Rhododendrons are popular woodland shrubs that produce magnificent flowering displays during spring through to early summer. Their height and spread is variable depending on the chosen variety, but most are medium or large evergreen shrubs. (Azaleas are usually smaller and can be evergreen or deciduous.)
Originating mainly from the Himalayas, rhododendrons were introduced to the UK during the late 18th century. Over the past hundred years plant breeders have developed many exotic hybrids with approximately 20,000 registered varieties. The Rhododendron Society was established in 1915 and their first AGM was held at Chelsea in 1916. It became the Rhododendron Association in 1927 and then the Rhododendron Group after being absorbed into the RHS in 1945.
Our display benches look stunning at this time of the year with so many rhododendron varieties to choose from meaning that you can take away instant colour for your garden that will continue flowering year after year.
There's lots of varieties to choose from in the most gorgeous colour combinations. Here are three of our favourites:
A vigorous, compact, dense, evergreen shrub that produces rounded clusters of funnel-shaped red blotched, deep pink flowers in late spring/early summer: 4.9ft x 4.9ft (150cm x 150cm.)
(Top left image.)
Rhododendron Golden Torch:
The late spring pale yellow flowers of Golden Torch make this a particularly eye-catching rhododendron. RHS Award Of Garden Merit. Height & spread in ten years: 1.5m x 1.5m (4ft 11in x 4ft 11in.)
(Top right image.)
The flower clusters of this beautiful evergreen, glossy leaved rhododendron are pale pink with darker edges. Height & spread in ten years: 36in x 4ft 4in (90cm x 130cm).
Rhododendrons require acid soil with a pH between 5.0 and 6.0 that is moist but well-drained and rich in organic matter. Soil pH can be measured using a testing kit. If your soil is alkaline rhododendrons and other acid loving plants can be grown in containers using ericaceous compost.
Planting in the ground:
The chosen site should sheltered from cold, drying winds and be in dappled shade. Avoid planting rhododendrons in deep shade, frost pockets and sites that are exposed to early morning sun.
Before planting your rhododendron dig in plenty of neutral or acidic organic matter such as leaf mould, composted tree bark or spruce needles. Plant the rhododendron so that the roots are just covered - do not cover too deeply as they are surface-rooting.
Apply a mulch of chipped conifer bark or other acidic material to a depth of at least 7.5cm (3in). Do not firm the mulch down as it needs to be well-aerated. Mulch again each spring.
Water well until established using rainwater.
Planting in containers:
The RHS recommends using John Innes ericaceous loam-based potting compost when planting rhododendrons in containers. Their research has shown that soil-less potting medias including ericaceous peat-free potting composts are suitable for rhododendrons but over time they can lose their structure which leads to poor drainage and an airless environment for roots. This can lead to leaves going brown and dying back.
Rhododendrons should be re-potted every other year into fresh potting compost in early spring when signs of near growth appear. If you want to put your rhododendron back in the same pot carefully trim off up to one third of the roots which will make room for the fresh compost. Replace the top 5cm (2in) of compost in each intervening year.
Rainwater should be used for watering rhododendrons as tap water contains too much calcium which reduces acidity around their roots. If rainwater runs out tap water can be used for a month or two during the summer if necessary.
Apply a general fertiliser such as Fish, Blood and Bone or Vitax Q4 in late winter or early spring. If the rhododendron is in a container feed with a liquid fertiliser in the summer or add slow release fertiliser pellets to the compost.