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Garden Features
Rhododendron Dell
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Rhododendrons are one of the largest and most spectacular groups of flowering shrubs, showing great variation in size, habit and form. Over 700 specimens of hardy species and hybrids are planted within the Rhododendron Dell, some of which are unique hybrids found only at Kew.
Growing conditions are favourable for Rhododendrons within the Dell as the River Thames runs parallel to the area, increasing humidity. Shade is provided by many trees including the Oak trees, which form part of the Quercus collection. The soil, which is not naturally acid, is treated with high-acidity organic mulch and sulphur treatments to reduce the pH level of the soil to one that is more appropriate for Rhododendrons.
While it may look a natural valley today, Capability Brown carved the area out of the River Thames floodplain in 1773, when he created what was then called Hollow Walk. It only became the Rhododendron Dell when Sir Joseph Hooker began bringing back Rhododendrons from his Himalayan expeditions in the 1850s. From then the collection grew rapidly, until the early 1970s when much of it was moved to Wakehurst Place where there was additional room and where growing conditions seemed as favourable.
Many specimens remained and thrived in the conditions, but in more recent times several factors have affected the collection. These include the loss of shade-providing Elms in the late 1970s, due to Dutch Elm Disease, the storms of 1987 and 1990, attack by Armallaria fungus, and prolonged periods of drought. We are reacting to these factors by planting new trees, which is creating more shade; treating the area with high-acidity mulch; and by adding soil conditioners which is helps the remaining Rhododendrons to thrive.
The original planting is being augmented with the planting of more Rhododendron hybrids and species as well as other plants to extend the period of interest. This has helped to recreate much of the splendour of the original Rhododendron Dell, making it one of the most popular areas to visit.
There are several notable specimens of Rhododendron within the collection. The oldest at Kew is Rhododendron campanulatum though several plantings that can be seen today are from the original planting. Many of the Rhododendrons are highly scented, including Rhododendron kewense "King George" and Rhododendron loderi. The largest planting, however, is of Rhododendron "Cunningham's White", which is particularly suited to the conditions at Kew and provides a brilliant mass of white flowers each spring.
Whilst the flowering period can extend from November to August, with contrast and diversity of leaf and flower shape, size and colour, the best time to visit is during late May when the majority of Rhododendrons will be in flower.
Interest within the area is extended throughout the year with plantings of other trees (including Fagus, Castanea, Acer, Betula and Ilex), shrubs (including Magnolia, Peris and Camellia), and herbaceous perennials (including Hosta, Pulmonaria, Hemerocallis, Ferns, Iris and Hellebores).
A collection of Azalea Rhododendrons can be found in the Azalea Garden, and less hardy and frost tender Rhododendrons and Azaleas can be found in the Temperate House.
The Rhododendron Dell is number 34 on the Visitor Map.