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Problem of Invasive Plant Species in the United Kingdom

Updated on June 4, 2017
Giant Hogweed
Giant Hogweed

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Invasive Plant Species in the British Isles

Did you realise that invasive plants could be such a big and expensive problem? Even though the United Kingdom is an island country, it has still been invaded by many introduced plants. Many of these alien plants have been accidentally introduced by gardeners, as many of them produce seeds that can easily find their way into the open countryside or people do not dispose of plant cuttings safely and these then propagate in different locations.

Invasive plant seeds can also arrive in this country in crop seeds, packaging materials or hay bales. It is believed by conservationists that invasive plant species are one of the major causes of environmental decline and the extinction of native plant species.

They compete with our native plants and crowd them out of their habitats. They can quickly spread out of control because they may not have any natural predators in the United Kingdom and are also not affected by local plant diseases.

They also cause problems for native animals and insects, as their foliage can be unpalatable to them, thus negatively impacting food supplies if an invasive plant species takes over an area. In some cases these invasive plants can even cause harm to humans as they can disrupt water supplies and ruin crops.

Eradication programmes are often very difficult and the costs of undertaking them can run into millions of pounds. Some invasive plant species can also cause structural damage to roads, buildings and flood defences. In the United Kingdom,

The Wildlife and Countryside Act 1981 contains Schedule 9 Part II which lists all the invasive plants that it is against the law to plant or allow to propagate in any way in the wild.

Japanese Knotweed
Japanese Knotweed | Source

Japanese Knotweed

Japanese knotweed is an invasive plant species in the United Kingdom and it has the power to destroy buildings, weaken flood defences, break through tarmac and this invasive plant also strangles and suffocates our native plant species.

Japanese knotweed came to Great Britain from Japan during the nineteenth century courtesy of Victorian gardeners, and has managed to invade every part of the British Isles since then. Currently only the Orkney Islands are free of Japanese Knotweed. It is an invasive plant that is listed on Schedule 9 and it is an offense to plant or cultivate Japanese knotweed in the wild.

Japanese knotweed grows extremely quickly and it can shoot up to as much as 9ft in just a few months. Japanese knotweed will grow in most environments but prefers to grow by waterways. This invasive plant has very sturdy roots and once established Japanese knotweed is extremely hard to eradicate, as it can regrow from the smallest piece of stem that is left behind. It has been estimated that in the United Kingdom around £1.6 billion is spent annually trying to get of it.

There are no natural predators for the Japanese knotweed in the UK as there are in Japan, and although the knotweed is relatively common in its native county it does have predators that control its spread. In an attempt to contain the spread of Japanese knotweed, the Department of for Environment, Food and Rural Affairs (Defra) is proposing to introduce one of these predators of into the UK from Japan.

This predator is a type of jumping and sap sucking plant louse called Alphalara itadori, a type of psyllid. A five year study on the effects of this psyllid on 87 native British plants has been undertaken by the Centre for Agricultural Biosciences International and the scientists say that this introduced predator would bring the Japanese knotweed under control without causing any problems to native species.

However, predators introduced to control native pests or invasive species have not always been successful and in the case of the cane toad, introduced into Queensland, have themselves become significant problems for the native flora and fauna of their host countries.

Floating Pennywort in Foudry Brook
Floating Pennywort in Foudry Brook | Source


Rhododendron was introduced into Great Britain in 1763 from Southern Europe to bring some colour to the grounds of big country estates and to produce some ground cover for game. As it creates dense thickets, it blocks out the light for ground plants.

It is an evergreen shrub and its leaves cannot be eaten by most of our native animals and insects. Rhododendron also poisons the soil through its root system, as their roots creates toxins in the soil that stops other plants from competing. They also makes the soil around where they are planted acidic. Rhododendron spreads rapidly and crowds out native plant species.

These introduced shrubs are causing particular concern in important oak and hazel woodlands in the west of Scotland, where rare moss and lichen populations are being put under threat. An eradication programme for rhododendron was introduced on the island of Lundy in the Bristol Channel when they began to threaten the endemic Lundy Cabbage. However, it costs a great deal of money to eradicate rhododendron and just in the Snowdonia National Park alone they have spent more than £45 million attempting to do so.

Floating Pennywort

Floating pennywort was introduced into the UK from New Zealand in the 1980’s, and a lot of gardeners bought it for their ponds. As it grows it forms a thick mat of vegetation on the top of the pond water which starves the water of light and oxygen and it can also cause flooding by blocking sluices. This kills any fish that live in the pond. It spreads very rapidly when it gets into a new waterway and can grow up to 30cm a day. Floating pennywort competes for the habitat of many of our rare and endangered aquatic native plants, as it completely takes over when it it finds its way into a natural lake or pond.

