What is giant hogweed?
All you need to know about identifying and controlling giant hogweed.
What is giant hogweed?
Giant hogweed (Heracleum mantegazzianum) is a non-native, invasive weed. Native to southern Russia, it's a member of the Apiaceae family and is closely related to cow parsley, carrots and parsnips. Originally introduced to the UK as an ornamental plant in the 19th century, it has large, umbrella-shaped flower heads and can grow to over 3m (10ft) in height. However, its sap can cause severe burns if it comes into contact with human skin.
Giant hogweed can now be found throughout much of the UK, especially waste ground, roadside verges and river banks, where its seeds are transported by water. It grows in dense clumps and can out-compete native plants.
It's listed on Schedule 9 of the Wildlife and Countryside Act in England and Wales, and the Government's list of Invasive Non-Native Plant Species of special concern. While it's not an offence to have giant hogweed already growing in your garden, it is an offence to plant or otherwise cause to grow it in the wild. It is also banned from sale in the UK. You should stop giant hogweed spreading from your garden and avoid accepting gifts of these species.
Is giant hogweed dangerous?
Yes. Giant hogweed has phototoxic sap, which makes skin extremely sensitive to sunlight. If giant hogweed sap gets onto your skin and the skin is then exposed to sunlight, it can burn and blister. These blisters may last for several weeks and may even recur over months or even years.
If you touch giant hogweed and do get its sap on your skin, wash your skin immediately, taking care to ensure all sap has been rinsed off. Then keep the area covered for the next few days, to avoid it being exposed to sunlight. You may want to seek medical advice.
It's important to also keep dogs away from giant hogweed, as they are also affected by its sap.
What does giant hogweed look like?
Giant hogweed looks like a much larger version of cow parsley. Biennial, it forms a rosette of lobed leaves in its first year before sending up a flower spike in its second year, and then setting seed and dying.
- Stems are hollow and ridged, green with purple blotches and stiff, white hairs
- Leaves are up to 1.5m wide and 3m long, and are deeply divided, with many fine hairs on the underside. They slightly resemble rhubarb leaves, but have more jagged edges
- Flowers are small, white or tinged with pink, and are borne in upward-facing clusters, known as umbels, in early summer. Umbels can reach a diameter of 60cm
- Seeds are 1cm long, striped, flattened and oval
How to tell giant hogweed apart from similar plants
Giant hogweed looks similar to, and therefore may be confused with, the following plants:
Common hogweed (Heracleum sphondylium) – growing to just 2m, this British native hogweed is much smaller than giant hogweed, and has more rounded, and less jagged leaves. It's not toxic and is a fantastic wildlife plant.
Cow parsley (Anthriscus sylvestris) – cow parsley has a more delicate appearance than giant hogweed, with feathery, almost lacy leaves, and smaller flower heads. It grows to a maximum height of 170cm.
How to get rid of giant hogweed
Chemical – weedkillers such as glyphosate may be used to get rid of giant hogweed but bear in mind that they could harm other plants growing nearby and could leach into the soil and waterways. What's more, you will still need to wear full protective clothing, dispose of the plants and then continue making applications as any seeds germinate.
Natural – this is the best way to remove giant hogweed. Giant hogweed is biennial, so forms a basal clump of leaves in its first year and then flowers and sets seed in its second year. Removing it by hand requires full protective clothing, to stop any sap from being in contact with the skin. To remove it successfully, dig out the whole plant, ideally in its first year, before it flowers and sets seed. Bear in mind that seeds can survive for several years, so you may need to remove seedlings in future years.
How to dispose of giant hogweed
Giant hogweed can be disposed of in landfill sites but only those with licences to deal with 'controlled waste'. Instead, burn or compost giant hogweed in your garden. If composting, keep the seeds to one side and burn them anyway, as they may survive the composting process.
Frequently asked questions
Should I report giant hogweed in the UK?
Yes, if you find giant hogweed growing on council-owned land, report it to the council – their website will often have a page dedicated to reporting invasive, non-native species. If you find giant hogweed growing on a railway line, embankment, or station, report it to Network Rail.
Is giant hogweed poisonous for dogs?
Yes, giant hogweed is very poisonous to dogs, and can cause severe skin burns and abrasions, mouth ulcers and even vomiting and diarrhoea.
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