The invasive Japanese knotweed – that has been known to grow eight feet in a single month to take over gardens and even threaten house foundations – is rife throughout Kent.

A study of reported infestations has found Tonbridge to be the worst place in the county, closely followed by Sevenoaks and Tunbridge Wells.

There are 58,000 known infestations of the UK’s most invasive plant across the country – 63 of them are in Tonbridge and 51 each in both Sevenoaks and Tunbridge Wells.

Japanese knotweed usually emerges in March or April and grows rapidly to reach up to 2.5 metres in height by mid-summer. It is identifiable by its hard, bamboo-like canes and distinctive shield-shaped bright green leaves which grow in a zigzag pattern along the stem.

Mature plants flower in August, becoming covered in clusters of delicate tasselled creamy-white flowers.

Knotweed does not produce viable seeds as all the plants in the UK are female, so it is usually spread accidentally through the movement of soil or gardening waste, or via rivers and streams when pieces of root stalk break off and take hold in new locations.

Tackling knotweed costs the UK economy nearly £250 million a year and homeowners are one of the groups most at risk – not only from potential damage to their property, outbuildings and gardens, which can be costly to repair, but also from legal risks arising from encroachment on neighbours or when properties are sold.

While it is not illegal to have knotweed growing on your land, it is illegal to allow it to cross a boundary into an adjacent property, which can be very difficult to prevent.

Similarly, when properties are sold, sellers are asked a direct question about whether knotweed is present, even if hidden beneath the ground or within three metres of the boundary, and those who fail to declare it can be sued by their buyer for misrepresentation.

The presence of knotweed in your garden could seriously reduce the value of your home when selling.

Environet is a company specialising in its removal, and other invasive species.

Company founder Nic Seal said: “Vigilance is the best way to protect your property from the risks posed by Japanese knotweed.

“Make sure you know what knotweed looks like and how it differs from other common garden weeds like ivy and bindweed, so you can keep an eye out for it in your garden and neighbourhood.

“Knotweed is easily identifiable during summer, but as we head through the autumn and into winter, the above-ground growth dies back and it becomes much harder to spot. It’s also easier to conceal, so anyone viewing a property to buy should be extra careful.”

Environet has produced a map showing knotweed infestation in the county.

Readers can go online here and type in their postcode to discover how many knotweed infestations are within 4km of their home.