Japanese knotweed a growing threat to sales

The TA6 property information form used for conveyancing asks the seller to state whether Japanese knotweed is present on their property. If it is, then the seller must provide a management plan for its eradication from a professional company.

A buyer may be refused a mortgage if it is, or asked for assurances that it will be eradicated before funds are agreed. A management plan by a professional eradication company, backed by a transferable guarantee, is usually required.

Adam Brindle at PCA-approved The Knotweed Experts, which offers 35-year guarantee, says: “Not only will the presence of this pernicious plant stall any sale prospects, it will also devalue a property, in some cases by up to 40 per cent, and make it impossible for potential buyers with mortgages lined up to receive any funding from their lender.

“Some of the biggest mortgage providers are refusing to lend on properties with Japanese knotweed because its extensive roots can penetrate deep into the ground, damaging house foundations, drainage system and walls.”

Barclays demands that buyers call in an expert who is a member of the Property Care Association and who offers a ten-year insurance-backed guarantee against the plant's return. If it has been discovered within seven metres of the home, the bank won't offer a mortgage until the work has been done.

The Royal Horticultural Society say that Japanese knotweed dies back to ground level in winter but by early summer the bamboo-like stems emerge from rhizomes deep underground to shoot to over seven feet, suppressing all other plant growth.

According to the RHS, in spring, reddish-purple fleshy shoots emerge from crimson-pink buds at ground level. These grow rapidly and in summer they produce dense stands of tall bamboo-like canes. These canes have characteristic purple flecks and produce branches from nodes along their length.

Leaves are heart or shovel-shaped and up to about five inches in length and are borne alternately in a zig-zag pattern along the stems. The stems die back to ground level in winter but the dry canes remain for several months. The creamy-white flower tassels produced in late summer and early autumn reach up to six inches.

“The problem with Japanese Knotweed is that in late spring and throughout the summer it can grow at an astonishing rate, by 40 cm a week easily, and its underground root system can grow at least three metres deep,” says Adam, who adds: “There isn't a really good DIY solution to eradication. You need to get someone in because of the specialist chemical treatment or, in some cases, controlled excavation or incineration required to get rid of it. It is controlled waste, which means you have to take it to a dedicated licensed facility.”

It is not illegal to have Japanese knotweed in your garden, but you must control the plant to prevent it becoming a problem in your neighbourhood.

According to the Anti-social Behaviour, Crime and Policing Act 2014 if it has a “detrimental effect of a persistent or continuing nature on the quality of life of those in the locality”, then legislation could be used to enforce its control and property owners may be prosecuted.