Giant hogweed in Sussex: Warning over UK's 'most dangerous plant' as interactive map shows where it grows

A warning has been issued about the spread of Giant Hogweed around Horsham, Midhurst, Balcombe and Gatwick - with an interactive map showing the most problem areas.
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The GB non-native species secretariat (NNSS) says Heracleum mantegazzianum, more commonly known as Giant Hogweed, is a member of the cow-parsley family with flowering stems typically 2-3 m high bearing umbels of flowers up to 80 cm in diameter. The basal leaves are often 1 m or more in size.

It warns: “The sap can sensitize human skin to ultra-violet light, leading to severe blisters. Affected skin may remain sensitive for several years. The plant is also a vigorous competitor, producing almost pure stands which exclude native vegetation and hinder anglers.

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“It is especially abundant by lowland streams and rivers, but also occurs widely on waste ground and in rough pastures. It grows on moist fertile soils, achieving its greatest stature in partial shade. In more open grassland, flowering may be delayed by repeated grazing.”

The map shows the locations of Giant Hogweed across the countryThe map shows the locations of Giant Hogweed across the country
The map shows the locations of Giant Hogweed across the country

Where it is reported on roads and pavements the weed is dealt with by West Sussex County Council.

Its website says: “We use specialist treatment methods for harmful weeds, such as Giant Hogweed and Japanese knotweed. If you notice any of these weeds on the highway, please report it online. If the weeds are located on private property, then these are the responsibility of the landowner.”

And it adds: “Please report online or phone 01243 642105 if you spot:

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significant areas of weeds in urban areas that are causing a hazard, such as large cracks or very uneven areas of pavement noxious weeds, for example giant hogweed and Japanese knotweed.”

Places where Giant Hogweed has been reported in West SussexPlaces where Giant Hogweed has been reported in West Sussex
Places where Giant Hogweed has been reported in West Sussex

Giant Hogweed has been spotted around West Sussex many times, and now, WhatShed has produced a live interactive map to track the spread of the plant.

It shows the area north of Horsham between Kingsfold and Rusper is a particular problem, with reports of Giant Hogweed along the Sutton Mole Valley Line.

It is also marked around Loxwood and the River Arun, near Tanbridge House School in Horsham and along the A264 between the Robin Hood Roundabout and the Rusper Roundabout.

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The map shows some at Warnham, near the A281 by Mannings Heath, as well as Balcombe and Midhurst.

The weed has also been reported at Gatwick Airport according to the map.

Giant Hogweed facts

It is a close relative to cow parsley.

It has thick, bristly, reddish-purple stems and can reach over 3m (10ft) in height.

The flowers are white in a flat-topped clusters that can be as large as 60cm (2ft) across.

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Giant Hogweed was originally brought to Britain from Central Asia in 1893.

It commonly grows on riverbanks and wasteland.

Its leaves, stems, roots, flowers and seeds contain toxic components which can be transferred by contact and make exposed skin extremely sensitive to sunlight.

What should I do if I touch it?

After coming into contact with the plant, the burns can last for several months and the skin can remain sensitive to light for many years.

The NHS advises: “If the sap of the Giant Hogweed comes into contact with your skin, it can cause severe, painful burns and make your skin sensitive to strong sunlight.

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“If you touch a Giant Hogweed, cover the affected area, and wash it with soap and water.

“The blisters heal very slowly and can develop into phytophotodermatitis, a type of skin rash which flares up in sunlight. If you feel unwell after contact with Giant Hogweed, speak to your doctor.”