Parks and Green Spaces

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 tall 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.

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.

The Countryside and Wildlife Act 1981 states ‘It is an offence to plant or otherwise cause the plant to grow in the wild’. This means that 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.

If the Japanese Knotweed grows across boundaries we advise both parties to act. 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.

Where it is found on council owned land we will take appropriate action to control it spreading.

The council is not obliged to control Japanese Knotweed on behalf of other land owners. Shared problems between neighbours need to be tackled jointly.

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 of eradication.

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 which has a maximum penalty of £50,000.

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

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.

The local amenity tips are not licensed to accept such waste and will refuse to accept this material. The landfill sites are also unwilling to accept Japanese Knotweed from private gardens. The city council offers a Japanese Knotweed collection service for which there is a small charge. The reason for this charge is that Japanese Knotweed is a polluted material and as such must be disposed of through special arrangements with our waste disposal contractor. Please email parks@southamtpon.gov.uk to arrange for a visit and quote for disposal. The city council does not offer an eradication programme just a disposal route.

Do act quickly, if you find Japanese Knotweed you should act immediately as it won’t go away.

Do use herbicides safely, follow instructions.

Do ensure Japanese Knotweed is burned (dried stems only).

Do co-operate with your neighbours to control Japanese Knotweed across boundaries.

Do tell us of infestations on council owned land.

Do not fly tip Japanese Knotweed.

Do not contaminate green waste composting schemes (the green waste bin at the tip) or place in green garden waste bags.

Do not spread out stems and crowns pile them up on non porous surfaces such as plastic sheeting and allow to die before burning or moving.

Do not spread contaminated soil. Soil within seven metres of plant and up to two metres deep could be infected with possible roots.

Do not add to compost. Compost separately so you can be sure it’s fully broken down before re-use.

Do not break the law. If you cause Japanese Knotweed to spread you could be guilty of an offence under the Countryside and Wildlife Act 1981.

Visit the Environment Agency's website.

Leaf clearance takes place during the autumn and winter with additional resources allocated during October to January.

During October to January area teams have a programme of leaf clearance that prioritises areas of heavy leaf fall and areas prone to flooding.

Leaves are left in shrub beds as a natural mulch.

It is up to residents to clear and dispose of leaves from their own property responsibly.

Find out about the garden waste collection service in Southampton.

The council is responsible for clearing leaves from council land but you can help look after your local area by clearing leaves.

If there is a build up of leaves outside of the leaf clearing programme (October to January) please contact the council on 023 8083 3008 or email sparkling@southampton.gov.uk.