The presence of non-native invasive plant species in the UK poses significant challenges for biodiversity, ecosystems, and the economy. While many non-native plants integrate without issue, a select few become invasive, spreading rapidly and outcompeting native flora. This page defines what is considered an invasive plant species, examines how they spread, the impact on biodiversity, legal obligations, and effective control methods. For those needing guidance on identification and management, links to PBA Solutions’ resources have been included to support the responsible control of these species.
Invasive Plants Definition
Invasive plants are species not native to the UK that spread rapidly and disrupt local ecosystems. These plants, sometimes referred to as ‘alien invasive plant species’, can outcompete native species for resources, often resulting in reduced biodiversity and altered habitats. Unlike other non-native plants, invasive species pose significant environmental and economic threats.
In 2023 the GB Non-native Species Secretariat estimated that invasive non-native species cost the UK economy around £1.9 billion a year. Most of the 2,000 plus plants that have been introduced to the UK pose no harm, but 10-15% of them go on to be categorised as an ‘invasive non-native species’.
How do Invasive Plant Species Spread?
Invasive plant species spread through various mechanisms that enable them to establish dominance over other vegetation. Some, like Japanese knotweed, rely on rhizomes—underground stems that can grow horizontally and form new shoots. Other species, such as giant hogweed, produce large quantities of seeds that are easily dispersed by wind, water, or animals. Himalayan balsam, meanwhile, can spread rapidly due to its unique explosive seed pods that project seeds over a wide area.
Human activities also play a significant role in the spread of these species, often unintentionally moving seeds or plant fragments in contaminated soil, equipment, or vehicles. Japanese knotweed is sometimes spread as a result of fly tipping or the use of unscreened soil containing fragments of Japanese knotweed rhizome.
Invasive Plant Species List
The plants listed in the table below are land-based ‘species of special concern‘. In addition to the plants below there are currently another 10 invasive alien plant species that live in water habitats (not listed here).
| Common Name | Scientific Name | Habitat |
| Asiatic tearthumb | Persicaria perfoliata | Land |
| Balloon vine | Cardiospermum grandiflorum | Land |
| Broomsedge bluestem | Andropogon virginicus | Land |
| Eastern baccharis | Baccharis halimifolia | Land |
| Giant hogweed | Heracleum mantegazzianum | Land |
| Golden wreath wattle | Acacia saligna | Land |
| Japanese hop | Humulus scandens | Land |
| Kudzu vine | Pueraria lobata | Land |
| Perennial veldt grass | Ehrharta calycina | Land |
| Sosnowsky’s hogweed | Heracleum sosnowskyi | Land |
| Tree of Heaven | Ailanthus altissima | Land |
| Whitetop weed | Parthenium hysterophorus | Land |
| Common milkweed | Asclepias syriaca | Land |
| Crimson fountaingrass | Pennisetum setaceum | Land |
| Chilean rhubarb | Gunnera tinctoria | Land |
| Japanese stiltgrass | Microstegium vimineum | Land |
| Vine-like fern | Lygodium japonicum | Land |
| Chinese bushclover | Lespedeza cuneata | Land |
This list is accurate at time of posting (30th October 2024), but is periodically reviewed. Minsters from the governments of England, Scotland and Wales make decisions on recommendations provided by the GB Committee for Invasive Non-native Species. Balloon vine, pernnial veldgrass, whitetop weed and kudzu vine are sheduled to be delted from this list due to their inability to establish themsleves under current UK climate conditions. However, 5 other plant species are being considered for inclusion.
UK Invasive Plant Species Identification
Thankfully, many of the UK’s non-native invasive species possess distinct features that can aid in identification, even for those less familiar with these plants. Identification typically involves visual examination of key parts, such as leaves, stems, or flowers; however, growth habits also provide important clues. It’s worth noting that certain plants, like giant hogweed, should not be approached due to health risks.
To help with the identification and understanding of the most common invasive plant species in the UK, PBA Solutions provides dedicated identification pages on its website. These resources offer detailed descriptions, key invasive plant identification features, and guidance on managing the species. Below are links to individual plant profiles:
Can Native Plants be Invasive?
Although most native plants support local biodiversity, certain species can exhibit invasive tendencies under specific conditions. For example, bracken (Pteridium aquilinum) is known for its rapid spread, especially in disturbed areas, where it can limit biodiversity by overwhelming other vegetation.
Some plants listed under the Weeds Act 1959, known as injurious weeds, spread rapidly across pastureland used for grazing livestock. Species like common ragwort (Senecio jacobaea) and creeping thistle (Cirsium arvense) reduce the quality of grazing land and pose risks to livestock health. Effective management is essential to maintain productive farmland and protect animals.
Creeping thistle spread across a field in South Wales
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How do Invasive Plants Affect Biodiversity?
