Japanese knotweed

Is a vigorous and invasive plant that spreads rapidly and is hard to kill. It can cause structural damage to buildings and hard surfaces like paths and roads. It can reach over three metres in height and forms dense thickets that kill off other plant life.

Japanese Knotweed spreads via its roots so there is no quick solution to removing it. The roots can spread as far as seven metres around and two metres deep. Trying to dig up the plant often results in spreading the roots and increasing the problem or moving it to new areas. For this reason it is classified as a controlled waste and must be disposed of at a licensed waste site.

What does Japanese Knotweed look like

The plant has large oval green leaves that form on hollow stems similar to bamboo. Cream coloured clusters of flowers appear in July but do not produce seeds that will grow.

The plant starts growing in the spring and by July will form dense thickets of stems, which can be over three metres high. The plant dies back in the autumn, storing nutrients in buds along the roots, ready for rapid growth the following spring.

Cutting the stems in September prevents the plant for taking nutrients back down to the roots and over time weakens them.

Dos and don'ts

If you find Japanese Knotweed on council-owned land, please report it to us and we will take action to control it.

If the Japanese Knotweed is found on private land, we aren't able to take measures to control it, but you should follow the advice below.

Do:

• act quickly, if you find Japanese Knotweed you should act immediately as it won’t go away
• use herbicides safely, follow instructions
• ensure Japanese Knotweed is burned (dried stems only)
• co-operate with your neighbours to control Japanese Knotweed across boundaries

Don't:

• fly tip Japanese Knotweed
• contaminate green waste composting schemes or put in your garden waste sack
• spread out stems and crowns, pile them up on non porous surfaces such as plastic sheeting and allow to die before burning or moving
• spread contaminated soil. Soil within seven metres of plant and up to two metres deep could be infected with possible roots
• add to compost
• break the law, if you cause Japanese Knotweed to spread you could be guilty of an offence under the Countryside and Wildlife Act 1981
  

Removing Japanese Knotweed

With chemicals

The only way to get rid of Japanese Knotweed is to kill the large root system which can take around three years. Spraying over many years appears to be the most effective option. When sprayed the plant may look dead but the underground roots may still be alive. Removing the dead knotweed stems in the winter and spraying the new emerging growth in spring and again in the autumn before the leaves fall is the more effective method.

Glyphosate based herbicides are the most effective or use of an approved contractor who has PA1/PA6 certification could be used to spray the professional and stronger forms of Glyphosate. The cut stems can be burnt on site or disposed of at a licensed tip.

Illegal dumping could result in a fine under the Countryside and Wildlife Act and a breach of fly tipping laws.

Another control method is to cut down growing stems 8-10 cm tall and inject the stumps with 10mm of Glyphosate just before the first growing node. The herbicide needs to be at a concentration of ten times the usual leaf application.

This method avoids the chemical killing other plants in close proximity and uses less chemicals than leaf spraying.

It is also the preferred method where the knotweed is growing amongst plants you would like to keep.

Without chemicals

It is very difficult to remove well established infestations without the help of herbicides. Cutting or mowing with gradually weaken the plant but it could take over five years to exhaust the root system.

You need to cut stems once a month during the growing season. Unless you can burn the cut stems on site, we advise against cutting down the plant, as transporting it risks the plant spreading elsewhere.

Pulling up shoots is more effective because this also disrupts and crown and roots. However this produces the most infectious waste and it must be disposed of with great care. You should stack stems and roots on polythene sheets before burning or disposing of them. If you are storing plant material, you must check it regularly to ensure it is not re-growing and is not able to contaminate water courses. You cannot compost pulled cuttings as they will re-grow.

Responsibility and the law

The Countryside and Wildlife Act 1981 states "It is an offence to plant or otherwise cause the plant to grow in the wild".

Cutting or disturbing the soil if not correctly managed could be an offence. If you allow the plant to spread onto adjacent land it may be considered a nuisance. As the landowner you are responsible and could be sued for costs and damages.

Before attempting to remove the weed you must consider how you will dispose of the cleared plant. Under the Environmental Protection Act 1990 Japanese Knotweed is classed as controlled waste and as such must only be disposed of at a licensed landfill site.

The Household Waste Recycling Centre will not take the waste.