Giant Hogweed

Introduced to the UK as a garden ornamental in the 1800’s from South West Asia and a member of the carrot family (Apiaceae). Giant Hogweed produces plants lasting several years and is much larger than our native hogweed / cow parsnip (Heracluem sphondylium). In the summer large white umbrella-like flowers emerge producing thousands of seeds that easily spread, either persisting in the soil for several years or forming new infestations the following year.

Giant Hogweed is now widespread across the UK invading habitats such as riverbanks, roadsides and waste ground. The sap of this highly invasive weed contains chemicals called furanocoumarins which can cause severe and painful skin blisters on humans as well as being toxic to grazing animals. The invasive, persistent and harmful nature of this weed has led to it being included in legislation such as Schedule 9 of the Wildlife & Countryside Act 1981 and classified as a controlled waste (Environmental Protection Act 1990). 

Successful management within a site requires controlling the weed, seed and movement of soil. Contaminated soils can be removed offsite by a licenced waste carrier ensuring the removal of all life stages. Alternatively, the weed can be managed using herbicides during the spring and early summer (i.e. before flowering) over several seasons until the seed-bank has been depleted.  What is difficult is controlling re-establishment if a neighbouring infestation is unmanaged, care should be taken to identify possible sources.