Updated August, 2021
What is Giant Hogweed?
Giant hogweed (Heracleum mantegazzianum) is a plant in the same family as parsley, carrot, parsnip, cumin and coriander. Its growth pattern is similar but it is definitely not edible and can cause serious injury if you come into contact with it.
Giant hogweed is found across the UK, it is not dissimilar in appearance to Cow Parsley (Anthriscus sylvestris). The way I usually describe Giant Hogweed however is “Cow Parsley on steroids!” The small umbrella like stalks of Cow Parsley are very thick and bulging and flowers in May-June, grows up to 1.5m high and is one of the earliest flowering umbellifers. It is also one of the most common roadside and hedgerow plants. It smells strongly of aniseed if you crush the leaves – don’t do this unless you’re sure what you’re looking at though!
What does Giant Hogweed look like? – a useful ID guide from the Woodland Trust:
Giant Hogweed, when fully grown, can reach heights between 1.5m to 5m and have a ground spread between 1 and 2m so it definitely lives up to its name. It forms a rosette of large jagged, lobed leaves in the first year before sending up a flower spike in the second year and then setting seed.
Stems are green with purple blotches and stiff, white hairs. Stems are hollow with ridges and have a thick circle of hairs at base of each leaf stalk.
Leaves are huge,and can be between 1.5m wide and 3m long and is deeply divided into smaller leaflets and is hairy underneath. It looks a bit like a rhubarb leaf, with irregular and very sharp or jagged edges.
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.
Why is Giant Hogweed dangerous?
The dangerous part of Giant Hogweed is its sap which can come from its leaves, stem or flower head structures. The sap is clear and watery and can get onto your skin through touching any part of the plant.
The sap is phototoxic meaning it reacts to light. Contact with the plant sap prevents the skin from being able to protect itself from sunlight, which leads to phytophotodermatitis, a serious skin inflammation. A reaction can begin as soon as 15 minutes after contact with the sap. Sensitivity to light peaks between 30 minutes and two hours after contact but can last for several days.
On a summers day, this can lead to burning, inflammation and blisters can be very severe, and lead to scarring. The scarring can last for months and will return when you go out into the sun again.
Any contact with the eyes can be very damaging, and potentially lead to blindness in some cases.
In short, the plant causes a chemical burn on any part of your body that comes into contact with it.
First Aid for Giant Hogweed burns:
Prevention is best so don’t touch it! Educate your children to stay away as well.
If you do come into contact with Giant Hogweed:
- Immediately wash the area with copious soap and cool water
- Don’t burst any blisters – seek medical help if they are extensive
- Stay out of any sunlight for at least 48 hours
- Monitor for any delayed reaction.
- Flushing the eyes with copious fresh water as a precautionary measure is also advisable.
- Thoroughly and quickly wash the clothes you were wearing when you came into contact with the plant.
It is worth noting that for some people, Cow Parsley can also be an irritant, although typically with much milder effects.
As always, if in doubt, contact a medical professional and tell them the situation. See your local pharmacist, GP or go to A&E if symptoms are blistering, painful or not improving.
Giant Hogweed is also a ‘notifiable plant’ that should be reported.
Giant hogweed should be reported to your local council. This is best done through their website as you then get a reply from the correct department. Make a note of the exact location of the plants using a grid reference or What3Words.
It is an offence to allow non-native plants to spread into the wild , e.g. by allowing it spread from your land through inactivity or releasing seeds, by dumping garden waste into the wild, by moving contaminated soil etc.
You can find out more about non-native species and action to report and remove them on the Scottish Invasive Species Initiative website.