Japanese Knotweed: Identification, Prevention, and Removal

Japanese knotweed is a highly invasive plant that can cause significant damage to property and infrastructure. It is native to East Asia but was introduced to the UK in the 1800s as an ornamental plant. Since then, it has spread rapidly and is now considered a major problem in many parts of the country.

Identification

It is a perennial plant that can grow up to 3 metres tall. It has thick, bamboo-like stems and heart-shaped leaves. The plant can spread rapidly by its rhizomes, which are underground stems that can grow up to 7 metres long.

Where knotweed grows

Knotweed can grow in most soil conditions found in the UK, particularly in man-made habitats, such as:

  • roadsides
  • waste ground
  • railway embankments and cuttings
  • spoil tips that are made up of waste material from mining or quarrying

It’s also commonly found along rivers and streams.

How knotweed spreads

Knotweed spreads through:

  • direct rhizome (root) growth
  • new plant growth from the parent plant’s stem and rhizome fragments – a new plant can grow from pieces of rhizome as small as 1cm

If you have knotweed on your land or property

You must stop this plant on your land from spreading off your property. Soil or plant material contaminated with non-native and invasive plants like Japanese knotweed can cause ecological damage and may be classified as controlled waste. You do not legally have to remove Japanese knotweed from your land unless it’s causing a nuisance, but you can be prosecuted for causing it to spread into the wild.

How to stop knotweed from spreading

Do not treat knotweed yourself unless you have the appropriate skills and experience. You can find companies that specialise in treating knotweed.

  • Spray with chemicals Spraying or injecting the stems with chemicals can be an effective treatment to stop knotweeds from spreading. You must only use approved herbicides. You’ll have to respray. It usually takes at least 3 years to treat it. Knotweed rhizome can remain dormant in the soil for many years and will regrow if disturbed or if the soil is relocated. When using chemicals, you may need to:
    • make sure anyone spraying holds a certificate of competence for herbicide use or works under the direct supervision of a certificate holder
    • carry out a Control of Substances Hazardous to Health assessment
    • get permission from Natural England if the area is protected, for example, sites of special scientific interest
    • get permission from the Environment Agency if the plants are near water
  • Physical removal involves using machinery to remove the plant and its rhizomes. This can be a very effective method, but it can also be very destructive to the surrounding area.
  • Biological control involves using insects or other organisms to kill the plant. However, biological control methods are not always effective and can take several years to work.

Preventing the spread of the knotweed is the best way to deal with this invasive plant. If you are planning to buy a property, it is important to check for Japanese knotweed. You can do this by asking the seller for a Japanese knotweed survey. If you find Japanese knotweed on your property, it is important to act quickly to control it.

How surveyors deal with the possibility of Japanese knotweed

When surveying a property, surveyors will look for signs of Japanese knotweed. This includes looking for the plant itself, as well as signs of its presence, such as broken or damaged concrete, fencing, or walls. If surveyors find evidence of Japanese knotweed, they will report it to the buyer.

How Japanese knotweed affects surveys and properties

The presence of Japanese knotweed can significantly affect the value of a property. In some cases, it can even make a property unsellable. This is because Japanese knotweed can be very expensive and time-consuming to remove. It can also damage property and infrastructure.

If you are buying a property, it is important to ask the seller if there is any Japanese knotweed on the property. If there is, you should get a Japanese knotweed survey to determine the extent of the problem. You should also factor the cost of removal into your offer price.