Non Native plant species in Ireland

[common invasive non-native plants ]

Japanese knotweed, giant hogweed and Himalayan balsam are three of the most common invasive non-native plants in Northern Ireland.

It forms dense clumps which can be up to three metres in height. It has a hollow stem, similar to bamboo, but is often flecked with dark purple. The leaves are heart or shield shaped and the flowers are delicate and creamy white.

Where it's found

It is now widespread in many habitats, particularly roadsides, riverbanks, railways and derelict land where its movement is unrestricted.

How it spreads

The main way it spreads is through the deliberate or accidental movement of rhizome fragments or cut stems.  It is difficult to control due to its extremely deep root system, which can grow up to three metres in depth and seven metres horizontally.

Tiny fragments of its root, as little as 0.7 g, can produce a plant. The plant can grow as much as two centimetres a day, in any type of soil. It can grow through hard structures such as walls and concrete if there is an existing fault or crack.

Risks to health

It is not harmful to human health.

• Japanese knotweed overview(external link opens in a new window / tab) external link opens in a new window / tab

Giant hogweed

Appearance

Giant hogweed is easily distinguishable from the similar native hogweed and cow parsley due to its sheer height which can reach three to five metres.

Where it's found

It is most commonly found in areas of damp soils, such as river banks.

How it spreads

Each flower head can produce up to 50,000 seeds which are easily dispersed by flood water, meaning it can quickly take over an area. Its seeds can live for up to 20 years, so treatment must be continued until the soil seed bank is fully exhausted and no further growth is observed.

Giant hogweed is listed as an Invasive Alien Species of Union Concern in European legislation, and cannot be sold, exchanged, cultivates or released into the environment. Giant hogweed has been identified as a Widely Spread Species

(external link opens in a new window / tab)

external link opens in a new window / tab in Northern Ireland.

Risks to health

Giant hogweed contains a sap which irritates skin when it is exposed to sunlight. Symptoms are usually noticeable within 24 hours and include blistering and swelling on the skin, which may be made worse by over-exposure to the sun.

If you come into contact with it, cover the affected area immediately to avoid exposure to the sun. Wash the area with cold water. If blistering occurs or the contact was with the eyes, you should seek medical advice.

• How to use your health services

Himalayan balsam

Appearance

Himalayan balsam has pinky red stems with dark green leaves.

Where it's found

It is commonly found in areas of damp soil such as river banks and nearby woodlands.

How it spreads

The plant can produce large quantities of seeds in exploding capsules that can throw seeds several metres away from the parent plant. This enables it to quickly take over the habitat it occurs in.

Himalayan balsam is listed as an Invasive Alien Species of Union Concern in European legislation, and cannot be sold, exchanged, cultivates or released into the environment. Himalayan balsam has been identified as a Widely Spread Species in Northern Ireland