Darren Greatbatch, Specialist Advisory Manager, Amenity & Invasive Weeds, at Environment Controls.
Last reviewed on .
Introduction
Here we explain how to identify Giant hogweed in autumn, and show you the easy signs Giant hogweed is dying back to watch out for that.
In autumn, Giant hogweed stands out by its tall, dead, hollow stems and the remains of its large flower heads, which often linger as umbrella-shaped seed clusters. The lush green leaves of summer have withered, leaving grey, dead foliage at the base. Under the right conditions, both stems and seed heads remain visible long after the growing season ends.
Key Features in Autumn
- Tall, dead stems: Hollow and often several metres high, unless they have been knocked down by passing wildlife these are the most noticeable signs of the plant after summer moves into autumn.
- Seed heads: The large, umbrella-shaped flower clusters dry and form large seed heads that can remain intact well into autumn.
- Dead leaves: Large, jagged leaves die back and collapse, often leaving a rosette of shrivelled, grey leaf remains at the base of the plant.
- Seeds on the ground: A single plant produces tens of thousands of seeds, which can accumulate in dense layers, especially in sheltered areas.
Similar Species
Common hogweed (Heracleum sphondylium) above
- Grows up to 2 metres tall (much smaller than giant hogweed).
- Stems lack purple blotches and are hairier and softer.
- Leaves are rounder, less jagged, and not as deeply divided.
Cow parsnip (Heracleum maximum)
- Typically reaches about 2.5 metres in height, so much shorter than giant hogweed.
- Stems are green, ridged, and hairy, without purple blotches.
- Leaves have rounded lobes. Its sap can still irritate skin if exposed to sunlight.
Poison hemlock (Conium maculatum)
- Much smaller than giant hogweed but has purplish stem blotches.
- Smooth, hairless stems with fine, fern-like leaves.
- Extremely toxic—any contact or ingestion is dangerous and potentially fatal.
Guidance for Property Managers and Landowners
Recognising Giant hogweed at this stage of growth is essential, as unmanaged plants can still spread through thousands of viable seeds, creating a long-term liability on your land.
Why This Matters
- Legal duty: Under the Wildlife and Countryside Act 1981, it is an offence to cause giant hogweed to spread into the wild.
- Health and safety: The sap remains hazardous. Dead stems and seeds still pose risks for contractors, site users, and residents.
- Long-term liabilities: Untreated seed spread can create ongoing infestations, impacting property value and compliance obligations.
Property managers and landowners should ensure professional identification and management, even outside the growing season, to control spread and remain compliant with legislation.
Treatment and Removal
Due to the health risk that this plant poses we advise contacting us to get advice and a quote for treatment or removal. We can offer a range of options from a herbicide programme to digging it up. More information here.