Rhododendron Ponticum Identification

Read through our Rhododendron identification guide below. If you are still not sure, email us your photos and we'll confirm whether it's Rhododendron for FREE.

Quick Facts

  • Rhododendron outcompetes native flora
  • Rhododendron can cause ‘Mad Honey Disease’
  • Flowers in June and July
  • Shrubbery can create monocultures
  • Can produce over 1 million seeds a year

Trust us to give you the right information:

What does Rhododendron ponticum look like?

Rhododendron is a very large genus of woody plants that averagely reaches 3.5m tall and can be seen up to 10m tall in the wild. There are about 1,024 different species of Rhododendron which are usually native to North America, Asia or the Himalayas. Commonly known as Rhododendron or Azalea, these woody shrubs exhibit spectacular flower displays in the summer months in groups of 14 to 25 bell-shaped flowers that grow in clusters of pink or purple.

A common sight in many parts of the UK and in many ornamental gardens, Rhododendron ponticum has dark green, thick, glossy leaves that are evergreen. Woody stems become more like the trunk of a tree as Rhododendron ages.

Rhododendron can flower earlier or later dependent on its environment, for example it has been noted that in warmer climates flowering has been seen between December and March and in colder climates, between April and May.


The pink flowers of a rhododendron

How do you identify Rhododendron in the Winter?

Rhododendrons are evergreen and are winter hardy. In the winter, water evaporation occurs and the dark green leaves can droop and curl in slightly to protect themselves from the cold weather.

Rhododendron roots enter dormancy in the winter but can continue to grow if the soils thaw and become active again. This is called winter quiescence which is a tactic used by woody evergreen plants to absorb water from the soils to ensure they keep their leaves.

Rhododendron bud in winter

How does Rhododendron Grow?

Rhododendron can spread both by seed dispersal and something called Stem Layering.

Seeding

  • Seed spread occurs following flowering. Rhododendrons usually flower after around 12-20 years of growth, although this time can be reduced if the plant is recovering from cutting, flowers can be seen after about 2 years of regrowth. Mature plants can produce around 1 million seeds which can invade or re-invade an area with suitable ground conditions quite easily.
  • The most susceptible areas are disturbed ground and areas recently cleared of other mature vegetation.
  • Seeds only remain viable for around 1 year; however, germination can occur in many variations of soil conditions.
  • Seeds are very light and small, and dispersal is mostly windborne, reaching up to 500m from the parent plant.
  • Seedlings grow very slowly in the first few years, which can be a hindrance in control methods; monitoring visits need to occur for multiple years to ensure no further regrowth occurs.

Stem Layering

  • Slow vegetative spread that relies on fallen branches re-rooting in the ground.
  • Collapsed branches fall to the ground and can re-root in the ground. This is a slow process and is more often seen at the edge of stands of Rhododendron and where mature trees have fallen.
  • This spread causes densely interwoven stems in areas that otherwise may not be suitable for seed germination such as wet ground where seedlings would likely die.
Rhododendron bush with lilac flowers
Rhododendron bush with pink flowers

Interesting facts about Rhododendron ponticum

Introduced to the UK from Gibraltar in 1763 as an ornamental garden plant, by the mid-1800’s Rhododendron ponticum was being sold in London markets as a popular garden plant.

Rhododendron spreads via a powerful seed dispersal system and large infestations have been noted in the wild in upland areas around the country, particularly in the Snowdonia National Park in North Wales where a large-scale multimillion pound project has been undertaken to control the spread of the plant. Rhododendron was found to be growing at a rate of 1km every five years in the Hebrides in Scotland and cost approximately £120,000 per year to manage and eradicate!

Rhododendron roots are toxic! They produce grayanotoxins which are found in the leaves, roots and stems of the plant. This is used as a defence technique for the plant, ensuring grazing herbivores find the plant unpalatable. This is where ‘Mad Honey Disease’ comes from!

When bees pollinate the flowers of the plant and return the nectar to their hives, the honey that is produced contains the poisonous grayanotoxins and can cause significant stomach-upset and cardiac discomfort (Arrhythmia).

Rhododendron bush with pink flowers

Is Rhododendron a problem?

Yes!

As with other invasive species, Rhododendron ponticum is especially hardy and able to grow in many weather and soil conditions. This allows the plant to grow to large capacities around the country, it shades out other native vegetation and can cause reduced biodiversity. Specifically with Rhododendron ponticum, there is evidence of long-term debilitating effects to the soils in which it is found. The toxins found in the plant seep into the soils surrounding it which increases the acidity, causing reduced growth of other native species. Also, the resulting leaf litter becomes slow-decaying which in turn causes the soils to become infertile and low in nutrients. Over time, this can cause the natural balance of an eco-system to shift and become less encompassing for other biodiverse species.

What can you do?

Rhododendron ponticum can be effectively tackled by a professional invasive species company and we use various tactics dependant on the size of the infestation and requirements of removal.

  • Hand pulling
  • Mulching
  • Herbicide application
  • Stump treatment
  • Excavation

Dependant on the size of infestation, multiple techniques can be undertaken to control or eradicate Rhododendron ponticum from your property.

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