There have been reports in the news lately about the dangers of giant hogweed. Should you be worried?
Giant Hogweed (Heracleum mantegazzianum) was introduced into the UK by the Victorians as an ornamental plant for lakesides and gardens, but it wasn’t until the 1970s that it gained notoriety. At this time, many children who tried to use the stems to make pea-shooters or telescopes developed blisters as a result of touching the plant’s sap.
Giant Hogweed is part of the carrot family and is found throughout Bedfordshire, Cambridgeshire and Northamptonshire, especially on riverbanks and wasteland. It is often mistaken for our own native hogweed (Heracleum sphondylium), which will be a familiar plant to gardeners and ramblers in the UK. Our native hogweed is similar in appearance, but much smaller (generally under 2 metres) with darker green leaves. It can cause rashes and other skin complaints but reactions tend not be as severe as with the larger species.
- A giant plant with deeply divided, light green spiky leaves
- The plant appears in March as a rosette of leaves
- As the season progresses, a stout stem, often with purplish blotches, pushes upwards, reaching perhaps 5 metres (15 feet) in July
- It produces a flat topped umbrella-like clusters of white flowers as large as 60cm (2ft), with several subsidiary flower heads. These flower heads have many individual white florets.
- The plant takes 3-4 years to reach maturity, then flowers and dies
Skin contact with toxic components in the leaves, stems, roots, flowers and seeds produces a reaction in almost everyone. The toxins alone do not cause burning – but they make skin sensitive to sunlight, which can then cause rashes, burns and severe blistering. Blisters often occur 24 to 48 hours after exposure, and dense pigmentation is visible after three to five days. Damaged skin will heal very slowly; leaving residual pigmentation that can develop into phytophotodermatitis – a type of dermatitis that flares up in sunlight and for which there is no straightforward treatment. The degree of symptoms will vary between individuals, but children are particularly sensitive and the blistering can recur for many years after the original incident
Unfortunately a giant hogweed plant can produce up to 50,000 seeds per year which are easily transported along rivers and other watercourses. It is important to stop it seeding though there is no legal obligation in the UK to remove or control the plants. Neither gardeners nor conservationists should attempt to cut the plant down (exposing its sap). Protective clothing should be worn when dealing with giant hogweed, and ideally only a specialist contractor should undertake its safe removal. More information on the identification of giant hogweed can be found on the Non-native Species website. Information on the control of Giant Hogweed can be found on the RHS website.
Cut stems and leaves remain active for several hours. The NHS says anyone who touches giant hogweed should wash the area of skin with soap and water, and keep it covered.