Q: How can we get rid of Japanese Knotweed, my understanding is that if I try to remove it, there is a risk it will further spread, and so treating it is the best solution?
A: Don’t dig it as it spreads by roots, not seed, and any disturbance just makes it regenerate quicker. It’s very difficult to get rid of but with time it can be dealt with.
The conventional way to treat it is with chemicals, but that can take a spray in spring and again in summer for up to three years to completely kill off.
Some companies do stem injections which work faster but it’s laborious and costly. If you cut back now and wait a few weeks until it starts to regenerate then a spray will undermine more of it as it has just of expended lots of energy to put up new shoots.
Chemical free options are to keep cutting it back to ground level every few months to burn up its root reserves (the stalks and foliage are compostable and even edible – a delicacy in japan and a medicinal source of resveratrol in China).
The final option is to starve it: cover it with weed membrane, tarp, polythene, old carpets — whatever will keep the light out. If it has no sun it can’t photosynthesise and so has no energy to grow, after a year its roots will start to wither away and it won’t be able to regenerate.
— Fiann Ó Nualláin @holisticg
Photo credit: Picture taken by gerald_at_volp_dot_com. Child in foreground is about 90cm in height. Via Wikimedia Commons
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