The Threat of Japanese Knotweed

A few years ago I discovered an outbreak of Japanese Knotweed right in the village in Staffordshire where I live. Once I became aware of it I kept finding it in all sorts of places, even on the continent in Europe when travelling on holiday.

This was the first time I had come into contact with the weed, or even heard of it. After some research on the Internet and various discussions with officers at the District Council and County Council, I realised what a particularly dangerous weed this was. Not dangerous to human beings but to the native flora of the countryside. It grows so vigorously and densely that it can literally suffocate smaller species in its path.

"You have to stand in amongst it to realise its awesome potential."

It is so invasive that it is controlled under the 1981 Wildlife and Countryside Act, which made it illegal for anyone to spread Japanese Knotweed. It will easily propogate from pieces of stem, rhizome (root), or crown (base of stem) with fragments as small as 10m/m long!!
Luckily the seeds are normally sterile, but the roots can extend as far as 7 metres radius from the parent plant including vertically downwards and new shoots can then sprout up anywhere within that area. Once established it can grow up to 2.5 to 3 metres tall and by as much as 10cms A DAY!

I am particularly anxious to avoid the accidental spread of this obnoxious weed, so I am seeking to publicise the potential dangers as much as possible.

The weed was originally introduced into this country by the Victorians. What a legacy they have left us. Some of the worst areas affected in the UK are to be found in Cornwall and in Wales.

There is a vast amount of information on the Internet, a useful link if you would like to find out more can be found by clicking HERE


With great difficulty. However regular systematic cutting back of top growth will eventually kill off the root system. It must be a regime that continues relentlessly over a very long period, if you relax it will start gaining strength again and your previous efforts will be totally wasted. This method of attack can over a period of time kill the plant.

If you cut back top growth and then wait a few days until there are very bright new red leaves you can reinforce your attack by applying "ROUNDUP" (from your local Garden Centre) to the leaves and this will then quickly get into the root system as this is a systemic system of weed control. Roundup should be used with care especially if you have plants nearby that you would like to keep.
As the root system is so invasive DO NOT ATTEMPT to DIG IT UP, the roots can reach up to 7 metres away and go as deep as over 3 metres. Disturbing the roots will stimulate new growth. The smallest piece of plant material can under suitable conditions quickly regrow into a new plant.
You can still burn garden refuse on a bonfire, providing you do not create black smoke or inconvenience the neighbours. I suggest  that any material that is cut down should if possible be safely kept in a dry place and then when dry burnt on a very hot bonfire, so as to produce little smoke and to make sure it is all burnt. Please consider neighbours before lighting a bonfire.
UNDER NO CIRCUMSTANCES put Knotweed into your rubbish bins, this is potentially dangerous and could spread the weed on your local landfill site very quickly. It is also illegal as you would be allowing the weed material to 'escape' from your property!
If you cannot burn your Knotweed waste then special disposal arrangements should be available with your local council.

As the plant top growth naturally dies over the Winter be especially vigilant the following Spring. If necessary start the control regime again, until you have won.

I am still finding out new information on this issue.
So I will be posting additional details on a regular basis if I think that they will help to control this problem.

Updated  1/11/07

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