Giant hogweed

Giant hogweed facts

Scientific name: Heracleum mantegazzianum

Family: Umbellifer

Native to: Central Asia

Type: Typically biennial, but can be perennial

Which species eat it? None

Location: On land, usually near larger canal banks, but can be found near any stretch of water. Widespread across the UK

Giant hogweed in Britain

In 1820, giant hogweed was intentionally planted in gardens close to rivers and ponds due to its striking visual presence. Eight years later, it was first recorded in the wild in Cambridgeshire.

As a result of its negative impact on native wildlife and habitats, and its health risk to humans, giant hogweed is now listed under Schedule 9 of the Wildlife and Countryside Act 1981, meaning it is illegal to cause it to grow in the wild.

Why is giant hogweed a problem for canals and native wildlife?

Reaching over five metres tall when fully grown, giant hogweed keeps other plants in the shade and prevents the sunlight from reaching them. This increases the risk of bank erosion when the weed dies off in the winter, exposing bare areas where other plants would normally grow.

It also reduces suitable habitat space for a variety of wildlife, including the endangered water vole.

Controlling its spread is challenging. Giant hogweed depends entirely on seed dispersal to spread, and can self-fertilise. Its flowers can hold as many as 50,000 seeds, which are paper thin and about the size of a penny.

The majority fall within four meters of a parent plant and create densely populated areas, but a large proportion also float down waterways, enabling it to grow elsewhere.

Is giant hogweed dangerous to humans?

Giant hogweed is harmful to humans. Coming into contact with any part of this plant (even loosely brushing past it) can burn skin and cause lifelong issues when exposed to sun. This means it is considered to be a serious and significant danger to public health.

You should not attempt to remove giant hogweed from anywhere yourself. It should only be treated by qualified, suitably protected contractors.

If you accidentally come into contact with giant hogweed, you should seek medical advice as soon as possible.

What does giant hogweed look like?

Whilst growing, giant hogweed is similar to cow parsley and our native common hogweed, but at full height it is much larger and easily distinguishable.

It has sharply serrated leaves, which can grow up to three metres long and have bristles on the underside. The plant stems can grow up to five meters tall and 10cm wide, and are also usually covered with sharp bristles.

The flowers, which can stretch to 80cm wide, are white and umbrella shaped.

How to report invasive species

If you see an invasive, non-native plant species on one of our canals or rivers, please contact us online or call us on 0303 040 4040 and we'll check if it is already included in our treatment schedule.

Other invasive species on our canals