How to identify and get rid of giant hogweed safely
Giant hogweed – as architecturally attractive as it may appear on the surface – is not a plant that you want in your garden.
Similar to Japanese knotweed, giant hogweed is incredibly invasive. It grows wild, often lining riverbanks and roads and out-competing native species, which is a problem in itself. What’s more concerning to most homeowners is that giant hogweed also happens to be dangerous when touched.
But if you spot it in your garden landscaping, even though you haven’t planted it, don’t panic. With the right approach, a giant hogweed invasion can be dealt with safely and here’s how.
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Where does giant hogweed come from?
Although not a native species in the UK, giant hogweed has been around for longer than you might think.
“Giant hogweed was introduced to the UK as an ornamental plant in the 19th century,” shares Gemma Rose, invasive non-native species project manager at North Wales Wildlife Trust.
“Giant hogweed (Heracleum mantegazzianum) is a biennial or short-lived perennial invasive non-native species (INNS) originating from Central Asia. It is a member of the carrot family and has since escaped into the wild, where it has become widespread and problematic,” she explains.
Gemma has over seven years’ experience managing invasive plants across North Wales. She leads collaborative, catchment-scale projects, including long-term work across the Afon Dyfrdwy (River Dee) Catchment. Gemma also supports Welsh Government-commissioned initiatives to develop landscape-scale approaches to INNS management.
Identifying giant hogweed
Giant hogweed looks quite similar to cow parsley, and, it also looks – unsurprisingly – like common hogweed, which is why it can be hard to identify if you suspect it in your garden.
“Giant hogweed is high and mighty,” confirms James Ewens, gardening and wildlife expert at Green Feathers. “It is very tall reaching up to five metres, with thick stems marked by purple blotches, large jagged leaves, and wide clusters of small white flowers shaped like umbrellas.”
“Giant hogweed can look similar to our native common hogweed (Heracleum sphondylium) when young,” adds Gemma Rose. “However, when fully grown it is easily distinguishable. As well as its height, it has large umbrella-shaped flower clusters up to 80cm across. The leaves are deeply serrated and hairy, growing up to three metres wide, and the thick stems are marked with dark red-purple blotches and covered in coarse white hairs.”
Overall, as its name suggests, it’s a giant in every sense.
James Ewens is a gardening expert at Green Feathers, the UK’s leading supplier of bird box and wildlife cameras, and passionate about all-things-sustainability and the environment.
Where is it most commonly found?
If you enjoy walking along your local river, you may well have already come across giant hogweed, says Gemma Rose.
“It’s widespread across much of the UK, and is most commonly found along riverbanks, as well as on roadside and railway verges,” she explains. “These environments act as effective dispersal corridors, allowing seeds to spread via flowing water, wind, and vehicle movement. A single plant can produce up to around 50,000 seeds, enabling it to spread rapidly and form dense stands.”
Understanding the dangers of giant hogweed
So why is giant hogweed considered dangerous and does it affect humans and animals?
“The sap of giant hogweed is phototoxic, meaning that after contact the skin becomes highly sensitive to sunlight,” explains Gemma Rose. “This can result in severe burns and painful blistering, with affected areas often remaining sensitive for several months or even years.”
It’s a reaction called phytophotodermatitis which damages your DNA and changes the way your skin protects itself from sunlight. And, if you get it in your eyes, the consequences are equally, if not even more, serious.
“From a wildlife perspective, dense stands can smother native vegetation, reducing plant diversity and limiting food sources for pollinators, insects, and the species that rely on them, such as birds,” adds James.
“Similar effects to humans can occur in animals,” adds Gemma, “particularly on areas with little or no fur. However, some livestock (such as sheep and cattle) have been shown to help suppress growth through grazing, although this should only be considered as part of a managed control approach. For further information, see the Scottish Invasive Species Initiative (SISI).
“If contact does occur, the affected area should be rinsed thoroughly as soon as possible and protected from sunlight for several days (ideally by covering the area),” she advises. “It is also strongly advised to seek medical attention.”
The plant can affect our four-legged friends – both canines and felines – in the same way as well, which is another reason why it’s best to take action if you spot it in your plot or garden design.
How to get rid of giant hogweed
If you’ve spotted giant hogweed in your garden, the most important thing to remember first is to not – under any circumstances – go near it without proper protection. Gloves, long sleeves and pants, safety glasses and a face mask are all advised, with long hair tied well back.
Don’t forget that cut plant debris, contaminated clothing and tools are potentially hazardous too, so be sure to follow all the necessary steps when identifying and removing it from your garden.
“Mechanical methods such as mowing or strimming are strongly discouraged, as they can spread the plant’s sap and significantly increase the risk of skin contact and injury,” warns Gemma Rose.
It’s also not hugely effective – in fact, it can encourage new buds to form on the stalks quickly.
You therefore have three main options as follows:
1. Call in the experts
“Due to the very high risk to human health, management of established giant hogweed should only be undertaken by trained professionals,” says Gemma Rose, “and you can find more guidance on the RHS website.”
