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What is Giant Hogweed?

Giant Hogweed (Heracleum mantegazzianum) is an invasive species that was introduced to Britain in the 19th Century as an ornamental plant. Heracleum mantegazzianum is the name usually used to refer to giant hogweeds but there are as many as four other species in Britain as well as the native hogweed, which is much smaller.

Why is it a Problem?


Giant Hogweed is widespread across the lowlands of the UK and continues to spread rapidly. Each plant produces between 10,000 and 50,000 seeds, this abundance leads to its quick spread despite  the plant being  annuals and only go to seed once. Seeds like moist, fertile soils in partial shade, such as river and canal banks.

The Public

Giant Hogweed poses a threat to human health as it has phytotoxic sap. If this sap comes into contact with skin it can cause severe burns and blistering as it makes the skin extremely sensitive to sunlight. This usually happens within 48 hours of skin coming into contact with the sap.

In the event of skin contact with the sap, the affected area should initially be covered to reduce exposure to sunlight, only uncovering the skin to wash it with soap and water, which should be done as soon as possible. Medical advice should be sought if a rash develops, blistering occurs or you begin to feel unwell. Native hogweed can also cause rashes but these are generally less severe than the damage caused by Giant Hogweed.


Giant Hogweed can grow in large clusters crowding out native species and reducing the natural biodiversity of an area.


Giant Hogweed will die back after seeding, where it has taken over whole areas of bank this can contribute to bank erosion as the bank is weakened without plant roots to contribute to its structural integrity.

Identifying Giant Hogweed

Giant Hogweed can be seen from spring to autumn and favours damp and partially shaded environments.

  • Plants can grow up to 5m tall
  • Large umbrella shaped flower heads that are up to 80cm in diameter with white or occasionally pinkish flowers facing upwards.
  • Leaves are, up to 3m long, sharply serrated and have bristles on the underside.
  • Stems also have sharp bristles, are 5-10cm in diameter and green with purple blotches.

Removal and Control of Giant Hogweed

Giant Hogweed can be controlled by pulling, strimming or with chemicals. It is recommended that professionals are employed to deal with Giant Hogweed due to the danger the plant poses. Those who decide to tackle the plant themselves should pull the plant to limit the spread of the sap and ensure all skin, including the face and eyes, is covered. Beware that any tools may be contaminated with sap and that pulled plants still contain sap.

Always make sure people are aware of the presence of Giant Hogweed.

Report any Giant Hogweed via the PlantTracker website or App.

Need Giant Hogweed information to hand out or refer to when out and about? Download IWA’s Giant Hogweed Fact Sheet, a quick and easy guide to the invasive species.

Other Invasive Species