Giant Hogweed Isn’t Like Other Weeds. It Can Seriously Hurt You.
The sap causes severe burns and permanent scarring when exposed to sunlight. Before you tackle it, you need the right protection – and for larger infestations, professional help may be the safest option. For young plants you can treat safely yourself, a systemic weedkiller reaches the roots without you having to dig.
Most common UK weeds are just annoying. Giant hogweed is genuinely dangerous.
Its sap contains chemicals called furanocoumarins that react with sunlight to cause severe burns, blistering, and permanent scarring. Get the sap in your eyes and you risk blindness. This isn’t exaggeration – it’s why giant hogweed has been called Britain’s most dangerous plant.
It’s one of several plants in the UK that pose genuine health risks, alongside ragwort (toxic to livestock) and Himalayan balsam (invasive species) – though hogweed’s danger to humans is far more immediate.
If you’ve found giant hogweed in your garden, don’t panic – but do take it seriously. This article will help you identify what you’re dealing with, protect yourself properly, and remove it safely.
Giant Hogweed vs Common Hogweed
First, make sure you’re actually dealing with giant hogweed. There’s a native species called common hogweed that looks similar but is much less dangerous.
Giant hogweed (Heracleum mantegazzianum):
– Grows up to 5 metres tall (that’s over 16 feet)
– Thick stems with distinctive purple-red blotches and coarse bristles
– Flower heads up to 60cm across
– Leaves can reach 1.5 metres wide with jagged, pointed lobes
– Highly toxic sap – causes severe photodermatitis
Common hogweed (Heracleum sphondylium):
– Grows up to 2 metres tall
– Green stems without purple blotching
– Smaller flower heads, around 20cm across
– Leaves more rounded, less jagged
– Can still cause mild skin irritation, but far less severe
The purple blotches on the stem are the key identifier. If you see a cow-parsley-type plant with thick, bristly stems covered in purple-red markings, treat it as giant hogweed until proven otherwise.
Why Giant Hogweed Is Dangerous
Giant hogweed sap contains furanocoumarins – chemicals that make your skin extremely sensitive to UV light. You won’t feel anything at the time of contact. But when the affected skin is exposed to sunlight (even through clouds), the reaction begins.
Within 24-48 hours, you’ll experience:
– Severe redness and inflammation
– Large, painful blisters
– Burns that can take months to heal
– Permanent scarring and skin discolouration that can last years
If sap gets in your eyes, it can cause temporary or permanent blindness.
Children are particularly vulnerable – the hollow stems look like perfect pea-shooters or telescopes, with horrific consequences.
Safety First: Protective Gear
Before you go anywhere near giant hogweed, you need proper protection. This isn’t optional.
Essential protective gear:
– Waterproof gloves that cover your wrists (not fabric gardening gloves)
– Safety glasses or goggles
– Face covering or mask
– Long sleeves and trousers in synthetic, water-resistant material
– Waterproof boots (not canvas shoes)
The sap can soak through cotton and other natural fabrics, so synthetic waterproof materials are essential. Cover all exposed skin.
After handling hogweed, wash all clothing immediately and separately from other laundry. Clean all tools thoroughly.
If you get sap on your skin:
1. Wash the area immediately with cold water and soap
2. Cover the affected skin to protect it from sunlight
3. Keep it covered for at least 48 hours
4. Seek medical advice, especially if blistering develops
How to Kill Giant Hogweed
Small Infestations (A Few Young Plants)
Young hogweed plants in their first year (before they send up flowering stems) are the easiest to deal with. They form rosettes of large, lobed leaves close to the ground.
For just a few young plants, you have two options:
Digging out: In full protective gear, use a sharp spade to dig out the root. You need to remove at least 15cm of the taproot to prevent regrowth. Do this in spring when the soil is moist and roots come out more easily. This is labour-intensive and means more contact with the plant – only recommended for very small infestations.
Weedkiller: A glyphosate-based systemic weedkiller is absorbed through the leaves and kills the entire plant including roots. This means less physical contact with the plant. Apply in spring when plants are actively growing (April-May) or to regrowth in late summer (August-September).
