How to identify giant hogweed — and the four plants that fool everyone
The visual checks that separate Heracleum mantegazzianum from cow parsley, hogweed, hemlock and angelica — and what to do if you've touched it.
Giant hogweed is the only invasive on our books that is genuinely dangerous to touch. Misidentifying it works in both directions — people panic over harmless cow parsley, and walk straight through patches of the real thing on the way to school.
The four reliable tells
- Height: a mature plant is 2–5 m. Native umbellifers rarely exceed 2 m and almost never exceed 1.5 m.
- Stem: thick (4–10 cm diameter) with prominent purple blotches and stiff white bristles.
- Leaves: deeply lobed and jagged, up to 1.5 m wide. Nothing native comes close to this size.
- Flowers: huge white umbrella heads up to 60 cm across, June–August.
The look-alikes
- Common hogweed (Heracleum sphondylium) — same flower shape but knee- to chest-height, plain green stem, leaves under 60 cm.
- Cow parsley (Anthriscus sylvestris) — early summer, lacy foliage, hollow grooved stem, peaks 1–1.5 m.
- Hemlock (Conium maculatum) — purple-blotched stem like giant hogweed but lacy ferny leaves and a foul mousy smell when crushed. Toxic if eaten but does not burn on contact.
- Wild angelica (Angelica sylvestris) — pinkish umbel, smooth stem, harmless.
If you've touched it
Wash the affected area immediately with soap and cold water. Cover it from sunlight for at least 48 hours — the photo-activation by UV is what causes the blistering, not the sap itself. Seek GP or A&E advice if blistering develops.
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The survey team
PCA-certificated surveyors, Japanese Knotweed Elimination
PA1 / PA6A certificated surveyors who carry out the site visits, write the management plans and sign off the reports issued to lenders and solicitors.
Reviews the technical, legal and lender statements in this article.
What this page can't tell you
- Guidance is general. Identification, treatment choice and timescales can only be confirmed by a site visit — photographs alone are indicative.
- Lender and insurer requirements vary by institution and change over time. We state what is typically accepted, not what any named lender will accept on your case.
- Guarantee (IBG) eligibility depends on the plan chosen, the survey findings and the underwriter's acceptance. It is not automatic.
- Legal points summarise published law and guidance current at the review date. They are not legal advice.
Last reviewed · Questions on anything stated here: 07582 869979
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