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Which? Trusted trader tips for getting rid of Japanese knotweed

By Lauren Merryweather

Japanese knotweed is an invasive plant that spreads rapidly, stunts the growth of other plants, and is notorious for causing damage to buildings. Our Which? Trusted traders share how best to manage it.

Japanese knotweed is difficult to remove, but failure to control its growth on private or commercial property could lead to being fined, and can even prevent potential buyers from securing a mortgage.

This tough, perennial species grows fast during the spring and summer, preferring borders, flower beds and roadsides, but it will spread just about anywhere. Its bamboo-like shoots may reach up to 7ft in height before dying back in the winter months. Although the presence of Japanese knotweed at a property is not illegal, if it’s allowed to grow out of control or spread into neighbouring property, those responsible could be prosecuted under the Anti-social Behaviour, Crime and Policing Act 2014.

If you’ve got a problem with Japanese knotweed in your garden, our Which? Trusted Traders-endorsed tree surgeons or gardeners can help you manage it.

Taking action against Japanese knotweed

Steve Bannon from Which? Trusted trader Japanese Knotweed Eradication explains why it’s essential to deal with it quickly:

  • Japanese knotweed spreads through regeneration of live material such as cuttings and roots. This is exactly how it spreads so quickly and, when it does, it takes over, preventing other plants and vegetation from growing.
  • If you suspect you have Japanese knotweed on your property, don’t touch it or disturb nearby ground, and that means absolutely no gardening. The area must be quarantined.
  • The spread is relentless. For example, people often dispose of what they think are harmless garden cuttings into compost bins, and later spread compost containing the knotweed all over their gardens. Another common cause of spread is when small pieces of the plant get attached the clothing or equipment of gardeners as they move between jobs, demonstrating how prolific this plant can be.
  • There is no one-off treatment; it’s a case of managing growth long term, with a lot of perseverance. Getting professional help really is the best way to make sure it’s done thoroughly.
  • It’s a bit of a myth that Japanese knotweed can destroy a well-maintained property. However, it is certainly known to take advantage of any structural weaknesses. If there is a space for it, it will grow.

Japanese knotweed is so destructive that homeowners must report its presence to their solicitor when they intend to sell. Mortgage lenders will want to see a long-term management plan prepared by a professional. A knotweed professional or specialised tree surgeon will also be able to carry out assessments and produce a risk report that will be required for legal and mortgaging purposes.

Handle knotweed with care

Trusted trader Derek Farley CSJK, of Evergreen Landscape and Building Services Ltd, explains the long-term treatment process:

  • The aim is to destroy the plant’s complex and deep root system, or rhizome. They can grow to 10 metres in depth - one of the reasons knotweed is so stubborn.
  • A powerful herbicide is mostly used in populated areas. Herbicide may be applied to the leaves, but one of the most effective methods is injecting the stems of the plants. This treats the knotweed directly without affecting other nearby plants and trees.
  • Standard treatment plans span three growing seasons, over three consecutive years. 
  • Once the treatment is complete, property owners will still need to continue closely monitoring the area for any new growth for at least another two years.
  • There are strict guidelines on disposing of Japanese knotweed trimmings. It’s classified as hazardous material, and normal waste-disposal sites will not accept cuttings or ‘dead’ plants. You will need to dispose of it at a specialist site that can bury and contain it. A professional will be able to take care of this, legally.
  • There are lots of horror stories and old wives’ tales about Japanese knotweed being indestructible but, in reality, most cases can be successfully treated.

Suspect you have Japanese knotweed in your garden? Contact a professional Japanese knotweed removal service in your area.

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