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Bringing knotweed under control

This invasive weed can cause structural damage to homes if allowed to get out of control. It’s easy to see why Japanese knotweed (Fallopia japonia) made its way into UK gardens at the start of the Victorian era, says Amateur Gardening’s Kris Collins. It’s such a striking architectural plant that you could almost forgive the plant hunters for bringing to our shores - that is if you don’t have it growing in your garden!

Anyone trying to eradicate what is now classed as the UK’s most invasive plant will know how hard it can be to bring it under control and despite it being a notifiable plant (one that can do extensive damage when released into eco systems and should be reported to local authorities) local councils can offer no help to private land owners. So if it’s in your garden it is up to you to deal with it.
Glyphosate is considered to be the best chemical control against this weed, though a more heavy-duty approach is needed than a simple ready-to-use spray bottle.

An initial hit is needed to weaken the plants defences. Commercial contractors use specialist injections systems to place the herbicide directly into the plant. I’ve come up with a nifty DIY version (below). Following this initial application professionals then revert to regular spraying through the season - most claim to be able to rid the problem in one season.

If you prefer to stay clear of chemicals you can regularly prune the plants, removing all foliage and preventing the plant from photosynthesising. Alternatively you can dig out the roots and surrounding soil and hope you have taken up all traces of the plant. However, prunings and soil can not be used for home or local authority composting. If you have Japanese knotweed appearing in your garden follow the steps below as soon as you can!

Step by step
DIY chemical injection

1) I took the smallest funnel I could find and glued it to an empty biro casing to create a thin nozzle for getting the chemical into the plant.
2) Mix Bayers’s Tree Stump Killer as directed and allow to sit and dissolve - mark up any containers clearly to avoid contamination.
3) Cut all stems below the lowest leaf joints to reveal the hollow stems
4) Insert the funnel into the plant stem and pour a small amount of the mix down in the plant. Repeat for all stems. Revert to spray mixes for further treatments through the year.


Knotweed and the law
Neither the Environment Agency or local authorities are responsible for dealing with knotweed on privately owned land. However most councils are responsible for dealing with the plant if it is growing on roadside verges and public land. Alongside larger main roads it usually falls to the Highways Agency to deal with the problem.

If Japanese knotweed makes it into your garden from a neighbours plot there is little support for your rights under current legislation. The best solution is to work with your neighbour to come up with a solution, perhaps sharing herbicide costs.

Since the plant can re-grow from even small fragments, all parts of the plant and any soil contaminated with it are classified as controlled waste and are required legally to be removed and disposed of by a licensed waste control operator. To keep costs down home disposal should consist of burning all parts. For further advice on knotweed control visit www.environment-agency.gov.uk or call 08708 506 506.