Giant Hogweed

Heracleum mantegazzianum

Information

Size: Over 3m tall

Native to: Caucasus Mountains and Central Asia

Introduced to the UK: As an ornamental plant in the 19th Century; it escaped and naturalised in the wild.

When To See

Usually biennial, it forms a rosette of leaves in the first year and sends a flower spike in the second year and then sets seed. However, giant hogweed often behaves as a perennial and comes up every year. Flowers appear in June and July.

Habitat

It can be found throughout much of the UK. It especially colonises river banks, as its seeds are transported downstream by moving water. It can also be found on waste ground, around rubbish tips, and on roadside verges. It crowds out native plants by forming large dense colonies.

How To Identify

The flowers are white and face upwards held in umbels (flat-topped clusters), similar to the related cow parsley. It can grow over 3m tall and can spread up to 2m wide. It has large lobed, jagged leaves with hairy underside. The stems are green with purple marks and stiff white hairs.

Giant hogweed sap is phototoxic, which means if it can burn and blister skin in the presence of sunlight.

How It’s Treated

Digging out and suppressing with mulch in very small quantities, otherwise most often treated chemically with approved herbicides. Full protective skin and face covering is always used when removing giant hogweed due to the risk of contact with the phototoxic sap.  

In flower with large white umbels

Giant hogweed can grow up to 3m tall

How it looks as it’s dying off

Seen It?

Been kicking about near your local river or burn and come across one of these species? Not sure? Share it with us at riverlife@forthriverstrust.org, we enjoy chatting about invasive species with you.