It burns, blinds and could be in your garden: here’s the lowdown on giant hogweed

We get to the root of the UK’s ‘most dangerous plant’.

We’re lucky in the UK not to face many severe natural threats simply by stepping into our gardens. Well, depending on how bad your hay fever is… But that doesn’t mean we’re completely free of pesky plants that could do some damage. Take giant hogweed – a plant that usually appears in the lineup of usual suspects of ‘dangerous’ greenery we should remain vigilant about.

This towering “invasive alien” (as the UK Government affectionately calls it), has made headlines for several reasons. As reported by the BBC, one man’s encounter with giant hogweed left him with permanent scarring in 2023, and in Scotland sheep have been drafted in as a heroic task force to graze – and ultimately control – infestations of this plant, helping in a way that humans seemingly cannot.

giant hogweed plant growing with blue sky backgroundCredit: Environet

So, what is giant hogweed? Would you know how to spot it growing on your patch, and how worried should you really be about the plant that’s often dubbed ‘the UK’s most dangerous’?

What is giant hogweed?

It’s a toxic relative of carrots, parsley and parsnip

First of all, if giant hogweed is a dangerously toxic, non-native plant, how is it now causing an issue in the UK? According to Nic Seal, founder and managing director of invasive plant specialist Environet, giant hogweed hails from East Asia.

“Like Japanese knotweed, it was imported to the UK as an ornamental plant during the Victorian times and planted in formal gardens and country estates,” he explains. “It has since spread rapidly around the country, with particular hotspots in north London, Greater Manchester and the east coast of Scotland.”

In terms of biology, giant hogweed is part of the Apiaceae family, which includes carrots, parsley and parsnips, according to Fiona Jenkins of trades matching site Myjobquote.co.uk, though this specimen is “substantially bigger” than its relatives.

“Giant hogweed can behave like a biennial or perennial, either dying back after flowering in its second year or coming back annually,” she notes. “Fully grown giant hogweed can reach between 1.5-5m (4ft 9in to 16ft 4in) in height and can spread to a width of 1-2m (3ft 2in to 6ft 5in).”

Flowering usually takes place in the second or third year, she adds. Seal says that the plant’s large, umbrella-shaped flower heads can each produce up to 50,000 seeds a year. All they need is a little help from wildlife, humans, wind or water to spread their misery around the UK.

Where does giant hogweed grow?

It loves to be near water

giant hogweed growing next to a stream in a woodlandCredit: Environet

You may be wondering how such an imposing plant could end up growing near your home. If you live near a riverbank or waterway, you might be closer to giant hogweed than you think.

“Giant Hogweed thrives particularly well along riverbanks and waterways, where the soil is moist and its seeds can easily spread, avoiding seedling competition,” says Seal. “New plants mature in around three years and grow several metres in height, forming dense ground cover and outcompeting native flora to colonise new locations. It’s also often spotted along road verges and railway embankments.”

Jenkins adds that you might spot the plant taking over disused ground, and in gardens and allotments close to infected heathland and woodland.

How to identify giant hogweed

It looks like oversized cow parsley

white flowerheads of giant hogweedCredit: Environet

Giant hogweed is often mistaken for its cow parsley relative, though it’s much larger. But as the former is highly toxic, it’s useful to know the difference between the two.

“Both cow parsley and giant hogweed have very similar flowers, which form in umbrella-like clusters,” says Chris Bonnett, founder of online retailer Gardening Express. “One small difference is that the flowers on cow parsley tend to be smaller than the ones on hogweed.

Seal notes that another giant hogweed lookalike is poison hemlock, which has similar clusters of white flowers and purple-spotted stems – and can be fatally toxic to animals including humans, particularly if ingested.

visible bristles on giant hogweed stemsCredit: Environet

“One of the biggest differences between them and the best way to tell them apart is by their stems. The stems of cow parsley are slim and green, whereas the stem on a hogweed plant is much thicker and will have dark red/purple blotches, with coarse white hair sticking out.”

Seal explains that as giant hogweed is a perennial plant, it dies back in winter and reemerges the following spring.

Seal’s tips for identifying giant hogweed

“Giant hogweed’s leaves are dark green and spiky, forming a rosette of jagged leaves before sending up a flower spike in the second year, and then setting seed in year three.”

“The flower heads are white in colour and held in flat-topped clusters, or umbels, as large as 60cm (2ft) across.”

“The thick, hollow stems are green, with purple or maroon blotches and visible white bristles along the length.”

Is giant hogweed dangerous?

Don’t touch it. Ever.

Sign attached to wire fence warning people of the presence of giant hogweed in the areaCredit: Shutterstock / richardjohnson

If you hadn’t already guessed, giant hogweed is incredibly dangerous. In fact, Seal says it’s “probably the most dangerous plant in the UK”.

There’s good reason for his severity. Coming into contact with giant hogweed can have serious long-lasting effects on your skin, and can go on to limit how you spend your time (particularly if you’re a sun lover).

“It contains furocoumarin, a chemical that reverses the skin’s ability to block out UV rays, causes shocking burns and blisters that may recur for several years and that leave permanent scarring,” Seal explains. “If the sap gets into the eyes, it can cause blindness.”

Safe to say, if you’ve realised you have giant hogweed growing on your property, keep yourself, your pets and any visitors well away from it. Though it is possible to remove the plant from your patch, it’s best to call on professional help.

