Urgent warning over ‘UK’s most harmful plant’ due to climate
An expert has explained the action you need to take this weekend
Hogweed plants are already huge this year
A plant with a dangerous property activated in sunlight is set to be ‘largest and most hazardous in years’ this month thanks to the recent weather. Rain followed by hot weather will be ideal growing conditions and a garden expert is urging people to take actioon this weekend.
Giant hogweed ( Heracleum mantegazzianum ) is an invasive plant from the Caucasus Mountains, introduced to Britain in the 19th century as an ornamental garden specimen. It is now widespread across the UK – particularly along riverbanks, footpaths, canal towpaths and the edges of gardens bordering rough ground. It is considered the most dangerous plant in Britain.
Garden expert Luke Newnes at Hillarys said: ” Giant hogweed thrives in wet conditions. This spring’s heavy and prolonged rainfall across the UK has produced exceptional plant growth – with stems reaching up to 5 metres tall and flower heads up to 80cm across. Plants that were knee-height a fortnight ago are now towering over garden boundaries, footpaths and the edges of outdoor spaces where families spend time.
“The plant’s sap contains furanocoumarins – chemicals that strip the skin of its natural UV protection. On their own, they cause no immediate reaction. But once sap makes contact with skin and sunlight hits, a process called phytophotodermatitis begins. The skin loses its UV shield at the point of contact, and even brief sun exposure triggers severe chemical burns.
“With the Met Office projecting a further temperature surge to 30-31C around 17-18 June – this weekend represents the highest-risk window of the year. People who brushed past giant hogweed during this week’s rainy garden clearance may not realise they are already carrying sap on their skin or clothing.
“Critically, the burn response is often painless at first. Blisters typically appear 24-48 hours after exposure, by which point the damage is already done. The affected skin can remain hypersensitive to sunlight for months or even years, causing recurring burns and inflammation with any subsequent UV exposure.”
Why is giant hogweed so dangerous?
The RHS describes giant hogweed as causing severe photodermatitis on contact, with symptoms including burning, blistering, deep pigmentation and long-lasting scarring. In serious cases – particularly where sap enters the eyes – it can cause permanent blindness.
Children are disproportionately at risk. The plant’s dramatic appearance – resembling an enormous cow parsley, sometimes taller than a house – attracts curiosity. Cases of children using the hollow stems as makeshift telescopes or blowpipes have resulted in facial burns and eye injuries requiring emergency treatment. A four-year-old child suffered third-degree burns after contact with the plant at a public park in Bolton.
Pets face the same risk. The Woodland Trust has confirmed that giant hogweed sap causes blisters and burns to animals, with hairless areas of skin – the nose, ears, belly and paws – particularly vulnerable. Sap reaching a dog’s eyes can cause blindness. Dogs running through riverside vegetation or the edges of rough gardens are at significant risk during peak flowering season, which runs through June and July.
The sap does not only transfer through direct contact. It can soak into clothing and remain active on garden tools, transferring to skin hours after the original exposure. Aberdeenshire Council warned in May 2026 that brushing past the plant – without breaking any stems – is sufficient to release sap from leaf hairs and cause burns.
Luke said: “Giant hogweed is the one plant that genuinely warrants the word dangerous – not because it is rare or exotic, but because it is already in millions of neighbourhoods, it looks like something you might pull up without thinking, and its worst effect only appears after you have gone back inside and the sun has come out.
“The combination right now is the worst possible sequence for a homeowner who does not know what they are dealing with. Long periods of rain have pushed growth to exceptional levels. A sharp temperature spike is arriving this weekend. Anyone who has done garden clearance in the last fortnight near rough ground, a riverbank, or an overgrown boundary needs to check what they were handling before they go outside on Saturday.”
Where giant hogweed is most likely to be found
Garden boundaries bordering rough ground, riverbanks or canal towpaths
The highest concentration of giant hogweed in the UK is along waterways, where seeds travel downstream and establish dense colonies along banks. Gardens backing onto rivers, canals, streams or rough pasture are highest risk. The plant does not need to be in your garden – its stems and leaves can overhang boundaries from neighbouring land, and sap can transfer on contact with overhanging foliage.
Areas of recently cleared or disturbed ground
Giant hogweed seeds persist in soil for years and germinate rapidly when ground is disturbed. Recent landscaping, path clearance, or ground preparation near high-risk areas can bring dormant seeds to the surface. Plants that appeared this spring in previously clear areas may be the result of seeds from a parent plant several growing seasons ago.
Public footpaths, parks and verges near water
Giant hogweed is widespread on public land. Paths alongside rivers and canals, the edges of parks and playing fields near watercourses, and roadside verges in rural and semi-rural areas are all known locations. Children and dogs moving through tall vegetation on walks are at risk without any direct garden exposure.
Overgrown corners and the bases of fences and hedges
In garden settings, giant hogweed most commonly appears in neglected corners, at the base of boundary fences, and in areas where vegetation has been left unmanaged over winter. It is frequently mistaken for cow parsley or angelica in its early stages, when it is most likely to be handled without protection.
Four things homeowners should do before clearing hogweed
- Identify before you touch anything
Giant hogweed has distinctive features: coarse, deeply divided leaves that can exceed one metre in width, thick green stems with reddish-purple blotches and coarse white hairs, and large umbrella-shaped white flower heads up to 80cm across. If any tall plant in or near your garden matches this description, do not touch it. Use binoculars to check at a safe distance if necessary.
- Cover up completely for any garden clearance near rough ground
If you need to work near areas where giant hogweed may be present, wear long sleeves, long trousers, waterproof gloves and eye protection. Sap can penetrate thin fabrics. Wash all clothing immediately after, separately, and do not touch your face or eyes during or after the task. Wash any exposed skin thoroughly with soap and water and stay out of sunlight.
- Report any confirmed sighting immediately
Giant hogweed is listed under Schedule 9 of the Wildlife and Countryside Act 1981. It is illegal to plant it or cause it to spread. Report sightings on public land to your local council. Sightings anywhere in the UK can also be logged via the Non-Native Species Secretariat online recording system at nonnativespecies.org. Do not attempt to remove it yourself – professional treatment is strongly recommended.
- Seek medical attention immediately if you suspect exposure
If you believe you or a child has come into contact with giant hogweed sap, wash the affected area with soap and water immediately and cover it from all sunlight – including through windows. Do not wait for symptoms. Go to A&E or call 111 without delay. Tell the clinician you suspect giant hogweed exposure specifically, as the treatment protocol differs from standard burns. The longer the affected skin is exposed to UV light before treatment, the more severe the scarring.
