Giant Hogweed Surveys

What is Giant Hogweed?

Giant hogweed, known scientifically as Heracleum mantegazzianum, is a large, fast-spreading plant native to the Caucasus Mountains. It was brought to Britain in the nineteenth century for use as an ornamental plant, but it had escaped into the wild by 1828.

It has since spread extensively across the UK, colonising riverbanks, roadsides, waste ground, railways, parks and abandoned areas throughout England, Scotland, Wales and Northern Ireland.

This invasive weed belongs to the Apiaceae group: it’s a member of the parsley, parsnips and carrot family and is capable of producing between 20,000 and 100,000 seeds per plant.

More than 90% of seeds produced by a parent plant can germinate, and the seed heads are dispersed by wind and watercourses, enabling giant hogweed seedlings to grow across both short and long distances.

How to Identify Giant Hogweed

Giant hogweed is sometimes confused with common cow parsley or Queen Anne’s lace, but several features set it apart.

While it resembles giant cow parsley, giant hogweed grows up to an impressive size – 14 feet in height – its flower spike making it substantially larger than most other roadside plants.

Its hollow stems are thick and covered in coarse white hairs with distinctive purple blotches on the leaf stalk, and its deeply lobed leaves can reach up to five feet in width with sharply jagged edges.

Giant hogweed forms dense patches, often among other plants, and grows large, dense umbrella-like clusters of greenish-white flowerheads.

Is Giant Hogweed Dangerous? 

Yes, giant hogweed poses a real risk to human health. Giant hogweed sap contains chemical compounds called furanocoumarins, which are toxic to humans.

If sap comes into contact with bare skin and is then exposed to sunlight, it causes a severe reaction known as phytophotodermatitis, resulting in serious skin inflammation, painful burns, blistering and long-term scarring.

In some cases, contact with the eyes can lead to temporary or permanent blindness. Symptoms may take between 24 and 48 hours to appear.

Anyone who comes into contact with giant hogweed should avoid further sun exposure and seek medical advice promptly. If you get sap on your skin, shower immediately. Protective clothing and eye protection should be worn when working near giant hogweed.

This invasive plant also poses environmental risks. During its life cycle, its dense growth can displace native vegetation, reduce biodiversity and destabilise riverbanks by leaving bare, exposed soil when it dies back in winter.

Giant Hogweed and the Law

Giant hogweed is listed in Schedule 9 of the Wildlife and Countryside Act 1981, which makes it an offence to plant or otherwise cause the species to grow or spread in the wild. Landowners and developers are responsible for preventing established plants from spreading to neighbouring land.

Several other pieces of legislation are also relevant. The Anti-Social Behaviour, Crime and Policing Act 2014 can be used where the presence of giant hogweed causes a community protection issue.

The Control of Pesticides Regulations 1986 govern the use of herbicides in managing the plant. The Invasive Alien Species (Enforcement and Permitting) Order 2019 implements additional controls on invasive non-native species at a domestic level, in line with wider international obligations.

The Environmental Protection Act 1990 classifies removed plant material as controlled waste, meaning it must be disposed of lawfully.

Do You Have to Report Giant Hogweed?

There is no legal requirement in the UK to report sightings of giant hogweed. It is, however, illegal to take any action that causes this invasive plant to spread in the wild. Voluntary reporting is worth considering in certain circumstances, for example, if the plant has appeared for the first time in a particular location, if it is found within or near a protected or conservation site, or if there is a risk of spread into sensitive habitats. Both local authorities and relevant environmental agencies accept reports on invasive non-native plant species. 

Giant Hogweed Survey

A giant hogweed survey is a ground-level ecological assessment carried out to establish whether this invasive non-native plant is present on a site, determine the extent of any infestation and identify the most appropriate approach to controlling and removing it.

The survey is conducted by a qualified ecological consultant and results in a written report setting out the findings and a recommended management strategy.

If giant hogweed is found or suspected on your development site, arranging a professional invasive species survey is the most effective way to protect your planning application from delays and demonstrate to your local planning authority that the issue is being properly managed.

When is a Giant Hogweed Survey Carried Out?

The giant hogweed plant follows a seasonal growth cycle. Flower heads become clearly visible between May and June and the plant reaches its maximum height between July and August before beginning to die back in autumn. Survey season runs from May to September, when this invasive plant is at its most visible and identifiable. Working within this window allows the ecologist to confirm the extent of the infestation and begin control work before the plant sets seed, reducing the risk of further spread.

If your project timeline means a survey cannot be completed within the survey season, discuss this with your ecological consultant at the earliest opportunity so that a suitable programme can be planned.

What Does a Giant Hogweed Survey Involve?

A giant hogweed survey typically involves the following stages. 

Initial Site Assessment

A qualified ecologist carries out a systematic walkover of the entire site, including any water features and their margins, recording the location, density and extent of any giant hogweed present.

Other invasive or notable plant species will also be noted if encountered during the assessment.

Mapping and Risk Analysis

The distribution of any infestation will be mapped and the risk it poses to the development and to neighbouring land assessed.

The ecologist will consider whether the plant’s presence is likely to affect the planning process and identify areas where control work is most urgently needed.

Management Plan

If the ecologist has found giant hogweed, a tailored management plan will be drawn up to control giant hogweed.

Control methods may include herbicide application, manual removal of tap roots to remove an entire plant or a combination of both, depending on the scale and location of the infestation. Guidance on safe handling and disposal of removed material will also be provided.

Monitoring and Reporting

A written survey report will be produced, setting out the findings, the management recommendations and any follow-up actions required.

Ongoing monitoring visits may be recommended to confirm that control measures are working effectively, particularly for larger or more established infestations. Reports will satisfy a local council or environmental authority that the correct steps are being taken to manage this invasive plant.

Giant Hogweed and Other Invasive Species

Giant hogweed surveys are sometimes carried out alongside assessments for other invasive non-native species such as Japanese knotweed and Himalayan balsam, or in conjunction with injurious weeds surveys covering native plants controlled under the Weeds Act 1959.

If your site may be affected by more than one type of invasive vegetation, it is worth discussing a coordinated survey programme with your ecological consultant to keep the process as efficient as possible.

Book Your Giant Hogweed Survey

Identifying and instructing an experienced ecological consultancy early in the development process is the most effective way to avoid disruption to your programme.

An ecologist with local knowledge and experience of invasive species management will be best placed to advise on how to control giant hogweed and the full scope of work your site may require.

Use our free service to get fast, no-obligation quotes from trusted providers in our network. Fill in the form at the top of this page, and we will connect you with a specialist who can assess your site and help your project move forward.