What is giant hogweed? How to spot toxic plant that can cause burns

Giant Hogweed. (Getty Images)
Experts are warning about the dangers of Giant Hogweed. (Getty Images)

We may still be waiting for the UK summer to officially get started, but experts are warning of a record invasion of Giant Hogweed - as the mild and wet weather earlier this year has seen it boom earlier than ever.

The sap of the invasive and toxic species - dubbed UK’s "most dangerous" plant can cause highly painful burns, which blister within 48 hours, often hospitalising people and leaving them with permanent scars.

Experts say that this year's early showing of Giant Hogweed could have been caused by 2024's spring showers - with March seeing rainfall levels up by 27%.

From how to spot it to, what to do if you touch the sap, here's everything you need to know about Giant Hogweed.

Giant Hogweed is a member of the carrot family and is a close relative of the commonly found cow parsley you find flowering in hedgerows in late spring to early summer.

The plant, known in Latin as Heracleum Mantegazzianum, can grow up to six metres tall.

The invasive species is not native to the UK, and according to the Woodland Trust it was first introduced as an ornamental in the 19th century when it escaped and naturalised in the wild.

“Like many invasive species, such as Japanese Knotweed and Himalayan Balsam, it was brought to the UK as an architectural oddity, but now it has escaped and, without any natural enemies, it grows into dense colonies, especially along watercourses," explains Keith Gallacher, director of Complete Weed Control.

“It is part of the Apiaceae family, which includes carrots, parsnip, cumin, coriander and parsley, but its dense foliage prevents light reaching the soil underneath, killing off native plants and leading to rapid soil erosion.”

Giant Hogweed in the countryside. (Getty Images)
The toxic plant as a sap that can cause burns and blisters when exposed to sunlight. (Getty Images)

According to Ted Bromley-Hall, gardening expert at IBRAN its sap is known to contain a highly concentrated dose of an extremely irritating phototoxic compound called furanocoumarin.

Contact with this sap can cause extreme reactions including blistering and scarring and, in some extreme cases, anaphylaxis.

"The reaction is triggered when the sap makes contact with the skin and is exposed to sunlight," he adds.

There is also a risk of potential blindness if the plant comes into contact with the eyes.

The easiest way to spot the difference between a giant hogweed and other species like cow parsley, which looks similar, is via the stem.

"Giant Hogweed plants have reddy-purple splotches along the stem and coarse white hairs at the base of the leaf stalk," Bromley-Hall explains.

"A fully grown giant hogweed can reach 3 to 4.5 meters tall with 100-150cm wide leaves notable for having deep incisions and serrated edges," he adds.

The Woodland Trust says other ways to spot the toxic plant is via its leaves which are huge, up to 1.5m wide and 3m long, and deeply divided into smaller leaflets.

"It looks a bit like a rhubarb leaf, with irregular and very sharp or jagged edges - which has given rise to one of its other common names - wild rhubarb," the Woodland Trust states.

"The underside of the leaf is hairy."

Common hogweed is very similar-looking to giant hogweed but is much smaller.

"Its stems aren’t blotchy like those of giant hogweed (their colour graduates smoothly from green to purple) and are ridged, hollow and hairy," the Woodland Trust adds.

Woman picking Cow's Parsley. (Getty Images)
Giant Hogweed is often confused for Cow's Parsley. (Getty Images)

If you are working in an area where the plant is growing, Bromley-Hall advises ensuring you are wearing adequate protective clothing including eye protection and gloves.

The Woodland Trust says the best way to avoid injury is to familiarise yourself with the plant and avoid contact with your skin.

"Brushing through patches of giant hogweed and exposing yourself to plants that have been cut might cause you to get sap on your skin," it adds.

The sap of giant hogweed is toxic and can cause burns and irritate the skin.

"It prevents the skin from the ability to protect itself from sunlight," explains Abbas Kanani, superintendent pharmacist at Chemist Click.

"Serious blistering and swelling typically occurs within 24 hours of the skin making contact with it and can worsen if the area is overexposed to the sun."

If you come into contact with Giant Hogweed Kanani recommends washing the affected area with cold water and soap and any clothing that may have the sap on it immediately.

"You should also avoid sunlight for at least 48 hours and do not burst any blisters that appear," he adds.

"Seek medical advice from your doctor or pharmacist as soon as you can.

"Nonsteroidal anti-inflammatory drugs, such as ibuprofen may help to relieve the pain and soreness and applying a hydrocortisone cream can help with the itching, however it is important to contact your doctor especially if you feel unwell after contact with giant hogweed."

While it may look pretty, it’s advised to remove the plant as soon as you see it, as it poses a significant risk to individuals unaware of its harmful effects.

To control giant hogweed in your garden, London Rubbish Removal Company suggests focusing on preventing seed formation to stop its spread.

"Removing the plant entirely is the most effective method," it adds. "Always wear protective gear when handling the plant, and cut it just below the growing point underground.

"If needed, apply herbicide at the start of the growing season in May."

Additional reporting SWNS.