Giant hogweed warning sign to prevent anyone hurting themselves whilst it is being treated

There is a lot of confusion in identifying what the difference is between giant hogweed and Japanese knotweed in order to treat each one effectively within your garden.

In this article, we will look at both of these weeds, their similarities and what makes them different. We’ll also use photos to demonstrate how you can distinguish between the two as well.

It is well documented about the damage and legal issues that can be caused by Japanese Knotweed, but another in the knotweed is just as lethal. The giant knotweed and the giant hogweed.

It’s hard to say which plant is more invasive: the Giant Hogweed or Japanese Knotweed. Generally, it seems that in terms of sheer size and number of leaves per unit area, Hakonechloa macra (Giant hogweed) is a clear winner over Fallopia japonica (Japanese knotweed).

But while this perennial weed may not have as many leaves when compared with its Oriental counterpart, they are longer-lasting each year than Giant hogweed and if you see one on your property be sure to call for professional help immediately.

What is Giant Hogweed?

Giant Hogweed, like Knotweed, is an invasive plant that can grow to be over 10 feet tall. This plant is related to cow parsley, but unlike cow parsley, its sap can inflict severe burns when it comes into touch with human flesh.

While there is no legal requirement for a homeowner to remove Hogweed from their property, local governments will normally seek to have it removed if it is discovered in public spaces to prevent further harm. Giant Hogweed should be removed by a professional because it can cause serious burns if it is not removed properly.

Know the law

Giant hogweed (Heracleum mantegazzianum) is listed under Schedule 9 of the Wildlife and Countryside Act 1981 with respect to England and Wales. As such, it is an offence to plant or otherwise allow this species to grow in the wild.

How to identify it?

Similarly, to Japanese Knotweed, Giant Hogweed will noticeably change over the seasons. We have an infographic on how to identify Japanese Knotweed throughout the seasons here. If you’re looking for Giant Hogweed, you should generally try to identify:

  • Purple coloured thick, bristly stems
  • White flowers in clusters
  • A plant that looks much like cow parsley
  • Thick white hairs commonly found at the base of the plant
  • In winter, look for a woody stem and dead, grey looking plant
Giant hogweed and Japanese knotweed have similar looking flowers but differ in their shape and size
Giant hogweed and Japanese knotweed have similar looking flowers but differ in their shape and size

What is the difference between Giant Hogweed and Japanese Knotweed?

In the wild, it is possible to confuse Japanese Knotweed with Giant Hogweeds. However, they are two different plants and have very distinct differences that help them stand out from each other in a variety of environments.

For example, while their leaves may be similar looking on some occasions; if you were to look at both during early spring when there’s still snow or frost around- knots will emerge green as opposed to wilted by winter cold whereas hogweed would remain brownish or pale even up into late Spring/early Summer months due mostly because of its larger size (Japanese knotweed can grow well over 5 feet tall.)

Similarities:

  • It is illegal to plant or help to grow both Japanese Knotweed and Giant Hogweed in the UK.
  • Both of these invasive plants must be carefully removed and disposed of at a licensed landfill site. They can spread very easily and invade other areas.
  • Both of these invasive plants are injurious weeds as they cause a nuisance and/or harm to the area that they are in. Both of these also outgrow more favoured plants because of their height and strength.

Differences:

  • Whilst Japanese Knotweed can find homeowners in trouble for allowing it to grow on their properties, Giant Hogweed implies no obligation for the homeowners to remove it.
  • Japanese Knotweed can be cut down and eaten by humans and animals, as it has a rhubarb taste. Giant Hogweed on the other hand has a sap that will burn when in contact with sunlight and is toxic if eaten.
  • Japanese Knotweed causes harm to its environment by growing through roads, walls houses and spreading. Giant Hogweed on the other hand causes third-degree burns and blisters when its sap is exposed to sunlight and it touches your skin.

Removal of Giant Hogweed

It is recommended that this plant is controlled or eradicated, and you have a duty of care to prevent its spread from your property.

Often, Giant Hogweed can be treated without the use of chemicals to remove it. The plant can be dug out, but when this is not possible because of the size or depth of the plant, chemical control is a good option. Glyphosate-based weed killers work well with this invasive plant.

The plant may be hand-dug, but care must be taken to remove as much root material as possible, as a plant can grow from a section of root carrying auxiliary buds. Alternatively, the hogweed can be mechanically excavated, if allowance is made for the extensive seed bank.

Following excavation new seedling growth should be controlled by the use of the herbicide. Cutting of the plant is not an efficient long-term solution and is not recommended on any plant exceeding 1.5 metres in height due to the risk of direct contact.

Like Japanese Knotweed, Giant Hogweed must be disposed of as a controlled waste product. It must be taken off of the site to a licensed landfill.

Final thoughts

The differences between Giant Hogweed and Japanese knotweed are not only in the appearance of the plant but also in how to identify them. There is a lot more than you might have thought about when it comes to these two plants, so we hope this was helpful information for identifying either one.

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Want to know more about how to remove Japanese Knotweed?

Knotweed Removal aims to provide the most up-to-date information, help and advice for YOU to make informed decisions. If you are unsure or uncertain about how to proceed, please reach out to us and we will gladly come back and advise you as best we can.

Governmental advice can be found here and the UK law covering the removal of Japanese Knotweed as stated under the Wildlife and Countryside Act 1981 can be found here.

The best means to contact us is via our email – hello@knotweedremoval.tips

Do not forget we have a library of blogs covering many areas relevant to Japanese Knotweed, our free downloadable How-to Guides and Product Reviews on the latest methods being employed to eradicate or remove Japanese Knotweed.

Knotweed Removal, UK

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