Here is a handy guide for recognising an unwanted visitor known for making an appearance in our gardens and green spaces, as it has already been spotted around the Watford area multiple times this summer.

Giant hogweed is not native to the UK – it was first introduced as an ornamental in the 19th century when it escaped and naturalised in the wild.

The sap of the invasive plant can cause burns if it contacts your skin and when exposed to the sun it can blister badly.

@alnwickgarden DON’T touch Giant Hogweed, DO follow us on Tik Tok 💖🌿 📍The Poison Garden, Alnwick Northumberland #poison #gianthogweed #hogweed #poisongarden #fyp #fypシ #viral ♬ Witch Familiar (Classical) [Classic](143628) - dice

Giant hogweed around Watford

The hazardous invasive plant has been spotted multiple times in and around Watford in recent months as conservation worker Sandy Belloni, who runs the local action group Community Connections Projects CIC, has been tackling an infestation between the M1 and A41 near Bushey.

Mr Belloni has first raised the issue with National Highways in 2021 and has continued to pressure them to spray the plants to stop them flowering.

Sandy Belloni said he is losing faith in National Highways over an infestation which has survived since at least 2021.Sandy Belloni said he is losing faith in National Highways over an infestation which has survived since at least 2021. (Image: Sandy Belloni) In June, walkers were also warned to avoid a giant hogweed plant on the Grand Union Canal towpath near Apsley Lock after it was treated, although it was thought to be an isolated plant.

The Giant Hogweed, before it was sprayed. The Giant Hogweed, before it was sprayed. (Image: Contribution) But how do you spot giant hogweed near you? Here is what you need to look out for and what to avoid.

How to identify giant hogweed

Giant hogweed is often compared to looking like an “enormous” cow parsley plant.

When it's fully grown, it can reach heights of between 1.5m to 5m and have a spread of between 1 and 2m.

“It forms a rosette of jagged, lobed leaves in the first year before sending up a flower spike in the second year and then setting seed,” adds the Woodland Trust.

Watford Observer: Have you had giant hogweed removed from your garden?Have you had giant hogweed removed from your garden? (Image: Getty)

Here is how to identify giant hogweed according to expert Helen Keating:

Stems

“Green and often with purple blotches and stiff, white, britly hairs. Stems are hollow with ridges and have a thick circle of hairs at base of each leaf stalk.”

Leaves

“Huge, up to 1.5m wide and 3m long and is deeply divided into smaller leaflets. It looks a bit like a rhubarb leaf, with irregular and very sharp or jagged edges - which has given rise to one of its other common names - wild rhubarb. The underside of the leaf is hairy.”

Flowers

“Appear in June and July. They are small and white (or slightly pink) and are clustered on umbrella-like heads known as umbels that can reach a diameter of 60cm. All the flowers on the umbel face upwards.”

Seeds

“Dry, flattened, and oval. Almost 1cm long with tan with brown lines extending 3/4 of the seed length.”

How do you tell the difference between hogweed and giant hogweed?

Although common hogweed is “very similar-looking” to giant hogweed, it is much smaller.

Poisonous Plants Found in the UK

Helen explains: “Its stems aren’t blotchy like those of giant hogweed (their colour graduates smoothly from green to purple) and are ridged, hollow and hairy.

“Common hogweed only reaches a maximum height of 2 metres (6ft 7) and the symmetrical flower heads only reach 20cm across.

“Its seeds are much smaller and lighter than those of giant hogweed, and the leaves are less jagged and more rounded at the edges than giant hogweed.”