand or loam). Acid pH.
Conditions: Full sun or partial shade. Any aspect in a sheltered location.
Type: Shrub or small tree.
Hardiness: Hardy in most regions of the UK.
Thrives in moist but well-drained, humus-rich, acid soil. Not suitable for chalky soils. Mix plenty of well-rotted leaf-mould with the planting medium. Do not plant bushy species too close together but allow them room to grow and spread naturally.
Most forms are shade tolerant but will require some sun for part of the day to flower well. Ideal for a partly-shaded or woodland garden.
Nearly all rhododendrons need acid soil. To grow them successfully you will need a soil pH value below 7. If you are unsure of your soil pH level then use a pH soil testing kit, available from most garden centres. If you live in an alkaline or chalky area, your best option is to grow compact varieties of rhododendrons in containers filled with ericaceous compost. However, there are a few species that are reasonably tolerant of alkaline conditions. These include:
Water thoroughly during dry weather until well established. Mulch with ericaceous organic matter in spring and apply a general fertilizer suitable for Rhododendrons.
Rhododendrons keep their roots near the surface, so take particular care when weeding of digging around them. Because they are shallow, surface-rooters, they can be easily transplanted so long as the root ball is kept intact.
Dead head after flowering to prevent self-seeding and help keep the plant tidy. Regularly bush away any fallen petals from the leaves as they can easily mar the evergreen foliage if left to rot on the plant.
Little or no pruning is necessary, apart for the removal of dead, diseased or damaged wood. Do not prune young bushes, until they are well established. Rhododendrons don't respond well to hard regenerative pruning as this may damage and shorten the life of the plant. Therefore it is best to plant them with sufficient space, so they can grow and reach their full potential, without the need to cut them back.
Susceptible to 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 can easily spread throughout the garden damaging other plants.
Can be affected by powdery mildews, petal blight, bud blast, silver leaf and honey fungus.
Seed can be sown outdoors in spring, although cultivars will not come true to type.
Semi-ripe cuttings can be taken in late summer. Alternatively, layer low branches in autumn.
As the result of several hundred years of hybridisation, these magnificent shrubs are now available in a vast array of colours and sizes. Most varieties flower around May-June but a few will also bloom from Christmas onwards.
Rhododendron 'Bluebird'. A dwarf, small leaved shrub, with clusters of saucer-shaped violet-blue flowers in April. Height and spread to 3ft (90cm.
Rhododendron 'Blue Peter'. Strong-growing, upright habit. Pale violet blue flowers in May. Height to 10ft (3m), spread to 16ft (5m).
Rhododendron 'Britannia'. Slow-growing, compact, rounded bush. Red blooms in May-June. Height to 6ft (1.8m), spread to 8ft (2.5m).
Rhododendron 'Cunningham's White'. Compact form with pale mauve flowers in May, later turning to pure white, spotted with yellow and purple. Height to 10ft (3m), spread to 13ft (4m).
Rhododendron 'Cynthia'. Vigorous form with deep rose-pink, flowers in May. Height to 20ft (6m), spread to 23ft (7m).
Rhododendron 'Dora Amateis'. A compact form with pink-tinged white flowers with green markings. Height and spread to 3ft (90cm).
Rhododendron 'Elizabeth'. Makes a compact, spreading bush, with funnel-shaped deep scarlet flowers in April. Height to 3.5ft (1.2m), spread to 10ft (3m).
Rhododendron 'Fabia'. A spreading form with lax trusses of bell shaped orange flowers, in late May-June. Height to 5ft (1.5m), spread to 10 ft (3m).
Rhododendron 'Fastuosum Flore Pleno'. Tall, domed, bushy form with mauve flowers in late May-June. Height to 10ft (3m), spread to 16ft (5m).
Rhododendron 'Gomer Waterer'. Compact bush with mauve in buds opening white, with mauve-pink edges, in early June. Height to 10ft (3m), spread to 15ft (4.5m).
Rhododendron 'Hummingbird'. A compact, rounded shrub, with glossy green foliage. Lax trusses of bell-shaped, deep glossy scarlet flowers from April to early May. Height and spread to 6ft (1.8m).
Rhododendron impeditum. A dense, low growing, spreading shrub with tiny, aromatic leaves. Pale purplish-blue flowers cover the plant from April to early May. Height 1ft (30cm), spread to 1.5ft (45cm).
Rhododendron 'Mrs A. T. de la Mare'. A compact bush with white flowers with a green flare, in June. Height to 6ft (2m), spread to 10ft (3m).
Rhododendron 'Mrs G. W. Leak'. A vigorous, compact bush with pale pink flowers, heavily dotted with reddish-purple, in May. Height and spread to 15ft (4.5m).
Rhododendron pemakoense. A dense, dwarf shrub, with dark green leaves. Relatively large, funnel-shaped, purplish-pink flowers in late March-April. Height to 1.5ft (45cm), spread to 2ft (60cm).
Rhododendron 'Pink Pearl'. Forms a large bush with pale pink flowers, in May-June. Height and spread to 16ft (5m).
Rhododendron 'Praecox'. A small semi-evergreen shrub with clusters of funnel-shaped, rose-purple flowers in February-March. Can be damaged by late frosts. Height and spread to 5ft (1.5m).
Rhododendron ponticum (common rhododendron). A vigorous shrub or small tree, with funnel-shaped, mauve or purple flowers, in rounded trusses in June. The variety 'Variegatum' has creamy white leaf margins. Height and spread to 20ft (6m) or more. Can be found naturalised around many areas in Britain with acid soils.
Rhododendron 'Purple Splendour'.
A vigorous, upright shrub, with imperial purple flowers,
in May-June. Height to 8ft (2.5m), spread to 12ft (3.5m).
Rhododendron 'Sappho'. A large, dome-shaped bush with white flowers blotched with blackish purple, in late May to June. Height to 15ft (4.5m), spread to 20ft (6m).
Rhododendron 'Scarlet Wonder'. A compact low growing shrub with glossy green, deeply veined, leaves. Bright scarlet bell shaped flowers in May. Height to 2ft (60cm), spread to 3ft (90cm).
Rhododendron williamsianum. A small bush with small, rounded leaves. Loose clusters of broadly bell shaped, pale pink, flowers in April. Height and spread to 5ft (1.5m).