Invasive plants disrupt biodiversity by outcompeting native species, often with severe ecological consequences. Dense, tall growth from plants like giant hogweed (Heracleum mantegazzianum) blocks sunlight, restricting the growth of smaller plants beneath and reducing the diversity of vegetation in an area. Species such as Japanese knotweed (Fallopia japonica) and Himalayan balsam (Impatiens glandulifera) contribute significantly to soil erosion. Both species die back during the winter, leaving riverbanks and slopes bare and vulnerable. Without the stabilising presence of plant roots, soil weakens and becomes more prone to erosion and sediment runoff.
Additionally, some invasive plants, such as Rhododendron ponticum, impact ecosystems by altering soil composition. This species releases chemicals into the soil that inhibit the growth of other plants, effectively creating a monoculture where only the rhododendron thrives. Such chemical changes make it difficult for native flora to survive, allowing the invasive species to spread unchecked. This imbalance affects the entire ecosystem, as fewer native plants mean reduced resources for insects, pollinators, and animals that rely on them for food and habitat. Over time, these impacts reduce the resilience of local ecosystems, leaving them more vulnerable to further environmental stressors.
Invasive Plants and the Law
UK legislation includes several laws aimed at controlling invasive species and reducing their impact:
Species of Special Concern
This list identifies species whose impact on biodiversity requires significant control. The species included are subject to restrictions to prevent their import, sale, growth, or release in the wild. Derived from the ‘List of Union Concern’ plant species in the EU Regulation (1143/2014) on the prevention and management of the introduction and spread of invasive alien species. This became a Retained Regulation following the UK’s exit from the EU, but now applies only to Great Britain.
The Invasive Alien Species Order 2019
The Invasive Alien Species Order 2019 complements existing legislation, adding measures to control the spread of non-native invasive species. It introduces more stringent regulations, including restrictions on importing, keeping, and selling invasive species. Created to support enforcement efforts and to meet the needs of the Retained Regulation.
Schedule 4 (PART 1) of the Act amends Wildlife and Coutryside Act 1981 to remove 7 notable water plants and the following land-based species from Schedule 9:
- Himalayan balsam (Impatiens glandulifera)
- Giant Hogweed (Heracleum mantegazzianum)
- Giant rhubarb (Gunnera tinctoria)
These species are now listed instead in PART 2 of The Invasive Alien Species Order 2019.
The Wildlife and Countryside Act 1981
A cornerstone piece of UK legislation for the conservation of native species and habitats. It makes it an offence to release, plant, or allow the spread of certain non-native species in the wild, particularly those listed under Schedule 9. These restrictions are designed to protect local ecosystems from the ecological and economic harm invasive species can cause.
Schedule 9: lists species, notably Japanese knotweed, that cannot legally be introduced or encouraged to grow in the wild. This provision supports the control of invasive plants, reinforcing the responsibility of landowners to manage these species responsibly and prevent their spread.
How to Remove Invasive Plants
Effective removal of invasive plants requires methods tailored to their mode of spread, such as seeds, corms or rhizomes. For seed-producing species, like giant hogweed, it is vital to act before seeds are dispersed to prevent further spread. Since seedbanks can remain viable for years, repeated treatments or surface scraping may be necessary. For rhizome-spreading plants, such as Japanese knotweed, careful attention to biosecurity is essential to avoid unintentionally spreading plant fragments to neighbouring properties or other areas.
Montbretia spreads via corms, which are similar to bulbs but are actually adapted stems
A combined approach often works best, incorporating herbicide treatments alongside physical removal. This not only tackles the immediate infestation but also addresses regrowth potential. Professional assistance is recommended for large-scale or resilient infestations to ensure thorough and compliant management. Improper handling of plants like giant hogweed can pose serious health risks, highlighting the importance of expert intervention.
Proper disposal of invasive plant material is equally important. In the UK, invasive plants listed under Schedule 9 of the Wildlife and Countryside Act 1981, such as Japanese knotweed, are classified as ‘controlled waste’ under the Environmental Protection Act 1990. This classification requires these materials to be transported and disposed of at licensed facilities, following strict guidelines to prevent further spread. Failure to comply with these regulations can result in fines or legal action.
Combining targeted removal, repeated treatment, and responsible disposal ensures effective control of invasive plants while minimising their long-term impact on ecosystems.
Contact Us Today
For professional assistance with the identification, treatment, and removal of invasive plants, contact PBA Solutions. As accredited PCA invasive weed specialists and experts, our team are trained and experienced in dealing with invasive plant species growing in diverse locations. If you’ve recently become aware of the plant, and you are concerned about its spread, get in contact today. Call our experienced team on 0203 174 2187 or 01202 816134 for advice, information on site surveys and our comprehensive management plans.