Larger Infestations or Mature Plants
If you have multiple mature plants, or plants that have flowered, seriously consider hiring a professional. This isn’t a failure – it’s common sense.
Mature giant hogweed plants are tall, difficult to handle, and produce up to 50,000 seeds each. One mistake can mean seeds spreading everywhere or sap contact causing serious injury. You may need the strongest weedkiller available for established plants.
Professional removal typically involves herbicide treatment over 2-3 years, with monitoring for regrowth from the seed bank.
What NOT to Do
Don’t strim or mow giant hogweed. This sprays sap everywhere, creating a serious hazard for anyone nearby.
Don’t tackle flowering plants yourself. A single flower head can carry thousands of seeds. If you’ve got flowering giant hogweed, contact your local council’s environmental team or hire professionals.
Don’t compost hogweed. It’s classified as controlled waste and must be disposed of properly (see below).
Disposal and Legal Requirements
Giant hogweed is listed under the Wildlife and Countryside Act 1981. It’s illegal to plant it or cause it to spread. If it’s already growing in your garden, that’s not an offence – but you must dispose of it properly.
Giant hogweed is classified as controlled waste. You cannot:
– Put it in your household bin
– Put it in council green waste
– Compost it at home
You must either:
– Burn it on your property (ensuring complete destruction)
– Take it to a licensed landfill site with proper documentation
– Arrange collection by a licensed waste carrier
If you’re unsure, contact your local council for guidance on disposal in your area.
Preventing Regrowth
Giant hogweed seeds can remain viable in soil for up to 15 years. Even after successful removal, you’ll need to monitor the area for several years and treat any seedlings that appear.
Check the site each spring and treat new growth promptly – young seedlings are much easier to deal with than established plants.
If your garden borders rivers, canals, or waste ground, be aware that seeds can blow or wash in from elsewhere. Regular monitoring is your best defence. The same vigilance applies if you’re also dealing with large weeds like brambles or Japanese knotweed that can harbour seedlings.
Frequently Asked Questions
What’s the difference between giant hogweed and common hogweed?
Size and stem markings. Giant hogweed grows up to 5 metres tall with thick stems covered in purple-red blotches and coarse bristles. Common hogweed reaches about 2 metres with plain green stems. Both are common in UK gardens, but giant hogweed is far more dangerous. When in doubt, treat any large hogweed-type plant with extreme caution.
What happens if you touch giant hogweed?
The sap makes your skin extremely sensitive to sunlight. Within 24-48 hours of sun exposure, you’ll develop severe burns, large blisters, and potentially permanent scarring. The reaction can continue for months, and skin may remain light-sensitive for years. If you get sap on your skin, wash immediately with cold water and keep the area covered from sunlight.
Do I have to remove hogweed from my garden?
There’s no legal requirement to remove it, but it’s strongly recommended for safety reasons. However, you are legally obliged to prevent it spreading, and if an environmental authority orders you to remove it, you must comply. Given the health risks, removal makes sense for any garden used by people or pets.
How do I dispose of hogweed?
Giant hogweed is controlled waste under UK law. You cannot put it in household bins, council green waste, or home compost. Either burn it completely on your property, take it to a licensed landfill with proper documentation, or arrange collection by a licensed waste carrier. Contact your local council if you’re unsure about disposal options in your area.
When is the best time to treat hogweed?
Spring (April-May) when plants are actively growing but before they flower. This gives the best herbicide uptake and prevents seed production. Treat any regrowth in late summer (August-September). Never attempt to tackle plants that are already flowering – the seed dispersal risk is too high.
The Bottom Line
Giant hogweed requires more respect than most garden weeds. Take the safety precautions seriously, know your limits, and don’t hesitate to call in professionals for larger infestations.
If it’s just a few young plants and you’ve got the right protection, you can handle this yourself. A systemic weedkiller means you don’t have to dig – and that means less contact with the plant.
