Rhododendrons produce spectacular, sometimes, strongly scented flowers, which are borne from singly or in lateral or terminal racemes (trusses) from late autumn to late summer. The individual flowers vary greatly in size and shape and are often marked with flares or spots inside.
There are thousands of hybrids, encompassing nearly every flower colour. Some have attractive young growth, a few have decorative, exfoliating bark and a number are valued for their autumn colour.
Rhododendrons have a wide range of garden uses; dwarf alpine varieties are effective in a rock garden; larger woodland rhododendrons are excellent for brightening shady areas; the hardy hybrid rhododendrons are tolerant of more exposed sites and also suitable for hedges or informal screens; and many of the modern compact hybrids are ideal for growing on shaded patios, or in containers or tubs.
Rhododendrons are split into various groups the most popular are:-
These have green leaves all year round and include the “hardy hybrids”. They vary in habit from small, cushion-forming shrubs to tree rhododendrons. They have small to large leaves and flowers in a variety of shapes, sizes and colours.
Evergreen and deciduous azaleas
Are small to medium-leaved shrubs belonging to the genus Rhododendron, and commonly known to gardeners as azaleas. They bear a profusion of small to large trusses of usually small flowers in a variety of shapes.
Outdoors, grow rhododendrons in moist but well-drained, leafy humus-rich, acid soil (ideally Ph4.5 – 5.5). Shallow planting is essential: all rhododendrons are surface rooting and will not tolerate deep planting. Most large-leaved species and hybrids require dappled shade in sheltered woodland conditions: avoid deep shade immediately beneath a tree canopy.
Most of the other groups, including the “hardy hybrids”, thrive in light dappled shade or part-day shade, but not early morning sun; they will tolerate a more open site if given shelter from cold, dry winds. Avoid frost pockets to reduce the risk of water logging and bark split.
Feed with ericaceous slow release fertiliser and mulch annually with leaf mould in spring. After flowering, deadhead where practical to promote vegetative growth rather than seed production. Carefully pinch out the spent flower heads before the new shoots emerge. After flowering, lightly trim or prune back shoots that spoil symmetry.
If planting in containers or tubs add clinker to the bottom of the pots for drainage, put in a layer of ericaceous compost; add ericaceous mycorrhizal fungi ensuring the roots of the plant are in contact to encourage secondary roots: then back fill around plant with more ericaceous compost mixed with ericaceous slow release fertiliser. Firm the plant in, place in position and water well.
Rhododendron ‘Cunningham’s White’ is a robust hardy hybrid, with dark green evergreen foliage and loose trusses of funnel-shaped white flowers opening from mauve buds in late spring. Height and spread 1.5-2.5m (5’-8’) x 2.5-4m (8’-13’).
Rhododendron ‘Cosmopolitan’ produces pink flowers with dark red throats in May. It is a compact, evergreen shrub that grows to 1.5m (5’) in height and spread, perfect in garden borders and tubs.
Rhododendron ‘Goldbuckett’ is a vigorous evergreen shrub with trusses of funnel shaped, soft creamy flowers with red markings. Max Height 1.4m (4’-5’), spread 1.4m (4’-5’). Flowers May to June, best planted in sun or partial shade.
Rhododendron ‘Bengal’ produces hot red flowers in May. It is a compact and bushy evergreen plant that grows to 1m (3’) height and spread, perfect for small gardens, rockeries and tubs.
Azalea luteum is a deciduous shrub with mid-green leaves. It has pretty funnel-shaped, strongly scented, sticky yellow flowers in late spring to early summer. It will grow to a maximum height and spread of 4m (12’) and flower May-June in full sun.