What is Japanese knotweed?
Japanese knotweed (Fallopia japonica), as its name may suggest, is a plant species that originates from eastern Asia. It’s thought to have been introduced to the UK in the 1840s, to be used both as an ornamental garden plant and a cattle feed.
At first, farmers and horticulturalists were enamoured with the weed, with influential gardeners including William Robinson encouraging its use through their writings. But come the turn of the 20th century, perceptions of the species were changing, and its rapid and unruly growth saw it fall out of favour. Unfortunately, this realisation came a little too late. By the early 1900s, Japanese knotweed had ‘escaped’ its managed gardens and plantations and was now growing in the wild right across the UK.
What does Japanese knotweed look like?
Japanese knotweed is a ‘perennial’ plant, meaning it lives for several years, growing and blooming through spring and summer before dying back come autumn and winter.
It begins its (visible) life cycle as a small shoot, red and green in colour and similar to asparagus in appearance. As the shoot grows taller through spring, it becomes greener, with only red speckles remaining. Growing into a bamboo-like stem as much as three metres tall, this will then sprout an abundance of shield or elongated heart-shaped leaves, initially red but turning to a bright green. At maturity, these leaves will be roughly hand-sized, while the stem will be noticeably hollow and easy to snap.
Around September each year, Japanese knotweed will sprout small white flowers all over, sometimes covering the plant almost entirely. It’ll then begin to drop its flowers and leaves around November time, reducing to a browning and brittle stem that will eventually collapse. Once spring comes back around, the plant will re-emerge from its roots in the very same spot as before.
Why is Japanese knotweed a problem?
Like any plant or tree which isn’t well maintained, Japanese knotweed is notoriously eager to branch out into neighbouring properties which can cause issues when it comes to conveyancing.
Growing as much as six centimetres a day at its peak, and with the ability to break through cracks and hard surfaces, this beautiful but brawny plant has the strength to penetrate property foundations, roads or walls.
Japanese knotweed is unique in the sense that it has almost no natural predators in the UK, leaving the pruning to homeowners as opposed to nature. As a result, it’s estimated that Japanese knotweed damage, management and removal costs the UK as much as £166 million each year and to help reduce this number, it’s now against the law to introduce this weed in the wild.