The Japanese Knotweed is a quick-growing plant! It yearly comes up from the ground, and produces a thick-dense 10-12 foot tall screen. In mid-September, it produces a lovely display of white flowers, that attracts bees, and finally in October, when hit by a hard-killing frost, dies back to the ground. At that time, you take a really good pair of branch clippers, and cut it back to the ground, as CLOSE as possible. The Japanese Knotweed does not continue growing on the previous years growth, it ALWAYS dies back to the ground.
Over the years, the Japanese Knotweed snuck under the fence, and worked its way out to the street. It grew in the lawn, and even sent out roots under the poured cement foundation of the garage. Somehow, it resurfaced, through a crack, in the corner of the garage floor, where the foundation, and poured cement floor meet.
After a while, it was time to control, and hopefully eliminate the Japanese knotweed. Being that it was growing in clay soil, trying to dig it out would be too big a project, and it had migrated a distance. So my ONLY solution was to tame it with the lawn mower.
First of all, the Japanese knotweed does not give up, and die easily! So in early spring make sure any remnants of the previous year’s growth is cut as close to the ground as possible. You will be running your mower over that area, and do not want to hit any old stumps of the plant.
Starting with the first grass cutting, or when you see it starting to appear, WEEKLY cut it down with the lawn mower, close to the ground as possible. The Japanese knotweed is persistent, and will send up many consecutive shoots, trying to establish its ability to collect light (photosynthesis). From the beginning of spring, to almost late summer, it RELENTLESSLY tries to establish growth, since you are STARVING it of LIGHT. Only toward the end of “eradication season one”, will it start to slow down a little.
The following year, “eradication season two”, of the Japanese Knotweed, do exactly what you did in “eradication season one”. Cut it down weekly, don’t let any part of it establish growth, and STARVE it of sunlight. It will still try vigorously to send up shoots all season long.
Only in the middle, to end of “eradication season three”, after doing the steps of seasons one and two, will you start to see a marked change. The Japanese knotweed will start to slow down, the growth will be a lot less vigorous, and a lot weaker. I am on “eradication season three” inside the fence, and at about eradication season five, outside the fence, where it is almost non-existent. Hopefully in the next few years, I will have tortured, and killed off everything.
One more thing, a few times each season, I tried to get it with Roundup. It burnt the leaves, but really did not weaken the plant much.
So tell me, do you have the invasive Japanese knotweed on your property, and how have you tried to eliminate it?