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Many non-native plant species exist in the UK without causing a problem, but a few become invasive. They upset the balance of the ecosystem as they are bigger, faster-growing or more aggressive than the native species. They can often take over gardens and ponds.
There are several steps you can take to stop the spread of invasive plants:
For more information on preventing the spread of invasive non-native plants, visit the Department for Environment, Food and Rural Affairs (Defra) website. You can find information specific to invasive pond and water plants on the ‘Be plant wise’ page.
Four of the most invasive non-native plants are Floating Pennywort, Japanese Knotweed, Giant Hogweed and Himalayan Balsam.
This is also called ‘water pennywort’ or sometimes just ‘pennywort’. It has shiny, kidney-shaped leaves with crinkled edges and is usually found floating on still or slow-moving fresh water. Floating pennywort can grow up to 20 centimetres a day, blocking out light and reducing the oxygen for other plants and animals.
Japanese Knotweed appears to have no natural enemies in Britain and is difficult to control, tiny fragments (as little as 0.7 grams of its rhizome, or root) can produce a viable plant. This plant can grow as much as 2 centimetres per day, will grow in any type of soil, no matter how poor, and can grow through walls and concrete.
The plant forms dense clumps up to 3 metres in height. It has large, triangular green leaves and a hollow stem, similar to bamboo but often flecked with dark red. Japanese Knotweed produces fleshy red-tinged shoots that can reach a height of 1.5 metres by May and 3 metres by June.
You can find out more about this plant and how to control and dispose of it from the Environment Agency, the Devon Knotweed Forum and Natural England (Tel: 0117 959 8622).
Giant Hogweed has a green stem with dark red or purple blotches and spiky dark green leaves. The plant can grow up to 5 metres tall and grows mainly in areas of damp soils, like river banks.
Each flowerhead can produce up to 50,000 seeds, which are easily dispersed by water. Seeds can remain viable for up to 15 years so disposal has to be carried out very carefully.
Giant Hogweed can have adverse effects on skin following contact. Symptoms are usually noticeable within 24 hours, including blisters and swelling on the skin, which may be made worse by exposure to the sun. If you feel unwell after contact with Giant Hogweed, speak to your doctor.
Japanese Knotweed and Giant Hogweed are listed in the Wildlife and Countryside Act 1981. This means that it is illegal to plant it in the wild. Waste from some non-native plants is controlled by law and so certain regulations have to be complied with when disposing of such material.
Himalayan Balsam was introduced into Britain in the 19th century. It has pinky red stems with dark green leaves. It grows fast and can reach 2 to 3 metres in height. The plant can produce large quantities of seed in exploding capsules that can throw seed several metres.
Five particular plants are classified as 'injurious', or harmful weeds under the Weeds Act 1959. These five plants are:
Ragwort is harmful to, and can kill, horses and livestock. All parts of the plant are poisonous.
Contact the National Association of Agricultural Contractors for a list of approved contractors to control harmful weeds - or call 01733 362 920.
It is not an offence to have these weeds growing on your land. However, they must not be allowed to spread to agricultural land, particularly grazing areas or land used to produce animal feed. Natural England may issue enforcement notices to prevent the spread of harmful weeds to agricultural land.
If you suspect harmful weeds are on land near you there are several organisations you can contact:
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