Darren Greatbatch, Specialist Advisory Manager, Amenity & Invasive Weeds, at Environment Controls.
Last reviewed on .
How to identify Giant hogweed
On this page we show you the key characteristics of this invasive plant and what it looks like through the seasons.
What is Giant hogweed?
Giant hogweed (Heracleum\ mantegazzianum) is a highly invasive plant (part of the carrot family) that grows to impressive heights. The plant is identified by its tall, purple-blotched, bristly stems, large, jagged leaves, and huge umbrella-shaped clusters of white flowers.
Giant hogweed is a biennial or perennial herbaceous plant that can grow up to 5 metres in height. Flowering does not occur until the second or third year, or longer if conditions are unfavourable, but when it does, the white flowers look like very large cow parsley, with a pale, swollen rootstock. It produces 20-50,000 viable seeds a year, which are penny sized and paper thin and germinate quickly.
Giant Hogweed is a highly toxic plant that causes severe skin burns and scarring. Its sap can react to sunlight and lead to long-term injuries – especially dangerous on sites with public access, residential gardens, or active construction zones.
Under the Wildlife and Countryside Act 1981, landowners must prevent its spread. That means if it’s on your land – it’s your legal problem to solve.
What does Giant hogweed look like?
Giant hogweed can be identified by a number of key characteristics:
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- Hollow stems
- Hairs on the stems
- Stems grow to 5-10 cm diameter
- Stems have purple speckling on
- Large spiky leaves up to 1 metre across (as seen in the picture below)
- Flower umbrells can be 80 cm across and grow from a central stem
- Flower heads first appear as a closed pod which unfurls to reveal clusters of small cream-white flowers
- Seeds are small, paper like texture with dark stripes
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At the top of its long stems sit several heads of flower clusters. Individual clusters grows from stalks that form from the centre of the head at the top of the stem.
Looking up from the ground we can clearly see the umbrella shape flower (seed) heads that form at the top of the tall stems.
Giant hogweed’s growth lifecycle
In spring Giant hogweed plants emerges with large leaves that grow horizontal to the ground.
They quickly form dense mats across forest floors but equally thrive in urban settings.
The flower heads start as cone like structures at the top of each stem – which gradually unfurl to reveal the leaves and flower pods.
As the plant progresses it’s easy to see the hairs on its stalks and the clusters of tightly packed flower pods. Later these pods will form the flower heads.
As the plant reaches full height and full bloom its impressive height and structure can clearly be seen as it blanket covers large swathes of ground.
This image above shows winter canes with the dead flower heads that are now seed heads (shown below) that are brown and brittle. Seed disperse from the seed heads and can be carried many metres afar.
Need help with Giant hogweed?
We’re experts in identifying, treating and removing Giant hogweed, get in touch to speak to the team.