Invasive species -2 Rhododenron ponticum

A look at the species that is causing conservation concern

Get to know the Rhododendron ponticum.

Rhododendron ponticum is a native species of Asia,Spain,Portugal and Bulgaria. It was introduced into the U.K. as an ornamental shrub originally grown at Kew Gardens. It is a tall gangly shrub, almost tree like in habit, if left to its own devises. It is thought that the majority of these shrubs in the U.K. have their origins in Spain.

as an ornamental plant grown in many large gardens it soon escaped over the wall to become established in the wider countryside, particularly in woodland. However, the habitat varies greatly and they may be encountered on acidic heath land, scrub land, peat land, sand dunes and along roadside verges.

Below--the species soon invades woodland

Photograph by Dal.

Basic Biology of Rhododendron ponticum.

It is classed as a shrub or small tree which produces suckers which aid in its spread. It may attain the height of 5 m rarely specimens of up to 8 m tall have been recorded. The foliage is evergreen and between 6-18 cm long {two and a half to seven and a quarter inches} and up to 5 cm wide.{two inches}

The flowers which are often numerous are of a violet blue colouring, trumpet shaped and tubular, they are succeeded by elongated dry capsules which contain a plethora of small seeds. The seeds and suckers allow quick expansion of the species.Flowers of the shrub are numerous and impressive.

Below--the flowers of R.ponticum bottom--the shrub is impressive when in flower Photographs by Dal

Conservation issues.

As far as many conservationists are concerned R.Ponticum is just another invasive species which is detrimental to native flora and wildlife in general. Studies have revealed it reduces biodiversity by forming dense stands which in turn produces dense areas of shade and deep leaf litter. This leaf litter imparts a toxic affect which is thought to last up to seven years  even when the perpetrator has been removed. As a woodland invader the shrub impacts on animals as well as native flora. Many of them rely on the native understory of hazel and hawthorn both of which are shaded out by this alien shrub. One example is the dormouse, but others include wood mouse, yellow necked mouse and bank voles.

Below  top the wood mouse courtesy of rasbak CC BY-SA 3.0 License.  Below -bottom a nest of bank voles courtesy of Plant surfer. CC BY-SA 3.0 License.

the foliage of R.ponticum is---

The foliage of R.ponticum is toxic to many herbivores because of a substance they contain called Diterpenes. A less known fact is that the honey produced from the flowers of this shrub is known to be toxic to humans Historical records allege that Greek soldiers were poisoned after consuming the honey whilst in Asia Minor.

many various ways have been employed in an attempt to eradicate this species from habitat where it is thought to be especially detrimental to native species. Digging them out with heavy machinery is not only expensive but in many cases impossible to achieve because of the type of habitat they tenant. Likewise cutting them down or trying to grub them out is also impracticable in many cases. Spraying with herbicide is indiscriminate and detrimental to other nearby flora.

However, the Forestry Commission faced with these difficulties have come up with a new scheme to eradicate the shrub. They have started to inject herbicide directly into the trunks and stems which results in the demise of the shrub within six months of being applied. This method is precise unlike the indiscriminate spraying. It also has the advantage that it is not washed off by the rain, which also prevents herbicides from entering the water system. Time will tell if the efforts are viable and successful. 

Below top-Rhododenron ponticum is completly frost hardy. Next to top-- spring flower buds. Next to bottom --leaf litter from this species is toxic  Bottom -the trunks of this species can mature into thick specimens.

photographs by Dal

Rhododendron and the garden

Whilst R.ponticum is not looked upon favourably in the wider countryside the cultivated relatives have won the affection in the hearts of many gardeners. To grow them successfully they need to be planted in acidic soil with ample drainage, thus grown in containers these requirements may be met fully.

Below--rhododendrons cultivated for gardens have wonderful flower colours

photograph by Dal

Some  garden favourites.

Rhododendron "Pink Pearl"--This species is an open , upright shrub which may attain the height of 12 M or more. It is evergreen and completely frost hardy. They produce bunches of funnel shaped flowers that are of a delightful pink colour providing stunning displays in late summer.

Rhododendron "President Roosevelt" This species has a handsome variegated foliage and bright red / pink flowers. It is named in honor of the 26th President of the United States Theodore Roosevelt.

Rhododendron "auriculatum" is an ever green shrub bushy and wide branching up to 20 feet. It is a completely frost hardy shrub that has large oblong leaves with ear like lobes at the base. it produces bunches of 7-15 large, heavily scented flowers, which are funnel shaped. It is another species that flowers in late summer. They grow best in light shade/light woodland.

Rhododendron "Queen of Hearts" -an evergreen, open shrub with a spread of 5-12 feet when mature. It is frost hardy. It produces domed branches with a plethora of funnel shaped deep crimson flowers which have dark flecks within. This species flowers in mid spring.

Rhododendrons play may play host to common garden pests such as aphids, leaf hoppers, lace bugs,scale insects and caterpillars. However, all these can be easily controlled and should not deter the gardener from growing these beautiful flowering shrubs.

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