We have rhododendron (Rhododendron ponticum) in many of our woodlands, on our reservoir and lake edges and even on our moorland sites. Rhododendron is a beautiful plant and can transform a site into a picturesque paradise when it is in full bloom, but if left unchecked, this non-native species can become very invasive and lead to a significant loss in biodiversity.

Rhododendron is not native to the UK, it is an invasive non-native species. It was introduced here in the 1700’s as an ornamental plant and is native to the Mediterranean.  

We are working in partnership with South West Water to help protect our sites from the impacts of invasive non-native species. 

Rhododendron is the most damaging and most widespread terrestrial invasive non-native species in Britain (Parrot and MacKenzie, 2013). Rhododendron is listed on the Wildlife and Countryside Act (1981) under Schedule 9. This piece of legislation makes it an offence to release or allow it to escape into the wild. Therefore, we are taking action to control it.  

Not only is rhododendron listed on legislation, it also has other negative impacts to our sites;

  • It is a very successful plant which out competes many of our native plants by forming thick, shady thickets, preventing most flora from growing underneath it
  • It impacts our lakes and reservoirs by altering algal growth, litter and invertebrate abundance and assemblage – more information here 
  • It is poisonous to livestock, pets and wild animals
  • It is a host plant for diseases which attack oak and beech trees (such as Phytophthora ramorum and Phytophthora kernoviae)
  • It does not support other biodiversity as well as our native tree and shrub species e.g nesting birds and bat roosts  
  • Pollinators such as bees, flies and butterflies spend time pollinating rhododendron rather than our native plants
  • Honey made from bees foraging on rhododendron can cause grayanotoxin poisoning symptoms being light-headedness and hallucinations, loss of consciousness and muscle weakness (Jansen et al., 2012)
  • Chemicals in the leaves make it unpalatable to vertebrates
  • Controlling rhododendron is very costly and time consuming if left to colonise large areas. 

There is more information about rhododendron here.

To manage and control rhododendron effectively, it needs to be cut to the base and have all of the roots dug out and/or be treated with herbicides. The management of rhododendron is a long term process as the seeds can remain alive in the soil for many years after the main plant is dead so constant vigilance for new plants is required.

This winter (2023-2024) we are removing rhododendron from several of our County Wildlife Sites. These are Lower Tamar Lake, Wimbleball Lake, Porth Reservoir and Drift Reservoir. The rhododendron at these sites is in our woodlands and on the reservoir edges. In order to improve the quality of the habitat (known as its ecological condition) the rhododendron needs to be removed. We are hiring contractors to do this work for us. After the removal, the area will look different but it will soon bounce back as we will allow the local seed bank to flourish with native grasses, flowers, shrubs and trees.  

Healthy broadleaved woodlands are an important habitat for animals such as birds, butterflies, moths, amphibians and bats. Not to forget the plants, bryophytes and fungi which benefit too. There is more information on broadleaved woodlands here.

To be a healthy woodland, they must not be overrun by invasive non-native species. We will be improving this habitat for now and the future.

Our County Wildlife Project has identified important habitats that we want to protect. Now, we are doing habitat management to improve these sites. Rhododendron isn’t the only invasive non-native plant that we managing, we also have Himalayan balsam, Japanese knotweed, American skunk cabbage, New Zealand pygmyweed and cherry laurel.




J. Parrot and N. MacKenzie (2013) A critical review of work undertaken to control invasive rhododendron in Scotland; A report commissioned by Forestry Commission Scotland and Scottish Natural Heritage. Collie Alba.  

S. A., Jansen, I. Kleerekooper, Z. L., M., Hofman, I. F., P., Kappen, A. Stary-Weinzinger and M. A., G. van der Heyden (2012) Grayanotoxin Poisoning: ‘Mad Honey Disease’ and Beyond.  Cardiovascular Toxicology. 12:2018-215.