Japanese knotweed treatment: 6 easy ways to treat Japanese knotweed

Timelapse shows alarming rate Japanese Knotweed grows at

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Japanese knotweed is an invasive species which grows so vigorously it can damage pavements, roads and even buildings. The plant is very difficult to get rid of and often involves specialist knowledge. It is an offence to hide the presence of Japanese knotweed and could be deemed private nuisance under common law if you do not inform a neighbour when it begins to encroach on their property.

What is Japanese knotweed?

Japanese knotweed is a nuisance plant which can cause damage to structural foundations including brickwork, tarmac, driveways, patios and drains.

The mischievous plant has a habit of invading and destroying any homes and gardens with which it comes into contact.

New heat maps indicated the destructive plant has invaded many areas of the country, with north-west England, Wales, the Midlands and London being the most overrun places.

Japanese knotweed was introduced into the UK in the mid-nineteenth century as an ornamental plant in parks and gardens and to line railway tracks in order to stabilise the soil.

However, the plant has a notorious habit of growing between important infrastructure causing house prices to plummet by as much as 10 percent.

The plant is in its growth phase during the spring, after hibernating over the winter months.

It is essential to identify and attack this weed early to ensure it does not cause horrendous damage and spread rapidly.

What does Japanese knotweed look like?

Japanese knotweed has highly distinctive rhizomes, which are underground structures that resemble roots.

The rhizomes can prove much more extensive than the above-ground portion of the plant.

Around the spring months, reddish-purple fleshy shoots grow from crimson-pink buds at ground level and can reach more than 2.1m tall.

The canes grown from the plant have characteristic purple flecks and produce branches from nodes along the length.

Japanese knotweed leaves are most often heart or shovel-shaped and can reach 14cm in length.

The stems of the plant die back in cold weather, but the dry canes can remain in place for several months after winter.

In late summer, creamy white flower tassels appear which can reach up to 15cm in length.

Often people mistake Japanese knotweed for other plants such as Russian vine, Himalayan honeysuckle, Houttuynia cordata and Persicaria microcephala.

However, it is very important to identify Japanese knotweed because of the damage it can inflict.

How to treat Japanese knotweed

Japanese knotweed is famously difficult to remove and has to be disposed of at landfill sites alongside other man-made household refuse.

Smother

Covering Japanese knotweed with tarps can help to suppress the growth of this plant and ultimately kill it.

This method is best used during the spring months as it is when the plant is at the start of its growing period.

To successfully smother Japanese knotweed, you should prepare the area by cutting mature weed canes down to the ground and removing any debris.

Next, cover the plant area with tarps, making sure to overlap them so no sunlight can penetrate the stems.

Use rocks and other heavy items to weigh down the tarps so they do not move or blow away.

If new shoots appear, trample them down by walking over the tarps.

Leave the tarps in place for as long as it takes for new shoots to stop appearing.

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Weedkiller control or using chemicals

Typically it will take three or four seasons to fully eradicate Japanese knotweed using weedkiller.

Professional contractors will have access to more powerful weed killer that may reduce this period by half.

You can prevent the spread of Japanese knotweed on your land using chemicals.

You will have to re-spray, which usually takes three years to treat Japanese knotweed until the underground rhizomes become dormant.

You may need to do any or all of the following when using chemicals:

  • Ensure anyone spraying holds a certificate of competence for herbicide use or works under direct supervision of a certificate holder
  • Conduct 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

You may need an environmental permit, waste exemption or trade effluent consent to dispose of certain chemicals.

Cut it

Japanese knotweed can also be effectively treated by cutting it back.

However, this process will not often work to fully eradicate it and must be used in conjunction with other methods.

To cut it down effectively, cut it throughout the growing season, so it is not able to photosynthesise efficiently.

Gather all the cuttings and make sure to dispose of them fully.

Repeat the process as new shoots appear throughout the season.

Dig it up

You can also dig up Japanese knotweed to remove it – which tends to be most effective when used in conjunction with other methods.

Find the rhizome clumps and dig them up.

Try to ensure you find as many rhizomes as possible because anything left behind can sprout a new plant.

Bag these roots for disposal and ensure they are removed correctly.

Bury it

In some cases, you can also bury Japanese knotweed, but you must ensure you are able to do so with the Environment Agency first.

You will not normally be allowed to bury waste on land unless it is at a landfill site which has a suitable permit.

You will be required to bury the Japanese knotweed at least five metres deep, cover the plant remains with a material which prevents it from growing through it and must ensure it is not buried with other types of waste.

Where it is impossible to bury your plant five metres deep, you should wrap a root barrier membrane layer around the plant and ensure it is kept at least two metres deep.

Burn it

You can also treat Japanese knotweed by burning it.

Those wanting to burn it must tell your council’s environmental health officer and the Environment Agency at least a week before doing so.

Those burning Japanese knotweed privately as an individual may not need permission, but should check with your local council first.

Japanese knotweed crown and rhizome may survive burning so you must dispose of any remaining material following the guidance on how to bury or dispose of it off-site.

If none of the above work, you should seek help from a specialist who should be able to treat the Japanese knotweed effectively.

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