Removing giant hogweed from your property

There are different ways to tackle to plant

Man in a hazmat suit spraying plants with herbicideCredit: Shutterstock / Fuss Sergey

Removing giant hogweed from your property isn’t a simple task. Jenkins notes that though you’re not obliged to remove the plant, or inform anyone of its presence, most people choose to get rid of it due to its toxicity.

With 50,000 seeds per flower head potentially spreading more toxic plants around your property and neighbouring land, most people want to nip any growth in the bud before it gets out of hand.

“As giant hogweed can grow from its seeds, roots or rhizomes, it needs to be disposed of carefully,” says Jenkins. “For this reason, it is considered controlled waste and needs to be disposed of in a licensed landfill site.

“Polluted ground material, such as soil that giant hogweed has grown in, is also considered controlled waste and must also be disposed of in a licensed landfill site.

“You must not let giant hogweed spread to adjacent land. If this happens, legal action can be taken against you. You also have a legal duty under the Wildlife and Countryside Act 1981 to prevent the plants from spreading into the wild.”

Jenkins says there are a number of ways you can eliminate giant hogweed from your home, with the best solution depending on the size of the plants, their numbers, and the extent of the infestation. Here, she explains the various methods:

Ways to remove giant hogweed

“Spraying should be carried out by a qualified professional who is experienced in the safe handling of herbicides. Glyphosate-based herbicides are considered to be the most effective, and all regulations and conditions for use must be met.

“This method is best used in spring when plants are smaller but will have to be continued for several seasons,” she adds.

“Physical destruction of giant hogweed can be done with machinery such as a tractor-towed flail for large areas or manually for individual plants.

“For manual destruction, full protective clothing should be worn to protect skin from sap exposure. When using machinery, workers and bystanders should be protected.

“Digging out the plant and severing the root should kill the giant hogweed, which should then be left to dry out before disposing of it safely. This method is often used in conjunction with spraying with herbicide.”

“For this method of removal, permission must be sought from the Environment Agency in England or the Scottish Environment Protection Agency in Scotland. Plants and seeds must be buried at least 1m (3ft 2in) below the finished ground level.

“The burial site should remain untouched for 15 years and the location has to be recorded.”

“Taking giant hogweed, its seeds and the soil to a licensed landfill is the quickest way to deal with this toxic plant. All plants and the top 10cm (4in) of soil will need to be removed, as will the soil in the surrounding area to ensure all seeds have been removed.

“The Environmental Protection Act 1990 makes it illegal to dispose of giant hogweed anywhere other than a licensed landfill site.”

How much will it cost to remove giant hogweed?

The cheapest method of removing giant hogweed, according to Jenkins, is by spraying, while excavation and offsite disposal are the most expensive.

“Each situation will be different, and costs will also depend on the size and extent of the infestation,” she says. “It’s advisable to hire a company that is a member of the Invasive Non-Native Specialists Association (INNSA) to deal with giant hogweed to ensure complete peace of mind.

The price of having a specialist remove giant hogweed from your land will depend on the size and extent of the problem.”

giant hogweed growing in a garden next to a wheelbarrowCredit: Shutterstock / lcrms

Survey cost

Jenkins says a surveyor will conduct a Full Residential Invasive Species survey on your property. Costs typically start from £300 + VAT (£360). This amount is payable prior to the surveyor’s visit.

“The survey is a critical first step to ensure all invasives are identified and accounted for in any remediation strategy and subsequent insurance guarantee.”

Jenkins notes a survery of this kind will normally include:

  • A survey of the property by a trained surveyor
  • Full written report of findings
  • GIS mapped out area (data on your hogweed infestation in the form of a map) with a 1mm accuracy (where possible)
  • CAD (Computer Aided Design) site plan showing the location of invasive species in relation to property and property boundary
  • Full photographic evidence of the visit.
Closeup of giant hogweed leavesCredit: Environet

A quote for removing giant hogweed

After the survey, you’ll receive a quotation for an appropriate remediation method (if required).

Jenkins explains some service examples:

  • Five-year Invasive Plant Management Plan (IPMP): Dependent on survey findings, but potentially ranging between £1,900 + VAT (£2,280) and £2,500 + VAT (£3,000) for a small invasion.
  • A typical chemical treatment for a small infestation of less than 30 square metres (323 sq ft) can cost between £2,000 + VAT (£2,400) and £4,000 + VAT (£4,800).

She notes these prices can increase when looking at more severe cases of giant hogweed invasions.

“Companies tend to price each project on a site-specific basis as each situation will be different,” Jenkins warns. “To get an accurate cost for removing giant hogweed from your property you will need to contact a specialist company, have a survey done and get a quotation.”

Rosanna Spence

Written by Rosanna Spence she/her

Updated:

Rosanna Spence has been a journalist for nearly 10 years, reporting on a huge array of topics – from microwaves to cocktails, sustainable buildings, the Caribbean islands and beyond. She’s interviewed chefs at the helm of Michelin-starred restaurants and chatted to countless CEOs about their businesses, as well as created travel guides for experienced travellers seeking life-changing adventures. Throughout her career, she has created content for Business Traveller, i-escape.com, Pub & Bar, BRITA, Dine Out and many more leading titles and brands.

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