Usually biennial, giant hogweed forms a rosette of serrated, deeply divided green leaves in its first year. Eventually these reach up to 1.5m (5ft) wide and 3m (10ft) long. In its second year, it sends up thick, bristly, green and purple-blotched stems that are hollow inside. These can reach 5m (16ft) or more in height.  

The stems hold umbels (umbrella-like clusters) of upward-facing white flowers; the umbels can be as large as 60cm (2ft) across. Flowers are followed by masses of penny-sized, paper-thin seeds with distinctive dark brown stripes. Underground, giant hogweed grows from a pale, swollen

A large, tapering, central root that grows downward. It's typically thicker and deeper than the other roots, allowing access to water and nutrients from deeper in the soil. Plants with taproots include dandelions, carrots and parsley.

At its full height, giant hogweed is not easily confused with other plants. However, in early growth, or where plants are stunted, it can be confused with other common umbelliferous plants like cow parsley and common hogweed. The former has fern-like foliage and flowers earlier in the year; the latter has more rounded leaves, no purple blotching on the stem and is smaller in stature, growing up to 2m (6ft) tall.

RHS members can send photos to the Gardening Advice service for help identifying umbels in their garden.

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Cow parsley has softer, fern-like foliage

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Common hogweed is much smaller in size

Owing to its fast-spreading nature and large size, giant hogweed can quickly shade and outcompete native (and other) plants and is therefore considered to be a weed. It appears on the Wildlife and Countryside Act 1981, Schedule 9 list of non-native invasive species and the Non-native Species Secretariat (NNSS) list of Species of Special Concern, meaning there are restrictions on growing, cultivating, selling and transporting it.  

If giant hogweed is already growing in your garden, this is not considered an offence, though it is recommended that you control or remove it. However, you must not intentionally plant it or cause it to spread.   

Aside from its invasive nature, giant hogweed poses a serious risk to human health. All four species contain high levels of furanocoumarins – chemicals which make the skin very sensitive to sunlight. Touching giant hogweed with bare skin can lead to severe photodermatitis, with symptoms including burning, blistering, pigmentation and long-lasting scarring.

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Contact with giant hogweed causes blistering of the skin

Here are our answers to your most common questions about dealing with giant hogweed.

How invasive is giant hogweed? 

Giant hogweed produces masses of seed, up to 50,000 per plant, and these are dispersed over short distances by the wind and over much longer distances if they land in waterways. Gardens bordering open countryside or wasteland are most likely to find giant hogweed appearing, but seed may also be spread by soil stuck to shoes and tools. 

Its seed has a high germination rate, and most germinate in the spring after dispersal, so plants can quickly colonise new ground. Seedlings initially produce a taproot, helping them get established quickly, and before long their large size helps them to outcompete neighbouring plants.

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Giant hogweed produces masses of seed

Do I need to get rid of giant hogweed? 

It is not an offence to have giant hogweed growing in your garden, as long as you take steps to stop it spreading. However, as it poses a serious health risk to people and pets and can outcompete many border plants, it is good practice to remove it.

You do, however, need to remove giant hogweed if you are ordered to do so. Section 14(4A) of the Wildlife & Countryside Act enables an environmental authority to take action to enforce the control of invasive non-native species. You may be asked to enter into a species control agreement, where you agree to control or remove the plant, or served a species control order to do so. If you fail to comply with this, the environmental authority may carry out the work themselves and recover costs from you. They may also prosecute and if found guilty, landowners face imprisonment and/or a fine.   

Local authorities and the police also have powers under the Anti-Social Behaviour, Crime and Policing Act (2014) to issue Community Protection Notices to landowners who are failing to control giant hogweed and who are acting unreasonably in a way that affects the quality of life of their neighbours.

What is the easiest way to kill giant hogweed? 

Given how dangerous it is to handle giant hogweed, the safest way to remove it is to hire a specialist weed removal company. They will have appropriate PPE to protect themselves and are likely to be a registered waste carrier and so legally able to dispose of giant hogweed correctly (see below). The following organisations have lists of contractors who specialise in the removal of invasive plants:

PCA (Property Care Association) Invasive Weed Control Group 
Invasive Non-Native Specialists Association 
The British Association of Landscape Industries (BALI)  
Trustmark Government Endorsed Standards

Small populations of giant hogweed can, however, be tackled yourself. Ensure you wear gloves and cover as much skin as possible. Be aware that plant material can still cause skin damage several hours after being cut down or dug up. Sap on clothes and tools can also cause skin damage, so handle these carefully and wash them well.  

Wash any skin that touches the plant immediately, keep it out of sunlight and seek medical advice.  

If tackling the removal of giant hogweed yourself, you have the following options: 

• Hoe off seedlings – this is a good way to stop individual plants becoming a colony and is important if established plants were not deadheaded in time. Hoe promptly in spring before seedlings develop their taproot and do so on a warm, dry or windy day, so exposed roots dry out quickly.  
• Pull up young plants – wearing gloves, pull up plants in May once they have reached a reasonable height but before they start flowering. This is easiest if the soil is moist. For larger plants it may be necessary to loosen the soil and lever out roots using a border fork. 
• Deadhead promptly – allow established plants to produce a flower spike, then trim the stem down to ground level before the flowers fade. At this point, giant hogweed is less likely to survive being cut back. Bear in mind that some species are perennial and preventing them from setting seed will not reduce populations quickly.  
• Deadhead carefully – if removing plants that have already begun to set seed, cover the head with a bag before you start, to collect seeds and limit their dispersal.

How should I dispose of giant hogweed? 

Giant hogweed is classified as 'controlled waste' under the Environmental Protection Act (Duty of Care) Regulations. If possible, destroy plants on site. If removal is necessary, the Environment Agency needs to be informed and you must use a registered waste carrier and an authorised disposal site. Contact the Environment Agency or your local council for information on authorised sites. If you use licensed contractors, ensure they use registered disposal sites and provide copies of waste transfer permits. 

The following government websites provide more information: 
Treatment and disposal of invasive non-native plants: RPS 178  
How to stop invasive non-native plants from spreading  

You should not add giant hogweed (and soil that may contain its roots or seeds) to your home compost, council green waste or household waste bin.

Should I use weedkiller? 

The RHS does not support the use of weedkillers and recommends that alternative control methods are used. However, when invasive plants are a threat to biodiversity and gardeners struggle to control them with cultural methods, targeted use of regulated weedkillers may be an option. Garden centres and large retailers selling weedkillers have trained staff who can advise on suitable products for your needs.