Giant Hogweed Identification20th July 2015
Don’t be scared, be informed! 🙂 The tabloids have been having a field day with Giant hogweed over the last few weeks, and due to the danger it poses; for once I think they aren’t far from the mark.
A little knowledge and some respect for the plant should keep you and your loved ones safe. So here’s what we know about it.
Giant Hogweed is a notoriously dangerous plant which though uncommon in the UK is something you are likely to see if you spend a lot of time walking beside rivers and streams. That is its habitat; you will rarely find it far from a fresh water source.
The danger with Giant Hogweed is not poisoning, but in the way that its sap reacts with your skin. If you get the sap on you then it will react with the melanin in your skin, and removes any protection that patch has from UV light.
If the hairs or sap come into contact with your eyes they can cause blindness!
The furocumarins that cause this effect are present in all parts of the plant.
This means that if you get it on your skin and your skin in the sun you will burn severely. The sap does not stop there though; it actually genetically alters that patch of skin so that all skin produced there for up to 7 years will have little protection from the sun.
Many plants including parsnips and common hogweed contain phototoxic sap, but none in the UK are anywhere near as severe as that of giant hogweed, though on sunny days we recommend harvesting common hogweed or even parsnips with gloves on.
With Giant Hogweed you don’t have to break the plant and rub the sap on you for the effect to take place either. The stems have fine needle like hairs that will cause irritation simply by touching it. So the rule is just stay away from the plant if you see it.
DEFRA are trying to eradicate the plant from the UK as it is a non native species. It was first introduced by the Victorians due to its majestic size, huge flowers and pre-historic looking leaves. It originated in the Caucasus Mountains in Southern Russia and around Georgia.
Giant Hogweed is mainly a danger for children who may well use the long stems to play with as swords, pea shooters or telescopes. Walkers who may brush against it, or gardeners who may unwittingly strim the plant getting the sap on themselves.
Giant hogweed can grow to more than 4 metres tall, with flower umbels that can reach 2 feet in diameter. The numerous flower umbels on each flower stalk can measure metres in diameter altogether.
|Size is one of your key identifiers here.
As shown in the photo above Giant
Hogweed will grow to 4 metres tall or
more before flowering.
|Common Hogweed will normally grow to
roughly 2 metres tall, I have seen it grow to
3 metres beside fresh water sources.
There are other key differences too.
Common hogweed seems to prefer roadsides to riversides, but it will grow almost anywhere. Giant Hogweed is almost exclusively a riverside plant.
|Giant Hogweed will have 50 or
more flower stems on each flower
|The number of stems on each flower of
common hogweed will normally not get to
more than 21.
|The main stem of giant hogweed
is reasonably smooth in
comparison to common hogweed,
except at the leaf joints which are
markedly more hairy than the rest
of the stem.The stem can also reach 5 inches
The main stem of giant hogweed
|Common Hogweed stems rarely
reach more than a couple of
inches in diameter.They are generally hairy all over, and
though some will show purple colouring
most remain green.
Look for last years stems to help you
|The leaves of Giant Hogweed are larger, shinier, more sharply serrated and more importantly, hairless.
They normally have a more serrated
|The leaves of Common Hogweed,
are generally smaller, softer, more
rounded and less shiny due to many
small hairs, but you will find examples
with very serrated leaves too.
Safe identification of Common Hogweed is essential, but once you know both plants mistakes are hard to make.
Caution when harvesting hogweed, e.g. protecting your skin and wearing gloves is still recommended though.
Common Hogweed really is one of our favourite edibles so we highly recommend you try it, and we hope this article and videos keep you safe when you do :).
More details on both plants can be found in our Hedgerow Food Guide.
Giant Hogweed, Heracleum mantegazzianum
Common Hogweed, Heracleum sphondylium
Hi again, I’ve read that giant hogweed stems don’t have grooves in them! Is this true? That would be an easy clincher for me.
Hi Steve, this is not true I’m afraid. the safest thing to go by is that common hogweed has suede like hairs on the upper surface of the leaves, giant hogweed does not have these hairs and has shiny leaves.
How do we tell the difference between giant hogweed and angellica. Every description I’ve found is pretty much the same and no article mentions both? Thanks
Angelica had separate leaflets, giant hogweed leaves are all part of a vicious looking, serrated leaf running most of the length of the leaf stalk. Size is the most obvious difference and by now giant hogweed would be two plus meters tall, angelica won’t generally get larger than 1.5 meters in it’s life. Giant hogweed has 50 to 150 separate ‘spokes’ per flower head, angelica has at most 30. Giant hogweed has hairs all over the stem and underneath the leaves, angelica is fairly hairless.
Are dried giant hogweed still dangerous, i.e. the ones in seed? And how do you identify them?
Giant hogweed ‘skeletons’ will still be very tall, have a thick stem and will have many more seeds than common hogweed.
Hi have a giant hog weed in my garden, at first I though it was a pretty fern, suddenly it was my height 5ft , I hope I’ve destroyed them as their were two one still small I put rubber gloves on at dusk cut it down straight into black bin bag poured weed killer to kill roots and covered it to stop light getting to it . I have two elderly dogs I need to protect them as I’m elderly flower were just ready to open , have I done the right thing
It sounds like you have been very thorough, it may come back later in the year or next Spring but if you dispose of it, it should be no problem to your dogs. It might be Common hogweed, it grows to about 1.5 to just over 2 meters, giant hogweed will have a stem the size of a wine bottle, leaves as long as your arm and flowers the size of a dustbin lid. The upper surface of common hogweed leaves has a fine coating of suede like hairs, you may need to look at it from different angles to observe them, giant hogweed has a shiny, hairless upper surface to the leaves.
Be aware of the rare occurrence of hybrids between giant hogweed and common hogweed where both parent plants are present.