Giant Hogweed (Heraculeum Mantegazzianum)


Giant Hogweed is Phototoxic.  Contact with any part of the plant should be avoided at all costs as the smallest amount of the plants sap on human skin, can cause severe blistering and scarring and if it enters the eyes can cause blindness.  The symptoms persist for many years following exposure to UV light (sunlight).

Giant Hogweed, like many of our invasive species, was brought to the UK in the 19th Century as an ornamental plant.  Due to its large production of seeds, it soon spread across the country especially close to rivers where it can be transported easily and quickly.  This means Fisherman often come into contact with the plant often getting serious Giant Hogweed burns.

Giant Hogweed is a true giant of a plant when fully mature and cannot, when at this growth stage, be confused with any other species due to its size.  When flowering, in late June – Mid July, it reaches between 2 - 4m in height bearing an umbrella shaped flower head of approximately 80cm in diameter, producing 1,500 – 100,000 seeds.  Once the seeds are set, the plant then dies back.  The leaves often grow to 1 – 1.5m or more in size and have serrated edges.  The stem of the plant is thick, hairy looking and covered in green and purple speckles.


Giant Hogweed is Phototoxic, meaning that it produces a toxic sap that is activated by Sun light.  Contact of the sap with human skin causes Phytophotodermatitis also known as Giant Hogweed burns.  These burns blister, leaving scars on the skin.  If the sap comes into contact with the eyes, then blindness can occur.  The symptoms can re-occur year after year, activated when the skin is under direct sunlight.

It can often be confused with its smaller species, Hogweed.  Hogweed is a smaller plant only growing to 1.5m – 2m with rounder leaves with smooth edges.  Can look very similar to immature Giant Hogweed.  If unsure DO NOT TOUCH.

Due to the plants toxicity and invasive characteristic it is one of only two plants listed in the Wildlife and Countryside Act 1981 making it an offence to plant or cause Giant Hogweed to grow in the wild.

If you see Giant hogweed, report it using the Plant tracker app from the environment agency.  It can be downloaded here.

The best way to control Giant Hogweed is by herbicide application before the plant has gone into seed.  If the plant has gone into seed, then the seed heads need to be removed by a specialist team wearing the correct personal protective clothing.  The seed heads are then double bagged and disposed of as “controlled waste.”

If you have, or think you may have Giant Hogweed and would like a free, no obligation quote to implement a management plan, please do not hesitate to contact us today.