A similar approach is typically advised when considering how to get rid of Japanese knotweed too.
But, for smaller cases, or if you think you’ve caught the spread of giant hogweed early on, you do have some options for a DIY approach.
2. Dig it up
The first option you have to is to try pulling, or digging up the giant hogweed. The RHS suggests to do this in May, when the plants have grown tall but are yet to produce their flowering spikes.
“In some cases, smaller plants may be removed by digging out the whole plant and cutting the taproot at approximately a 45-degree angle,” confirms Gemma Rose. “But, this should only be attempted where full protective clothing is worn, with no skin exposed.”
It’s also easiest to do so when the ground is moist, but remember that that the dangerous sap is also found in the roots, so take caution. You can then continue to monitor the area, repeating the process when necessary, until no new growth appears.
3. Use a weed killer
“Targeted herbicide use can be effective for killing giant hogweed,” says James Ewans, “but it needs to be done carefully to avoid harming surrounding plants and wildlife.
For giant hogweed, find an appropriate product that states giant hogweed on the label. This will generally be a systemic, glyphosate-based weed killer, which will tackle the roots rather than just the top growth. These normally need to be applied to the leaves in late spring, then again in late summer if necessary, but check the instructions first.
As the RHS points out, it is worth noting that giant hogweed likes to grow near bodies of water, such as streams or ponds. If this is the case in your garden, it’s best to use an alternative approach rather than this one, as the chance of weed killer entering waterways should always be avoided.
Use these when removing small giant hogweed plants
Ansell
Ansell Alphatec 1500 Model 138, Disposable Work Overall With Hood
This suit is designed to be worn when working with hazardous items. Wear and dispose of once used
Blackrock
Blackrock Safety Goggles
Protect your eyes from seeds with these goggles that can also be worn over glasses
DIY Doctor
DIY Doctor Heavy Duty Gardening Gloves
Thick and strong gardening gloves are a must when removing giant hogweed
How do you prevent it returning?
“Preventing it from returning requires ongoing monitoring and repeat treatment, as seeds can remain viable in the soil for several years. Areas should be checked regularly for regrowth, particularly in spring when growth surges,” says James Ewans.
“Establishing strong, healthy native vegetation can help outcompete any returning seedlings, reducing the chance of reinfestation while also restoring habitat quality for wildlife.”
“Whilst nothing will completely prevent giant hogweed from returning, a combination of repeated treatment and the establishment of dense native vegetation cover is the most effective way to keep it under long-term control,” agrees Gemma Rose.
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Disposing of giant hogweed safely
Like Japanese knotweed, giant hogweed is a controlled waste. This means that it can’t be put in your general trash, nor can it simply be dropped off at your local tip unless it has the correct licence to deal with it. Gemma Rose explains more.
“Under the Environmental Protection Act 1990, giant hogweed is classified as controlled waste. As such, any removal from site must be carried out under strict biosecurity protocols to prevent further spread and to minimise risk to health.
“Where possible, it is preferable to leave plant material in situ to decompose naturally, provided there is no risk of it spreading (e.g. setting seed),” she advises. “This reduces the need for transport and lowers the risk of accidental spread.
“If removal is necessary, material should only be transported and disposed of by authorised persons and must be taken to a suitably licensed or permitted landfill facility, in line with legal requirements. Always consult the relevant Environment Agency guidance for full details,” says Gemma.
“In line with the Be Plant Wise campaign, any on-site composting must be undertaken with extreme care,” she warns. “Composting is only appropriate where it can be done responsibly and securely, ensuring that viable plant material and seeds are fully destroyed and cannot spread into the wider environment.”
“It’s always a good idea to check with your local council when it comes to dangerous, poisonous plants like giant hogweed before you start disposal,” adds James Ewans, “to make sure you are adhering to any specific guidelines they may have in place.”
What to plant once you’ve removed it
“Following the removal of giant hogweed, encouraging the growth of native UK species can help restore the habitat, stabilise the ground, and reduce the risk of it coming back,” notes Gemma Rose.
“Native alternatives such as cow parsley, meadowsweet, or other UK wildflowers are far better options,” suggests James Ewans.
“These plants provide valuable nectar and pollen for pollinators like bees and butterflies, as well as a habitat for insects and small wildlife, and they look lovely. Choosing native species helps support local biodiversity, and maintains a balanced ecosystem without the risk of invasive spread.”
“Purple loosestrife, willow or alder can also provide similar structure and ecological function without the associated risks,” adds Gemma. Prioritising species that are native and well-suited to the local environment will help create a resilient plant community that can better resist invasive species in the future.”
Along with giant hogweed, Japanese Knotweed and bamboo are considered two of the worst offenders in UK gardens. Find out how to identify Japanese knotweed and make sure you understand the laws around growing bamboo before you consider it for screening your garden.
The original version of this article previously appeared on Gardeningetc, a sister website to Homebuilding & Renovating.