The Giant Hogweed-Heracleum mantegazzianum

Photograph courtesy of GerardM at nl.wikipedia

Heracleum mantegazzianum

The giant hogweed belongs to the Apiales order of flowering plants and placed in the Family Apiaceae formerly called the Umbelliferae and given the genus name of Heracleum. The genus name refers to Hercules of Greek mytholgy who was said to have used members of this genus as medicinal herbs.

The species is a native of the Causacus region and central Asia and was introduced in to this country in 1893 by the Victorians as an ornamental garden plant.  Like so many introductions the plant escaped over the garden wall into the wider countryside and is now established. It is considered to be an invasive alien and has been labeled as a "Hazardous species"

Giant hogweed is named in the Wildlife and Countryside Act 1981 {as amended} which provides the primary controls on the release of non-native species into the wild inGreat Britain. It is an offence under Section 14{2} of the Act to "Plant or otherwise cause to grow in the wild " any plant listed in Schedule 9 part 11, this includes Giant hogweed.


The stems, edges and undersides of the leaves are adorned with hairs containing a poisonous sap, and the slightest touch can cause painful blistering and severe skin irritation. Unshaded habitats with high soil nitrate levels tend to produce the greater quanities of toxin in the plant.

Contact with the cut material in sunlight produces skin reaction in almost all cases, blistering symptoms occur 24-28 hours after exposure, and dense pigmentation is visible after 3-5 days. This may persist for 6 years or more. Protective clothing must be worn when cutting or strimming hogweed  [see Common Hogweed} and especially so the giant hogweed.  


New young foliage of giant hogweed    Photo by Dal

The root is a deep taproot. The stem, which is capable of reaching the height of to 14 feet or more, is thick, ridged and greenish purple in colour, sometimes green with purple blotches, always covered in sturdy white hairs.

The foliage which forms a large rosette in late April oe early May have broad blades that have a jagged appearance and spiky at the ends are much divided into broad lobes. The lower leaves including their stalks can attain the length of 1.5 metres. They have at the rosette stage  a superficial resemblance to wild rhubarb leaves.

The flowerheads consist of large umbels of white flowers which are unmistakeable for the heads are larger than dinner plates. They may be borne some 14 feet above the ground and make an impressive sight, it is easy to see why the Victorians wanted this awesome plant in thier gardens. There are several hundred individual white flowers per head. They flower in June and July.

The flowers are succeeded by flattened seed fruits approximately 10mm x 7mm. The palnt is capable of producing 50,000 + seeds per season. They are designed by nature to float , thus they are rapidly dispersed along water courses., they are also dispersed by wind, water and of course man. Studies have revealed that the seeds remain viable for up to 15 years.

Flower heads of the Giant hogweed are impressive.

Photograph courtesy of Farbenfreude creative commons attribution


It was not until the late 1950s and during the 1960s when children began turning up at A&E departments at local hospitals with severe blistering around their mouths, that it became apparent, how dangerous this palnt can be.

In the days before computers and other electronic gadgets, children would use the hollow stems for pea-shooters and blow pipes. The toxic sap quickly caused the blistering to occur.

The Environment Agency gives this advise to anyone trying to eradicate this plant and for those who work for the Countryside ranger services or utility workers---

" Chemical control is the most effective; spraying can start as soon as the plant is about 1 metre high, usually in March or April and continue to spray throughout the summer. More than one application is often necessary and follow up spraying will be required to kill seedlings in subsequent years."


" Cutting down stems with a sharp scythe before flowering will help to control this plant. Flail mowing is possible with extreme care due to the risk of being sprayed with sap. Protective clothing must be worn  {including goggles or other eye protection} The crown may be dug out just below the ground which prevents regrowth, provides good control.

Grazing by cows and sheep will suppress growth but will not eradicate it.  

it is essential to establish vegetation quickly after control measures have been applied, as dense grass swards tend to discourage seed germination" Disposal should be taken to a landfill site or be piled on site for composting"


  DID YOU KNOW-THAT--Sometimes hybrids occur between The giant hogweed and the common hogweed Heracleum sphodylium. 

That--It takes the giant hogweed 4 years to flower,after which it dies.

Whilst attaining the age of four years the plant dies back in winter and starts to regrow again in March and April.

A single plant can soon produce a small colony.

Giant hogweed is attacked by a number of insect species but none to sufficient damage to be useful.

Fungi such as powdery mildew and various soft rots affect the plant but again not enough to cause severe damage.

Snails graze the plant. 



Associated pages-Click on the content banners at the top of this page.

Common Hogweed.



Fools parsley.

Cow parsley.

Poisonous plants-3 {Hemlock water dropwort}. 

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Poisonous plants-2 Hemlock.

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