There are a range of invasive plants which can pose a threat when they ‘escape’ from gardens in the UK. Some of these you can’t legally grow in the UK (or can only do so with serious restrictions). Species of particular concern include:
This is a severely problematic invasive, non-native perennial. It grows quickly and forms clumps, spreading by rhizomes below the soil. It can regrow from even very small sections of rhizome, though it will rarely set seed in the UK. So it can easily spread and quickly take over an area, outcompeting native plants and damaging ecosystems.
Though it was originally introduced to the British Isles as an ornamental plant, it is now very controlled. It is an offence to cause Japanese knotweed to grow in the wild. And if you are selling your property, you need to check the garden and report Japanese knotweed if it is present.
It is not illegal to have it in your garden, but you can be prosecuted if you fail to aim to keep it under control, allow it to spread, or do not get rid of it correctly. Since this plant is very difficult to eradicate on your own, it is best to approach a specialist company.
Himalayan Balsam (Impatiens glandulifera), is another invasive plant. It is related to Busy Lizzie but grows above head height. It is a major weed problem on riverbanks and vacant lots. And can also be a problem in allotments and gardens. It grows very quickly, outcompeting and smothering other vegetation. Seeds spread via waterways and wind, or human means. It is illegal to plant Himalayan balsam or introduce it to the wild.
Rhododendron ponticum was first introduced to the UK in 1763 and today, it spreads far beyond gardens, causing damage to woodlands and meadows across the British Isles. The bushes excluse sunlight from ground cover plants, and smother many other plants and trees.They are also toxic to some animals and the plant also carries diseases which can kill our native tree species. It is illegal to plant this, or allow it to grow in the UK.
Similar to cow parsley and common hogweed – but much larger, Giant hogweed is able to grow 10 feet tall. The plant’s sap contains chemicals which cause burns and blistering when they react with sunlight on human skin. It spreads though seed, and can outcompete other plants becoming a serious problem along waterways. And a danger in areas of human habitation. It is illegal to plant or allow this to grow in the wild in the UK. To eradicate this from your garden, as with Japanese knotweed, it is best to consult a professional company.
This is an aquatic plant which was introduced to UK garden ponds, but which has now become established in the wild with serious ecological consequences. It forms dense mats of rounded leaves which cover the surface of waterways, depleting oxygen levels and reducing light for photosynthesis. It outcompetes many native plants and impacts many aquatic animal species. A single tiny portion of this plant floating off downstream can quickly turn into a whole new raft of vegetation.
New Zealand Pygmyweed or Australian swamp stonecrop, this is another non-native pond plant which causes massive ecological harm in our waterways. It was banned from sale in the UK in 2014. As with the above, it chokes out other aquatic life and can spread from just a tiny stem fragment.
Another aquatic plant whose sale was banned in 2014, this water fern is another highly invasive species, which has spread from garden ponds and now causes a lot of damage to aquatic flora and fauna in British waterways.
American Skunk Cabbage
Previously on sale as a pond margin garden plant, this has caused many problems due to its escape from gardens out into the wild. This plant has large, leathery leaves and bright yellow flowers. Its seeds spread along waterways and are likely also spread by wildlife. When dense stands of this plant occur in the wild, their large leaves shade and outcompete many other native species, damaging riparian habitats. And it can spread very quickly once it gets a foothold in an area. It was banned from sale in the UK in 2016.
Gunnera tinctoria (Chilean rhubarb) is a popular garden plant. It is commonly grown beside ponds or in damp areas, prized for its exotic look and huge leaves. But as of 2017, it is an offence to plant or cause this plant to grow in the wild in the UK. It can spread and dramatically alter wild ecosystems, and as an ecosystem engineer, can alter environments and outcompete many other species. Where it is already present, steps should be taken to control it.
Curly waterweed was commonly sold for garden ponds. But this is another invasive water plant which is on the invasive species list. It is an offence to plant or cause this plant to grow in the wild. In the wild, this plant has spread very quickly and is another aquatic non-native causing harm in British waterways.
Another aquatic plant banned from sale since 2014. It is a popular pond plant forming mats of feather-like leaves. Like other plants on this list, it can spread and root from even the tiniest fragments and choke up waterways and fresh water bodies in the wild.
This is another popular garden pond plant, which is illegal to plant or cause to grow in the wild. This is another oxygenating pond plant which grows quickly, and when it escapes into the wild, can outcompete native species and damage biodiversity in British waterways.
These are just some invasive plants – and there are many more which cannot be grown or must not be released to the wild in the UK.
When choosing plants for your garden, it is important to consider the impact of the plants you choose – not only in your own space, but also in surrounding ecosystems. Avoid non-native, harmful invasive plants at all cost.
As gardeners, we have a role to play in keeping our environments safe. And that includes being very careful about what we grow, and how we manage existing invasive plants in our gardens.
Elizabeth Waddington is a writer and green living consultant living in Scotland. Permaculture and sustainability are at the heart of everything she does, from designing gardens and farms around the world, to inspiring and facilitating positive change for small companies and individuals.
She also works on her own property, where she grows fruit and vegetables, keeps chickens and is working on the eco-renovation of an old stone barn.
To get in touch, visit https://ewspconsultancy.com.