What is Giant Hogweed?: identifying and removing Giant Hogweed from your garden


Though it might look pretty, Giant Hogweed is an invasive plant that has the potential to cause a great deal of harm not only to human health, but also to the environment. This is because it can cause severe skin burns, and prevents the growth of native plants.

First introduced to the UK and Europe in the nineteenth century, Giant Hogweed originally hails from Russia and the Caucasus Mountains in Georgia. In fact, it’s origins in Britain have been traced back to the Russian Gorenki Botanic Gardens, who provided seeds to The Kew Botanic Gardens in 1817; it then became a key feature planted in ornamental gardens throughout Britain, before quickly spreading into the wild.

As a result, Giant Hogweed is now classed as an “invasive alien” in the UK, and this due to the negative effect it has on the growth of native plants, and the resulting impact this has on wildlife. According to the Wildlife and Countryside Act 1981, it’s an offense to cause the spread of these “invasive aliens” in England and Wales. Similar legislation is also in place for the rest of the UK.

Giant Hogweed is also very harmful to human health as the chemicals in the sap cause photosensitivity or phytophotodermatitis (sensitivity to sunlight). As well as severe burns and blistering of the skin, this can also result in pigmentation, and long-lasting scarring.

With Giant Hogweed quickly spreading in the summer heat, it’s essential that you’re able to properly identify, remove and dispose of Giant Hogweed…

How to identify Giant Hogweed

How to identify Giant Hogweed

Cow Parsley (left) vs. Giant Hogweed (right). Image source: Jack Raven Bushcraft

To identify Giant Hogweed, look out for thick purple-spotted stems, as well as coarse white hairs that occur at the base of the stalk. The plant will also have white, flat-topped flowers, which face upwards and are held in umbels.

Giant Hogweed is a very large invasive plant, and its size is one of its defining features. Not only can it reach a height of 5 metres with a spread of around 1-2m, but its leaves are up to 1.5m across, and 3m long. The flower heads can also be as large 60cm across.

One of the main issues when identifying Giant Hogweed is that it’s very similar in appearance to cow parsley (which isn’t harmful). However, there are a few differences, particularly in terms of the leaves and stems. For example, Giant Hogweed has finer leaves, more feathery leaves that are a darker green, and the distinctive purple blotches on their stems. Cow parsley also has hairy stems.

How to remove Giant Hogweed

When it comes to removing Giant Hogweed, you can use both chemical and non-chemical methods to do so. However, if you do choose a chemical treatment, it’s important to remember that Glyphosate-based weedkillers will be the most effective option, as they kill both the roots and top layers of growth.

As the RHS explains, you’ll need to spray the young foliage in May, though you should also be wary of regrowth; this may need to be re-treated in August or September. It may also be advantageous to cut back the plants before spraying the foliage.

How to identify Giant Hogweed

Cow Parsley (left) vs. Giant Hogweed (right). Image source: Jack Raven Bushcraft

To treat Giant Hogweed without chemicals, you can simply remove the seedlings and young plants by hand. The best time to do this is in May, at a time when the soil is moist. You can also let the spike of the flower to form, and remove this before it has a chance to flower.

One of the most important things to remember when removing Giant Hogweed is to wear appropriate clothing to prevent physical contact with its sap. Gloves should definitely be worn, though you should also take care to cover your face; Giant Hogweed can cause temporary and permanent blindness if it comes into contact with the eyes.

Clothing and the tools you use for removal can also be contaminated, so make sure these are cleaned after removing the plant.

How to dispose of Giant Hogweed

Giant Hogweed is classed as controlled waste, so it needs to be properly disposed of after treatment and removal. Although this can be achieved through composting or burning, large amounts should be disposed of in a licenced landfill site.

As the GOV.UK website explains, you can get fined up to £5,000 or be sent to prison for 2 years if you don’t properly dispose of invasive, non-native plants (such as Giant Hogweed and the equally difficult to control, Japanese Knotweed), and allow its waste to spread into the wild.

If you’re concerned about the spread of Giant Hogweed in your grounds or garden, get in touch with PHS Greenleaf; our team will assess the area and provide a bespoke report, before safely removing the Giant Hogweed.