How to identify Japanese Knotweed
Japanese knotweed is the UK’s fastest-growing invasive weed. During the summer, it can grow at speeds of 10cm a day. If left untreated, these emerging shoots can quickly exploit weaknesses in brick, tarmac, and metal piping, causing costly damage to everything from buildings to roads.
Attempting to remove the weed yourself will only make the problem worse. Japanese knotweed can re-grow from cuttings as small as 2mm, meaning the smallest traces can lead to new growth. Because of this, knotweed is classed as controlled waste, and must be disposed of safely at a licensed landfill site according to the Environmental Protection Act (Duty of Care) Regulations 1991. By the end of the growing season, Japanese knotweed can reach heights of 4m. At this stage, it is much more difficult to remove.
The first step to treating the weed is with early identification. If you suspect you have Japanese knotweed, we’re happy to help you identify it.
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Japanese Knotweed Identification Guide
Like many plants, Japanese knotweed undergoes growth cycles that can make knotweed identification a challenge across the year. In spring it is identifiable as red buds, emerging into new shoots. These shoots grow rapidly at speeds of up to 10cm a day.
By the time summer hits, the plant’s shoots can reach 2-3m tall. These stalks looks similar to bamboo and you’ll see purple and red speckles on its leaves. Towards the end of the season, the plant produces distinctive white flowers.
The flowers last until late autumn, when they drop. Leaves also start to yellow, then brown, before finally falling off, leaving tall clumps of hollow brown stems.
Knotweed identification is more difficult in the winter. Although the hollow stems above the ground are dead, the widespread rhizome network beneath the ground is still alive and will begin growing again in spring.
Find out what happens to knotweed in winter.
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