Himalayan Balsam

Himalayan Balsam was originally introduced into the UK as a garden plant in the nineteenth century. It has spread to many regions of the UK and is found mainly on the banks of rivers and streams. Himalayan Balsam is very difficult to eradicate as it has an explosive seed head that can catapult its seeds up to four metres away from the plant.

These seeds often end up in rivers and streams and can be carried great distances before they wash up and start growing and contaminating other stretches of riverbank and land.

It is also a very tall invasive plant, so it shades out and crowds out many of our native species. The Himalayan Balsam also produces a lot of nectar and is attractive to pollinating insects, which is causing concern that this invader is attracting bees to the detriment of our native flowering plants.

Giant Hogweed

Giant Hogweed was introduced into the British Isles in the mid-eighteenth century from Central Asia. It greatly resembles our native hogweed, but it grows to a much larger size as it can grow to be between 5 and 7 metres in height. It is now found throughout much of Britain and tends to grow near watercourses. It has a toxic sap that can irritate skin just by brushing against it. The Giant Hogweed sap will also react on the skin in sunlight and this can cause intense blistering of the skin.

So the protection of our native plant and animal species involves ensuring that no further invasive species of plants are allowed to find their way into our countryside and that the invasive plants that have already established themselves are either eradicated or controlled successfully.

Gardeners need to be aware of the list of plants on Schedule 9 and garden centres and retailers who sell plants need to be vigilant that they are not selling these invasive plants. If anyone is having problems caused in their gardens or damage happening to their homes because of a plant like Japanese knotweed, there are companies that will come in and professionally eradicate them for you.

Giant hogweed Image is from Andrew Smith and licensed for reuse under this Creative Commons Licence

Japanese knotweed image Migas Creative Commons Attribution Share Alike 3.0 Unported

Floating pennywort image Simon Mortimer Creative Commons Share Alike 2.0 Generic

© 2010 CMHypno


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    • CMHypno profile imageAUTHOR


      8 years ago from Other Side of the Sun

      Hi Nicky, Japanese knotweed is a particular nightmare to eradicate and if left unchecked can cause a lot of damage. Thanks for reading the hub on invasive plant species and leaving a comment

    • Nicky Smart profile image

      Nicky Smart 

      8 years ago from United Kingdom

      Interesting hub, thanks. I have noticed lots of Japanese Knotweek along the banks of the rivers and the canal near my home. It seems such a heavy task to try to keep it down.

    • CMHypno profile imageAUTHOR


      9 years ago from Other Side of the Sun

      Hi PaperNotes, I think the worry over these invasive plant species is the damage they are doing to the native plants. It's a difficult problem, and one that most countries of the world are facing. Thanks for reading the hub and leaving a comment.

    • PaperNotes profile image


      9 years ago

      Interesting hub. As they say, all things created by God have its purpose on earth. I suppose that we only think of them as nuisance because we have not thought of any useful applications for them yet.

    • CMHypno profile imageAUTHOR


      9 years ago from Other Side of the Sun

      Glad that you found the hub on invasive plants in the UK interesting leni sands. Japanese knotweed is a big problem in this country and can be both expensive and dificult to eradicate.

    • leni sands profile image

      Leni Sands 

      9 years ago from UK

      Interesting hub, thanks. I have noticed lots of Japanese Knotweek along the banks of the rivers and the canal near my home. It seems such a heavy task to try to keep it down.

    • CMHypno profile imageAUTHOR


      10 years ago from Other Side of the Sun

      hypnodude, I think it would be a great idea to find a use for invasive plants after they have been dug up. The big worry is how these alien species affect our native plants and animals and how much they are changing the landscape. Unfortunately it's a worldwide problem. Thanks for visiting the Hub and leaving a great comment.

    • hypnodude profile image


      10 years ago from Italy

      This is interesting. I think the best way to deal with them is to find a use for them, if possible. At least like green mass to burn to produce energy. But I agree with you, no one wants the same problem Australia had with rabbits and the solutions applied to get rid of them. It's a pity that they are not edible. Great informations CMHypno.

    • CMHypno profile imageAUTHOR


      10 years ago from Other Side of the Sun

      Glad you enjoyed the Hub on invasive plant species, Hello,hello and thanks for leaving a comment

    • Hello, hello, profile image

      Hello, hello, 

      10 years ago from London, UK

      Thank you for your interesting informations.


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