Knot On My Property

“Knot on my property”
A guide to identifying, and solving, a Japanese Knotweed invasion on your property, and other pesky weeds.

Japanese Knotweed or, if we are getting scientific, Fallopia Japonica.

The very mention of it could put the fear of life into any property owners out there. Whilst it is a pest, the good news is that there are options to remove it. The bad news however, is that it has to be done properly or you will have the infestation until the end of your days.

It is easy to get inundated with facts and information on Jap Knot (as we affectionately call it), a simple Google search will prove that. But we have consolidated all the essential information for you to… enjoy, right here. You don’t need to know where it came from* or why it spreads** you just need to know how to identify it and solve it. So grab yourself a cuppa (this is after all a coffee break), and read up.

*The Far East, introduced into Britain in the mid-19th Century as an ornamental garden plant.

** The Rhizome (or underground stem, to you and I)

In a Snapshot:

Is it Japanese Knotweed?

  • Spring – Red / purple shoots, or Asparagus-like ‘spears’ will appear. Initially the red / purple leaves will be rolled up, and will grow in a zig zag formation, with each leaf at a different level from the leaf below / above. Towards the summer season, the stems will develop a distinctive mottled green and purple appearance.
  • Summer – Spikes of distinctive white flowers will appear, and the leaves will unfurl revealing a flat end leaf, similar in appearance to the ‘spade’ suit in a pack of playing cards.
  • Autumn – the leaves will turn brown / yellow. If the plant is undergoing treatment, dead stems (see Winter) will be showing.
  • Winter – The leaves will fall off, and the plant will die back leaving woody stems that turn a pale straw colour. It is more difficult to identify, and cannot be treated, during this season.

See the image below for an RICS image guide to identifying Jap Knot.


Why is it a problem?

  • It is a highly invasive plant, spreading rapidly through even the smallest fragments of the rhizomes. So if you think you can just dump your Jap Knot infected garden waste somewhere else, think again. The reason you have turned to this article is probably because someone did that very same thing years ago, contaminating your soil.
  • It can cause structural damage to your property through its roots and stems; this includes exploitation of existing cracks in pipes, disrupting paving by growing through slabs, undermining garden walls resulting in collapse, growing into outbuildings and conservatories, and spoiling a well-manicured (and expensive!) garden.
  • It is extremely difficult to take control of once established.
  • Some banks refuse mortgages on affected sites.

So what can I do about it?

  • Excavate, though it is an expensive option. Why, you ask? Because that small patch of Jap Knot you have growing in the corner of your garden can go down 3m into the soil and spread 7m across – that requires a lot of digging and digging costs money. As does disposing of the soil in the states landfill site. If this is the route you take, remember to notify the tip operator of the contaminated material so it is buried at the correct depth and cannot regrow.
  • Biological Control. This involves the introduction of a ‘pest’ species that attacks and controls the Jap Knot. This method does not result in the death of the knotweed, but keeps it under control
  • Cultural Control. Many people try to avoid using pesticides or herbicides, so try to get rid of the plant by cultural methods instead, such as cutting, mowing or pulling by hand. This is rarely successful as it takes many years of active regular treatment to weaken and exhaust the rhizome (c. 10 years!). If this is still the route you wish to take, ensure that you dispose of the cuttings carefully or they will spread and haunt you (or someone else) in the future.
  • Chemical Control. This method involves the application of specialised herbicides to Knotweed plants over a period of several growing seasons. This is often the cheapest and most realistic option, however it can still take years to fully eradicate the plant. If this is your chosen route, remember to follow legislation (e.g. Guernsey Water prohibits the use of pesticides within 3m of a watercourse) and get in contact with a specialist. Further information on when and how to treat Jap Knot using this and other methods in Guernsey can be found here.

The information in this Coffee Break article is intended for guidance only. The authors cannot accept any liability for any loss or damage which may result from the use of this article.