Native to East Asia in Japan, China, and Korea, japanese knotweed has established itself around the world. The World Conservation Union lists it as one of the world's most invasive species due to its aggressive root system and its ability to completely take over environments – so much so that in the UK and Scotland, it is actually illegal to plant or grow it. Japanese knotweed can damage all manner of modern architecture, from roads to foundations to buildings. Its roots grow so deep and re-sprout so vigorously that removing japanese knotweed is nearly impossible.

Once the weeds start to flower and fructify, it will be difficult to control them effectively. In fact, the best time to remove weeds is before flowering and fructification because the seeds will spread rapidly after that. So, it is necessary to remove weeds more often and to take precautions in advance next year. Mulching: First, trim the plants at the ground level. Because the stem is sharp and can penetrate most of the materials, choose nonflexible materials (such as concrete slab) to carry out mulching. Make sure not to leave any gap in between slab to prevent them from growing again. Pulling out and Chemical control: Before the weeds fructify, wear gloves or use tools to pull them out. The rhizome can extend 7 m horizontally and reach a depth of 3 m, which makes it very difficult to remove through digging. Therefore, when using herbicide, you can choose glyphosate to add to the stem to kill the root system. The parts that are above-ground need to be controlled repeatedly for several years. In fact, it is discovered that herbicide is the most effective at the flowering stage in late summer or late autumn. Note: When removing weeds, it is necessary to wear gloves to avoid direct contact with the weeds, especially for the ones that are poisonous, thorny and allergenic. When removing weeds at the flowering stage, special masks should be worn to prevent allergic reactions caused by the inhalation of pollen.