The Weed of Hercules

Giant Hogweed (Heracleum mantegazzianum)

Giant Hogweed (Heracleum mantegazzianum)

Dear Readers, during my trip to the Olympic Park a few weeks ago I was astonished to notice an eight-foot tall Giant Hogweed standing on the bank of the canal next to the Aquatic Centre. I saw ‘astonished’ because the area does not want for gardeners, and also because this is not a shy demure plant of the kind that I usually write about. No, this plant is a pirate, with flower heads the size of dinner plates and a potential height of up to 18 feet tall. It is also not something that you want to have around if you have children, or anyone vulnerable, for this is that unusual thing: a plant that lives up to the hype.

Those of you old enough to remember the 1980’s might remember a programme featuring, I think, Esther Rantzen, in which the full horror of Giant Hogweed was revealed. The plant’s  sap contains chemicals  called furocoumarins, which are released when the plant is damaged, whether through strimming when the plant is young, or through being macheted down when mature. Children are particularly attracted to the plant because of its extraordinary size – it makes even an adult feel as if they are in Land of the Giants – and the hollow stems invited use as a blowpipe. Unfortunately, the sap, whilst initially appearing to cause no problems, actually changes the structure of the skin if it touches it. If that skin is exposed to sunlight, the result can be as minor as a rash, or as extreme as severe, lymph-filled blisters that may require hospitalisation. Furthermore, the skin will erupt again whenever exposed to sunlight.  Although there have been many ‘scare stories’ in the media about perfectly innocent plants, for this one it seems that many of the claims are justified. For a full and detailed picture of what’s been happening with the plant, I recommend our old friend The Poison Garden  website, where all things Hogweed-ish are discussed. There is also an excellent section on this website about identification of Giant Hogweed, and how to tell the difference between it and the Common Hogweed (Heracleum spondylium). Incidentally, Common Hogweed (which is very common as its name might suggest) also contains furocoumarins, but seemingly at a much lower concentration than its giant relative. I would also suggest protective measures if you are strimming a patch of this plant.

Incidentally the band Genesis, who were responsible for introducing both Peter Gabriel and Phil Collins to an unsuspecting public, included a song about Giant Hogweed on their Nursery Crymes album. For your delectation, here is a live rendition from 1973. You’re welcome.

Des Colhoun [CC BY-SA 2.0 (], via Wikimedia Commons

Giant Hogweed flowers (Photo One – see credit below)

The Latin name ‘Heracleum mantegazzianum’ refers firstly to Hercules (probably because of the plant’s outrageous size) and then to Paolo Mantegazza, a nineteenth-century anthropologist who may have been the first person to extract cocaine from the coca plant. The plant is originally from the Caucasus, and was introduced to the UK by the Victorians, who were rather taken with how pretty it was, and what a fine show it made alongside the lakes and rivers of their estates. Alas, as is often the case, the plant did not stay where it was put, which will be of no surprise to the readers of this blog. It can now be found in North America, New Zealand and most of Europe. Although the seeds are rather heavy (as you might expect of something this size) and fall close to the parent, they can be easily transported on the soles of the shoes of the unwary, and I wonder if they can also survive falling into water and being carried that way. Certainly I have no idea how on earth the Olympic Park specimen turned up.

© Copyright Gordon Brown and licensed for reuse under this Creative Commons Licence

A Giant Hogweed bud. Don’t get too close now….! (Photo Two – credit below)

Getting rid of Giant Hogweed is an expensive and difficult business. Nothing short of full-body cover and protective glasses will do. Seeds are viable for up to seven years, and so annual spraying in the spring (with all its concomitant health and environmental hazards) needs to be take place. As John Robertson explains in The Poison Garden, the only alternative to spraying is to completely replace the topsoil, which can cost many thousands of pounds that councils currently don’t have.

By Huhu Uet (Own work) [GFDL ( or CC BY 3.0 (], via Wikimedia Commons

The magnificent Giant Hogweed (Photo Three – credit below)

I had a momentary dilemma about what to do about the Giant Hogweed. It is a truly magnificent plant, and in its native lands it probably goes about its business unmolested, as presumably local people know what it is, and how to deal with it. But here, in London, next to the most popular swimming pool in the capital? I sent the Olympic Park team an email telling them I’d spotted Giant Hogweed, and they emailed back to say that they will remove it. Do I feel as if I betrayed a true wonder of the natural world? Yes. But people, especially children, will be curious about the plant, and will not know about the danger that it represents. For once this particular Giant Hogweed really does meet the definition of a ‘weed’ – the wrong plant in the wrong place at the wrong time.

 © Copyright Roger Kidd and licensed for reuse under this Creative Commons Licence

Photo Four (credit below)

Photo Credits

Photo One – Des Colhoun [CC BY-SA 2.0 (], via Wikimedia Commons

Photo Two – © Copyright Gordon Brown and licensed for reuse under this Creative Commons Licence

Photo Three – By Huhu Uet (Own work) [GFDL ( or CC BY 3.0 (], via Wikimedia Commons

Photo Four – © Copyright Roger Kidd and licensed for reuse under this Creative Commons Licence

5 thoughts on “The Weed of Hercules

  1. Ann

    You did the right thing, I’m sure: far better for the park people to deal with one specimen than with hundreds. Do pollinators like it, by the way?

  2. Lynn D.

    Giant hog weed appeared on my creek bank for the first time this year. I carefully removed it before it went to seed and sent it in a plastic bag in the dust bin to go to the garbage burning plant. Some weeks later I was taking a walk along the creek some miles upstream and found many plants growing on property owned by the state of Oregon, so my plant probably came from seeds upstream. I can’t believe how many plants we have in common even though we are continents apart!

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