Not only can Japanese knotweed make your home unsellable, but it could also cause issues when remortgaging.

This is what Nasreen Akhtar discovered when trying to sell her terraced house in Birmingham. Japanese knotweed had taken over her neighbour’s garden and caused potential buyers to run a mile.

“This highlights another reason to always invest in a property survey when buying a new home” comments Dan Lowery MRICS, Director of Romans Surveyors. “Our team of RICS qualified surveyors are trained to look for faults or concerns that the untrained eye cannot spot, such as damp, subsidence and knotweed.”

Of course, depending on the time of year and the level of growth it isn’t always possible to spot Japanese knotweed, so you should always seek advice from a surveyor if you're concerned about it being present in or near your own property. They will be able to ascertain the level of damage that has occurred and offer advice.

All you need to know about Japanese knotweed

The ornamental plant from Japan has been causing problems across the UK since it was first brought over in the 19th century. The invasive nature and the speed at which Japanese knotweed grows are the main problems, as it finds its way through drainage systems and through cracks in concrete.

What does Japanese knotweed look like?

Purple shoots start to appear in early spring and the plants are fully grown by early summer. The more mature plants can grow up to 3m in height and the distinctive canes carry a purple speckle. In late summer through to early autumn Japanese knotweed flowers with 15cm tassels of white blossoms. Once the leaves have fallen off the canes die and turn brown, but often remain standing.

Buying a house with Japanese knotweed

“If Japanese knotweed is suspected the advice is to get a specialist in to confirm the extent and course of remediation as this can be costly and take a number of years” adds Dan. “The presence of knotweed could also affect the mortgage ability of a property.”

Some building societies decline mortgage applications on properties where Japanese knotweed is present, however “in practice, it's not usually a problem as long as a remediation plan is put in place,” says Sue Anderson, spokesperson for the Council of Mortgage Lenders (CML).

It's estimated that it would cost £1.5 billion to completely remove Japanese knotweed from the UK. But currently, specialist agencies are working with local councils, homeowners and mortgage lenders to devise treatment plans, backed by warranties, to help property sales continue to proceed.

Dan Lowery

 

How do you get rid of Japanese knotweed?

Managing and removing Japanese knotweed can, unfortunately, be very challenging. The Royal Horticultural Society states on its website: “eradication requires steely determination.”

  • Excavation of Japanese knotweed

Infested soils can be taken to an appropriately licenced, off-site waste-management facility. Because of the way the weed spreads the area of soil needed for evacuation can spread up to 3m deep and 7m wide, resulting in very large volumes of waste soil.

It is possible to excavate and bury Japanese knotweed on-site. If there isn't space to cover it with 5m or more of overburden a specialist root barrier membrane will need to be installed, to prevent any regrowth.

  • Attacking Japanese knotweed

One way to keep Japanese knotweed in check and to prevent it from spreading is to introduce a biological control. A 'pest' species can be used to attack and control the weed.

  • Chemical control

Applying a specialised herbicide to Japanese knotweed plants is one of the most economical treatment methods; however it can take years for this method to be effective. If space is limited and there are closely located property boundaries, like in most residential settings, this is the most realistic option.

If you've found Japanese knotweed in your property and you're not sure how to effectively treat it always talk to a professional surveyor, who will be able to measure the magnitude of the problem and estimate the cost of treatment.

Interesting facts about Japanese knotweed

  • It was introduced to Britain in the 19th century as an ornamental plant
  • It can grow up to 10cm a day and its underground root systems can stretch for 7m
  • It spreads through its rhizome (underground stem) rather than its seeds
  • Rhizome can be dormant in soil for twenty years before growing new plants
  • It is an offence to plant or cause Japanese knotweed to grow in the wild
  • It can grow through house floors and cracks in concrete
  • Japanese knotweed is used as a traditional medicine in Japan
  • Organisers for the London 2012 Olympics spent four years trying to control the weed, at a cost of approximately £70 million
  • Other names for Japanese knotweed, include: donkey rhubarb, Mexican bamboo and Hancock's curse
  • Landowners are not legally obliged to remove Japanese knotweed, unless it is causing a nuisance to neighbouring property

Although this non-native, invasive plant can be difficult to control, timely and persistent treatment programmes can minimise its impact. As the treatment industry continues to develop new, more effective treatments will become available for homeowners. Also, as lenders adopt more consistent policies; Japanese knotweed should soon become just one more consideration in the complex valuation process.

Romans Surveyors & Valuers has more than 20 years' surveying experience and is a member of the Royal Institution of Chartered Surveyors (RICS). For more information or to request a survey, visit romans.co.uk/surveyors, email surveyors@romans.co.uk or call 0333 1220 961.