Gardeners have been warned to keep an eye out for nine illegal plants that could cost them thousands of pounds in fines this summer.

With more than 50,000 infestations of Japanese Knotweed recorded across the UK, garden experts are warning homeowners to keep an eye out for the unwanted visitor.

However, it is not the only plant we should be wary of welcoming into our gardens this year.

People have been fined thousands of pounds for allowing illegal plants to grow in their gardens, but many homeowners don’t know how to spot them.

Jack Sutcliffe, co-found of Power Sheds, said: “Once you can identify the most common criminal plants, it’s important to prevent them from spreading as soon as possible.

“The easiest way to do this is by spraying them with chemicals, digging them out or burning them.” 

The garden experts have listed the top criminal plants that can grow in gardens, as well as the fines homeowners could face for having them.

Japanese Knotweed

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The Japanese knotweed is one of the most invasive plants. It has bamboo-like stems and clusters of small white flowers which can cause significant damage to property and infrastructure. It is difficult to eradicate once established, making it even more important to avoid in your garden. 

If you’ve spotted the Japanese knotweed growing in your garden, it’s important to get professional help to remove it, as even the smallest piece of stem left in the ground can regrow. If you’re selling a property, make sure to get a professional survey done by an RICS surveyor. This will help protect you from any legal action from buyers if knotweed is later discovered on the property. 

Fines for the Japanese knotweed can go up to £34,000, but a recent lawsuit against a seller whose property had the plant came to £200,000.

Spear Thistle

The spear thistle is a noxious weed in the UK and it is currently illegal to allow it to grow in your garden. The plant has spiky leaves and purple flowers and can spread quickly, causing harm to crops and other vegetation. If discovered, the fines for it can cost up to £2,500.

Common Ragwort

The common ragwort is easily recognisable with its bright yellow flowers and feathery leaves. Although it is one of the most common weeds, this toxic plant is harmful to livestock, with the fine for growing this illegal plant up to £5,000.

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Broad-Leaved Dock

Similar to the spar thistle, the broad-leaved dock also harms crops and vegetation. It can easily spread across the UK as it’s not sensitive to weather conditions. The plant can be recognised by the broad leaves and spikes of small yellow flowers. If they are found in your garden, you can be fined £2,500.

Curled Dock

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Another noxious weed, the curled dock, has distinctive curly leaves and spikes of small yellow flowers. It can spread quickly and is a flexible weed. Fines of up to £2,500 can be given for allowing it to grow on your property.

Rhododendron Ponticum

Growing to considerable heights, the Rhododendron Ponticum is another invasive plant on the list; it will even compete with other plants for a little bit of sunlight! The plant has evergreen leaves and large clusters of pink or purple flowers, and is poisonous to vegetation and wildlife. It is difficult to eradicate once established, making it even more important to avoid growing it, otherwise you could face a £5,000 fine.

Himalayan Balsam

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While it can look pretty, don’t be fooled by the Himalayan Balsam! Perhaps one of the quickest to spread, each plant has around 800 seeds that are easily transported by wind, animals, or water, and will grow again. The plant has spikes of showy pink or purple flowers, and fines can go up to £2,500.

Giant Hogweed 

This toxic plant is harmful to humans, as its chemicals can cause significant wounds to the skin. While for some, it is just a burning sensation, for others, it can cause permanent scars. This is why giant hogweed is considered illegal and the fines can go up to £5,000. They can be recognised by their large white flowers and towering height. 

New Zealand Pigmyweed

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Known for killing the other plants you might be trying to grow in your garden, the New Zealand Pigmyweed poses a threat to everything around her. It’s an invasive plant and the sales of this seed have been banned since 2014. The plant has small green leaves and clusters of tiny white flowers, and it can harm even aquatic environments. If found guilty, you could face a fine of up to £2,500.