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Japanese Knotweed Invasion - How To Get Rid Of It

Japanese Knotweed (Fallopia Japonica) is one of the most destructive invasive plants we have in Ireland right now.

It has heart or shield shaped leaves, hollow bamboo stalks which grow in a distinctive zig-zag pattern, red or red flecked diamond shaped stems that grow in very large clumps and can be up to three metres tall.  It is an herbaceous perennial plant which means it dies down but comes back every year.

I was first introduced here as an ornamental plant in the 1900's because despite its destructive nature it is actually quite a pretty plant and it attracts a lot of bees. By the time it was realised how damaging it was it was already too late and it had gotten a firm hold here in Ireland. 


It outgrows all of our other native plants and so will quickly engulf an area. It is hugely damaging to our hedgerows, completely smothering all other species of plants. 

The roots have the ability to grow through tar and concrete and have been known to destroy the foundations of houses. 

If you have it in your garden close to your house in any sort of substantial way when you go to sell it can significantly affect the price of your house once a surveyor spots it. 


So why have we not gotten rid of it? Well, we have tried. 

The issue is Japanese Knotweed is fantastic at spreading itself. Its roots are made up of Rhizomes that can grow as deep as it can tall. Its root system has been known to go up to three metres deep and through whatever lies beneath whether it be drainage pipes, concrete foundations, or steel gridding so it is incredibly hard to get it out. 

Then there is how easily it can survive. If you spot it and try to remove it yourself the smallest bit (1cm long piece) dropped will produce a healthy and vigorous new plant. 

It is insanely fast growing also. It can grow up to 10cm a day which is nearly unbelievable (I triple checked that fact!). 


So how do we get rid of it?

Well first and foremost, if you do spot it, do NOT cut it or try and strim it. This is the number one way you can spread it further in your garden. 

Don't disturb the soil around it's roots or in the near vicinity. 

The best method of control we have is sadly chemical. If it is a relatively small plant you can treat it with a glyphosate based weed killer such as Resolva Pro Weedkiller Super Concentrate Xtra Tough 1l. It will take multiple applications and quite possibly over a few years but it will eventually kill it. You can also smother the plant in conjunction with using spray. Simply cover the area with a tarp or any large bit of light blocking plastic such as a bin bag. This will stop the plant's ability to photosynthesise and starve it. 


It is illegal to dump any Knotweed infested soil in a non-licensed area. 


If you spot Japanese Knotweed growing in a public area such as a roadside hedgerow it is important that you get in touch with the local county council and inform them. They will register it and send out a specialised crew for its removal.