Giant hogweed (Heracleum mantegazzianum) is a problem plant with a capital P. Originally introduced from South-west Asia as an ornamental plant, it quickly escaped from gardens and spread at an alarming rate. The earliest documented occurrence in Britain is found in the Royal Botanic Gardens Kew Seed List of 1817 where giant hogweed, then known as Heracleum giganteum, was listed among seeds sent to Kew by the Russian Gorenki Botanic Gardens.
Giant hogweed is striking in appearance, with flowering stems up to 3.6m (12 ft) tall high. However, it is recognised as an invasive species that crowds out native species, particularly on riverbanks and, once established, is difficult to control as it seeds prolifically.
It is a biennial, so you can prevent the plant from spreading by removing the flower heads before it sets seed. Always wear gloves and make sure your arms and legs are covered when handling these plants. Giant hogweed is a health hazard, as its sap is an irritant and can cause severe blistering of the skin on exposure to sunlight.
The Wildlife and Countryside Act 1981 (amended) lists giant hogweed on Schedule 9, Section 14, which means it is an offence to cause giant hogweed to grow in the wild in England and Wales (there is similar legislation in Scotland and Northern Ireland). It may also be the subject to Anti-Social Behaviour Orders where owners of land infested with giant hogweed can be required to remove the weed or face penalties.