Rhododendron Ponticum

What is Rhododendron Ponticum?

Rhododendron Ponticum is a large evergreen shrub and an Invasive Non-Native Species (INNS) found widely throughout Scotland. There are several different varieties of Rhododendron cultivars across the country, which have been produced through selective breeding, however it is this vigorous hybrid of the plant has become a significant issue.

Like many troublesome non-native species, Rhododendron Ponticum was first introduced to the UK as an ornamental plant during the Victorian period. In its native environment of Eastern Europe and Western Asia, Rhododendron is neither vigorous or invasive. It was the selective breeding with frost-hardy variants of Rhododendron species from North America that gave rise to the highly fertile Ponticum hybrid, which is now considered to be one of the biggest challenges that we have with invasive plants in Scotland today.
Despite its invasive nature, it is a beautiful ornamental plant that produces vibrant purple flowers between May & June.

Why is it a problem? Rhododendron Ponticum is extremely resilient to the harsh Scottish climate and has a high tolerance to shaded, low light conditions. This, combined with its high fertility, has enabled it to out compete our native flora and thrive throughout the country. It forms large, dense closed canopies that block out the light for anything else to grow within our woodlands and open land. It is an aggressive coloniser and huge threat to biodiversity, with its management a top priority for a number of key organisations in Scotland, such as National Trust Scotland and the Forestry Commission.

How does it spread? A mature plant, growing in ideal conditions can produce up to one million seeds per year, which remain viable for 12 months. Even smaller plants are able to produce several thousand seeds each year. Rhododendron Ponticum seeds ripen during December and January and dispersal takes place across February and March. Growth is initially very slow, however this increases significantly over time. As the plant grows, branches are able to graft and take on new roots through stem layering and brach collapse, further enabling spread over longer periods of time, where soil conditions are not conducive to invasion by seedlings. 

Rhododendron Legislation?

 Rhododendron Ponticum is covered by the Wildlife and Countryside Act 1981. It is listed under Schedule 9 of the Act, which cites that it is an offence to plant or otherwise cause the species to grow in the wild. In Scotland, it is controlled under the Wildlife and Natural Environment Act 2011, which states that it is an offence to release or cause the release of any plant to a place outside of its native range.

Rhododendron Ponticum
Rhododendron Ponticum

Rhododendron Ponticum Treatment

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Stem Treatment 

Minimal doses of herbicide is carefully applied into drilled reservoirs on the plant’s branches and stems, with minimum disturbance to other plants and wildlife within the area.

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Stump Treatment

It’s particularly useful for previously cut plants with multiple stems. After cutting plants down to near ground level, stumps are drilled on all sides and solution injected into the reservoirs.

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Foliar Application

Herbicide application over the entire leaf area works best on very dense, low growing multi-stemmed plants, and it covers large areas quickly. Typically applied by knapsack sprayers using operatives who are trained and competent in the safe use of herbicide.

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Combined Treatment

As with all Invasive Non-Native species, the method for treatment is dependent on a number of factors that are assessed during survey and often results in an integrated approach using a combination of treatment methods over an extended period of time.

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