Japanese knotweed (Polygonum cuspidatum) is one of the worlds most invasive plants which can wreak havoc in lawns and gardens
Japanese knotweed plants were introduced from Japan first into the UK in the 19th century as a landscaping ornamental and it soon spread like wildfire.
It’s often found in sunny, moist areas, including riverbanks, roadsides and your lawn or garden. It only takes one fragment of one root to takehold and crowd out other plants in the space.
So how do you get rid of Japanese knotweed plants?
1. Weed Killer
The weed killer recommended for use against Fallopia japonica is glyphosate. Trade names include Gallup, Landmaster, Pondmaster, Ranger, Roundup, Rodeo, and Touchdown.
The weed killer is sprayed on Japanese knotweed’s foliage, however, you can also inject into the stem. The best time to use weed killer is late summer or early autumn, when the plant is flowering and the foliage is conducting the most nutrients to the rhizome to build food reserves. Some people have success spraying repeatedly throughout the growing season, never giving the plants a chance to put on much height.
2. Cutting back
Cutting back the plant throughout the summer supresses growth. Remember as cuttings easily sprout new roots and re-entrench themselves, pick up the cuttings and bag them afterwards.
Don’t rely on the cutting method in isolation, though. Cutting back Japanese knotweed regularly is a tactic only meant to be used in conjunction with injections of weed killer into the cane stumps. But this is a lot of work — and certainly not the preferred method.
3. Japanese knotweed rhizomes can be dug up and bagged.
Dig into the ground where the bamboo shoots come up most vigorously. You will probably discover the rhizome-clumps from which Japanese knotweed’s roots and shoots. Rhizome-clumps are very woody and can easily reach widths of a foot or more. Note; as some of the rhizome roots will snap off an from even the tiniest root of Japanese knotweed left in the ground, a new plant will eventually emerge.