How to identify and kill Japanese Knotweed.

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What is Japanese Knot-weed?

Description for Japanese Knotweed

  • Japanese Knotweed is a non woody stemmed plant that grows up to 12 feet high.
  • The stems look like bamboo canes. They can be up to 2 inches thick.
  • It can grow as much as an inch per day.
  • The leaves, grow to about to 6 inches long. They are an ovate shape, pointed at the tip with flattened bases  and hairless on underside. See the Japanese Knotweed picture.
  • The cream-white flowers grow in panicles from July through to the autumn.
  • The root system can extend several yards around and under the base of the plant.
  •  Roots are white and soft, maturing to dark brown and knotty. The inside  is pale yellow to bright orange with a darker core.

Problems and damage caused by Japanese Knotweed.

  • Spreads easily and can regrow rapidly from less than 1 inch of root.
  • Out competes our native wild and garden plants.
  • Very difficult and expensive to control or eradicate. 
  • Can grow through and break-up tarmac and concrete and cause structural damage to properties. 
  • You can be fined up to £2,500 for failing to control it.

breaking news

People who fail to control the spread of invasive non-native plants such as Japanese Knotweed could be fined or receive anti-social behaviour orders the government says.


Japanese Knotweed is a very invasive weed, originally brought in from Japan.  

Introduced in the nineteenth century as an ornamental plant, it escaped into the wild and is now a costly problem, not just for gardeners. Left unchecked, it will invade large areas of land, takeout native plants, break up concrete, block paving ruin clay ponds and canals, and damage buildings.

If you have Japanese knotweed growing in your garden. 

Japanese Knotweed growing in your garden, can potentially cause major problems, not only to your own garden and property, but to neighbours gardens and properties.  I have listed a few tips and actions you should take to control the spread of Japanese knotweed. 

What is the law regarding Japanese Knotweed?

The Wildlife and Countryside Act 1981 says,  it is an offence to plant or grow Japanese knotweed  where there is any risk of causing the plant to spread into the wild or neighbouring properties.  

It also states that it is up to you the householder to control the plants from spreading. It is also illegal  to dispose of Japanese Knotweed incorrectly, causing further spreading. I have included safe and legal ways of disposal on this page.

If  you see Japanese knotweed growing in neighbouring gardens or on council property, try explaining to your neighbour, the potential damage to the countryside and property this will cause if left untreated.  If reason fails or you spot Japanese Knotweed growing wild. The police have a wildlife liaison officer who can be contacted.

How does Japanese Knotweed spread? 
It spreads through its crown, rhizome (underground stem) and stem segments but, can occasionally be spread by seed and can grow a metre a month. 
Once it has spread under concrete, tarmac or block driveways,  It causes heave below the surface and grows up through the cracks, damaging buildings and roads.  Root segments can remain dormant for up to  twenty years in soil, before producing new plants, a tiny section can produce a new plant in 10 days.

how to kill and safely dispose of Japanese Knotwood

 

Clearing Japanese Knotwood using weed killers
 
I find the most effective weed killer to eliminate Japanese Knotweed  is Glyphosate, it's applied directly, by painting the leaves and is taken in by the plant to the roots and kills the whole plant.
First cut away the old stems (and burn them) to get at the new growth. The best time to apply Glyphosate is in late summer, but this will be difficult as the knotweed would have grown to around 7 feet. A much easier way is to paint on the Glyphosate when the Japanese knotweed has reached about  3ft,  and apply a second application in mid summer and again in September.
  
Check the infestation again the following spring. Glyphosate treated knotweed will sometimes produce small leafed, bushy regrowth about 20in in height the following spring. Treat this in the same way.
 
How long will it take to eliminate Japanese Knotweed from a garden. 
Up to five years, but if you are vigilante and repeat the above process, as soon as you see new growth, you might get rid of the pest within a shorter period.
 
Non chemical control of Japanese knotweed
Japanese Knotweed is used to feed animals in some parts of the world, so if you keep goats let them graze the infested area.  Grazing will help reduce the spread into uninfested areas and control growth but will not eradicate the Knotweed.   You could of course let the goats do the hard preparation work, leaving only the stems and then follow up with the weed killer treatment. 
Best and cheapest way of killing Japanese knotweed

When I'm treating a large area of Japanese Knotweed, I use this concentrated 360g/l weedkiller, rather than the branded sprays, it is a lot cheaper and a lot more effective. More information on my page

Always check Strength actually is 360g/l when buying concentrated Glyphosate weed-killer from other sources

Disposing of Japanese Knotweed.

First contact your local council, they may offer a collection service or have a list of sites that accept Japanese knotweed waste. If you are going to dispose of the Knotweed yourself, its irresponsible to dump it anywhere, it could regrow, its also illegal!!  Any plant or soil material to be disposed of off site should be securely bagged to prevent spillage. When you leave the area of your garden contaminated with Japanese knotweed, check clothes and shoes, making sure no plant or soil material is present. It is easily spread to other parts of yours and neighbours gardens.

Do not put it on your compost heap or anyone elses for that matter.
Do not leave it out for the council to collect as recyclable waste.
 
Controlled burning is the best and safest way to get rid of Japanese Knotweed
Private householders can burn Japanese knotweed waste under controlled conditions in the garden.
Store the green stems and leaves on a ground protection sheet until they dry out and then start a bonfire and gradually add them to the fire. It's important to burn every bit to ash. Get rid of the dangerous  pest forever.

Finally a few precautions when dealing with an infestation of Japanese Knotweed.

  • Dont use a strimmer, this will spread it.
  • If you cut it down dispose of it by burning in your garden. Material taken away must be safely contained and disposed of at a licensed disposal site.
  • Digging it up will lead to a significant increase in stem density. Even a tiny bit will start new growth.
  • Don't spread soil contaminated bits of root. Any soil that is obtained from ground within 7 m of it could contain root that is highly regenerative. 
  • When purchasing locally recycled loose topsoil ask your supplier for a guarantee it does not contain bits of knotweed root.
  • Mechanical chippers don't kill it. If you spread the chipped material on soil it will regrow.
  • Never add it to your compost heap.
  • Don't dispose of Japanese Knotweed at garden waste recycling centres, it will contaminate the compost.
  • Don't dump contaminated garden waste in the countryside.
  • Don't waste time. If Japanese Knotweed appears in your garden, treat it immediately. Don't allow it to become established.
  • Don't break the law. Remember, if you cause Japanese Knotweed to spread you are guilty of an offence under the Wildlife and Countryside Act, 1981.

Latest news

People who fail to control the spread of invasive non-native plants such as Japanese Knotweed could be fined or receive anti-social behaviour orders (Asbos), the government says.

The weed is one of the most destructive plants in the UK.

The new rules mean people can now be fined up to £2,500 for failing to control it.

And companies who fall foul of the law can be fined up to £20,000.

The Home Office says these plants threaten the UK's biodiversity by crowding out native species and destabilising riverbanks. They can also do immense harm to forestry, farms, roads and buildings.

Japanese knotweed can grow through tarmac and cause structural damage to properties, 

Japanese knotweed is particularly difficult to eradicate. It is very resilient and regrows vigorously after being cut down.

The most effective method of eradicating it is by using herbicides in the late summer or autumn, when it is close to its flowering sta

ge.

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