Plants that are mainly non-native are considered invasive by the Weeds Act 1959. An invasive plant can be defined as any plant that grows where gardeners don’t want it to and does it in a way that makes it hard to control.
It doesn’t have to be a weed, and invasive plants are by no means always ugly specimens.
On sale at local garden centres and nurseries, some of the following plants have the potential of taking over large areas and smothering other garden plants.
It is a criminal offence to allow a non-native invasive species listed below to spread into the wild and this carries penalties of hefty fines.
9. Broad-leaved dock
The wind, water, animals, and machinery allow broad-leaved docks to spread over large distances. Infestations can also be initiated by buds growing from broken taproots
Each plant can produce up to 60,000 seeds annually, persisting in the soil “for as long as 50 years”, making complete eradication challenging.
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8. Japanese knotweed
Initially introduced to the UK as an ornamental plant due to its attractive white blossoms that bloom during the warm spring and summer months, Japanese knotweed is now widely distributed and can spread unrestrictedly.
Although the plant cannot propagate through seeds and spread through its root system, its roots are sturdy and rapidly expanding. This invasive weed can significantly reduce property value by up to 20 percent.
Eradicating Japanese knotweed is a challenging task as even a tiny fragment of its root can produce an entirely new plant.
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7. Green alkanet
Green alkanet is an invasive perennial commonly found in shady and damp areas. Despite being grown in gardens for its attractive blue forget-me-not flowers, the plant can “quickly become a weed” when grown under the right conditions.
It is capable of self-seeding, which leads to the growth of new plants close to the parent plant.
Additionally, it can be spread over long distances through animal fur or clothing. It has tall, hairy stems, bristly leaves, and blue flowers with a white centre that opens from a pink bud.
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6. Giant hogweed
Giant hogweed, which can grow up to 10 feet tall, resembles overgrown cow parsley. This is invasive to the UK plant reproduces via its seeds, which are dispersed by birds, animals, and waterways.
Each flower head has the potential to produce up to 50,000 seeds, which can rapidly overrun an area, particularly during floods. The seeds can last for up to 20 years, so control measures must be continued until the soil seed bank is fully depleted, and no further growth is observed.
According to the pros, it is “unlawful to allow this weed to encroach on neighbouring properties”, entitling you to make a legal claim if it has spread to your land.
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5. Three-cornered garlic
This invasive plant, which is “illegal to plant or allow to grow in the UK” has white pendulous flowers which produce large seeds that attract ants.
These ants then spread the plant, allowing it to grow wild along roadsides, banks, verges, hedgerows, woodland and field edges, as well as on waste ground.
Its dense colonies can outcompete other spring flowers such as primroses and violets, and in some cases, it forms dense stands spreading over many metres.
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