Rhododendron ponticum: The plant haunting our wild spaces

A Victorian favourite turned invasive threat

Rhododendron ponticum is an evergreen bush native to Spain, Portugal and the Caucasus region. Its beauty made it a garden favourite for Victorians, who popularised it in the UK in the nineteenth century. It was planted in country estates that were later abandoned during economic collapses, allowing it to run wild and spread uncontrolled.

Conditions in the UK are ideal for R. ponticum to thrive, our Senior Curator of British and Irish Seed Plants Chris Dixon says. The habitats where it grows are surprisingly similar to those in Spain and Portugal. “A lot of rainfall, very wet soil and acid conditions of bogs and woodlands,” he explains.

Originally the cold winters in the UK would have posed a problem but, according to Chris, breeders made it frost hardy by hybridising it with North American species, making it perfectly suited to UK conditions.

Rhododendron’s deadly impacts

Rhododendron ponticum may look pretty, but it poses a hidden danger.

For pollinators, the story is complicated. The bright flowers’ nectar contains toxins that can be deadly to European honeybees. However, when they’re able to mix it with other nectar sources, colonies usually survive. Some bees, including certain bumblebees, seem to handle the toxins better.

In places where rhododendrons dominate the nectar supply, such as the Black Sea region of Turkey and the Himalayas, bees can produce the notorious ‘mad honey’. In large doses, this honey is toxic to humans, causing dizziness, blurred vision and low blood pressure.

Fortunately, in the UK the plants produce lower levels of toxin than in their native habitat and the honeybees tend to feed on other flowers. No poisoning events have been reported here, so you needn’t worry about your afternoon tea ending like it does in the 2023 film A Haunting in Venice.

Bees and humans aren’t the victims of R. ponticum we should be concerned about. Once choking the grand estates of Victorian Britain, this plant still overpowers gardens today. This Invasive Non-Native Species (INNS) kills almost every single plant it shares space with, making it one of Britain’s most destructive plant species.

According to the Woodland Trust, INNS play a key role in 60% of recorded global plant species extinctions and are solely responsible for 16%. These aren’t numbers we want to increase, especially in a country where more than half of plant species are already non-native.

The impact of R. ponticum on the local vegetation can’t be overstated. It grows strongly and spreads quickly. One single bush can produce millions of seeds, which then disperse easily by wind and water. Its branches can also take root by touching ground.

Its fast propagation results in what Chris describes as “a thick canopy of evergreen leaves” that easily covers anything next to it. “No light gets past all that,” Chris says, “so anything that might have grown up underneath just can’t.”

Moreover, R. ponticum is a known carrier of diseases including Phytophthora ramorum, a fungus-like organism that can kill more than 150 plant species.

The temperate rainforests in the west of Scotland have been heavily affected by R. ponticum. These woodlands, filled with birch, hazel, ash, oak and pine trees, capture huge amounts of carbon, but are now being choked by rhododendron.

This invader is spreading elsewhere too, from the uplands of North Wales to the Derbyshire valleys of the Peak District.

How to remove it and what to plant instead

Rhododendron ponticum is notoriously hard to remove once established. Hand cutting, pulling and uprooting as well as the use of herbicides are common methods to tackle it. On a large scale, a combination of some or all of these, as well as follow-up controls, are necessary to ensure it’s fully removed.

Despite all this and the fact there’s many alternatives to R. ponticum, it’s still being sold in garden centres, plant nurseries and on the internet. In the UK, it’s not illegal to grow it in your garden, but it’s an offence to plant it in the wild or to let it spread there.

In your own garden, it’s best to replace it if you can, especially if you’re near a wildlife area. There are plenty of non-invasive varieties of rhododendron to choose from instead. For example, Rhododendron ‘Cunningham’s White’, ‘Furnival’s Daughter’ or Azalea ‘Vuyk’s Scarlet’ can add that touch of colour to your garden without threatening it or the surrounding area.

To dispose of R. ponticum, you can take it to your local recycling centre, but make sure you confirm with them beforehand that they’ll accept it. Alternatively, you can burn it on your property, but check local byelaws first or ask a registered waste carrier to take it. You shouldn’t put it in your garden waste or use it for composting, as it can infest areas where the compost is used.

You can also support organisations working to control R. ponticum, including the Alliance for Scotland’s Rainforest, Pembrokeshire Coast National Park and Trees for Life.

The National Trust for Scotland offers a free Community Garden Scheme to remove R. ponticum and replace it with other plants. Meanwhile, the Woodland Trust is asking the UK government to increase the invasive species biosecurity budget.

Every bit of help counts towards fighting INNS, but there’s a bigger lesson to be learned from the arrival and settlement of R. ponticum.

When the Victorians first brought it into the country, they never imagined this beautiful flower would threaten the same landscape they were trying to enhance. Similarly, those who’ve more recently bought it for their gardens may not have known its history and risk.

The lesson is clear! Planting native wildflowers is the safest choice. However, non-native plants are better than no plants at all, but make sure they’re not invasive.

We breed plants because we want to feel connected to nature. Planting native trees and shrubs that attract wildlife is a great way to do this.

You can buy a wildflower mix from a supplier that specialises in native British wildflowers to grow a wildflower pot for pollinators. You can also stop mowing your lawn for a while so plants already present have the chance to grow and make it better for wildlife.

From clovers and daffodils to honeysuckles and wild roses, there’s no shortage of beautiful, wildlife-friendly plants to grow. Your garden can still look stunning if you swap out the botanical villains that haunt our wild spaces for native heroes that help them bloom.

By choosing native plants, or at the very least non-invasive species, you’re helping protect the landscapes that R. ponticum continues to threaten.