Rhododendron ponticum is an evergreen, ornamental plant that was first introduced to the UK, via Gibraltar in 1763 by the nurseryman Conrad Lodiges (Cronk and Fuller, 1995).
By 1803, R. ponticum was being sold on London markets as a flowering pot-plant and was established throughout England as an ornamental in stately homes and in estates, where it provided cover for game animals. For many years, R. ponticum was more or less restricted to these artificial habitats but with the gradual erosion of large estates and the attendant workforces, the plant was allowed to spread unchecked. Molecular studies support Iberia as the origin of UK material.
The invasiveness of the species was being documented in Wales from 1943.
R.ponticum wide native distribution covering an area south of the Black Sea, including Bulgaria, Turkey (Bean, 1976), Georgia (USDA-ARS, 2003), the Krasnodar region of southern Russia (Czekalski, 1998; USDA-ARS, 2003) and Lebanon (Cross, 1975), and may be or may have been also native to Syria. Small pockets of native habitat are found in south western Spain and central and southern Portugal where R. ponticum subsp. baeticum is found.
Classified as an invasive non-native species, rhododendron ponticum is responsible for the destruction of many native habitats. On acid soils including moorland, woodlands, screes, rocky banks, derelict gardens and streamsides (pre-dominantly in the West), it will out-compete most native plants, as it can grow to many times the height of a person, and in doing so, allows very little light to penetrate through its thick leaf canopy.
As well as eliminating other native plant species, it results in the loss of associated native animals. It can also have wider implications for tree health as it is a host for phytophthora.
Rhododendron ponticum has evergreen, lanceolate leaves up to 7.5 inches long, with smooth margins. They are dark green with a glossy upper surface and a dull underside. Large trusses of bell-shaped violet to purple coloured flowers bloom from spring to early summer.
How does it spread?
Rhododendron ponticum spreads vegetatively and by seed. Established plants can spread by lateral horizontal growth of the branches, and where these touch the ground, they will root, continually extending the area of cover. Over time, a single plant may cover many metres of ground with thickly, interlaced, impenetrable branches. This strategy allows the plant to extend into areas which would otherwise be unsuitable, eg areas of wetland can be dominated by the canopy, whilst the main stem and roots are on suitable dry land.
Dispersal
Rhododendron seeds are very small and are dispersed by the wind. Each flower head has the potential to produce between 3000-7000 seeds, so a large bush can produce several million seeds per year. Given the high numbers of seeds produced, it only needs a small proportion to germinate successfully. Established seedlings succeed best in disturbed areas.
Control strategies
If established stands are not kept in check, they will expand into adjacent areas, eliminating rapidly the majority of native plant species. For removal, all above ground growth must be cut, sawed or pruned. Where possible, the woody material can be chipped and used as mulch, and the green material rotted down into compost for use at a later date.
The stumps can be removed or treated with an injection of herbicide. If the latter option is preferred, a follow-up management plan over a three to five year period is required for any subsequent regrowth of plant material. If rhododendron ponticum or rhododendron maximum is present in your garden or on your land, please consider the wider health of woodlands in your area.
