What Is Japanese Knotweed? All Information About This Plant

What is Japanese Knotweed? It is a very aggressive weed capable of causing significant damage to property. It has small white flowers and bamboo like stems and can grow up to 10 cm a day. It is a nasty weed that finds masonry cracks and weak points to go through and this can cause significant damage to buildings.


What Is Japanese Knotweed? How Did It Get Here?

Japanese Knotweed is native to Korea, Japan, and parts of East Asia as well as China and was brought to the UK in 1850 by Philipp von Siebold, a German-born botanist on the wave of popularity that was surging through Victorian Britain to collect and study plants from different parts of the globe.

Japanese Knotweed foliage and flowers were used for animal fodder and, originally prized for their beauty – so much so that the Society of Agriculture and Horticulture named it the most interesting new ornamental plant in 1847.

The interest in the plant inevitably evolved into the best ways to effectively get rid of it since it proved to be an invasive, ferocious, and destructive plant. Its natural habitat is on the side of volcanoes and its spread was limited by insects, native fungi, deposits of volcanic ash, and extreme climate, but there are no such predators or natural regulators in Britain.

What Does Japanese Knotweed Do?

what is japanese knotweed

According to Environet Japanese Knotweed is believed to cost the UK economy about £166 million annually in property devaluations and for treatment.

It rapidly spreads, wiping out the native species in its relentless progress across the land and poses a serious threat to drains and building foundations. It can grow as much as 20cm a day; its root system can go as deep as 3 meters into the ground; a single plant extends as much as 7 meters in every direction and can break through concrete and tarmac.

This plant essentially spreads like wildfire when growing and can also spread when anybody attempts to get rid of it, unless it is a professional doing it. Even a small fragment of rhizome or stem can easily take root and regrow into another ravenous plant, which makes it extremely difficult to eradicate.

The gardens of the aristocracy during Victorian times were full of exotic plants and whenever one went out of vogue or failed to thrive, it would be dug up and subsequently discarded. Japanese Knotweed was one of those plants.

Japanese Knotweed was dumped in waterways, disused quarries, or anywhere conveniently out of sight. The practice continued unknowingly made worse by the movement of contaminated soil for the construction of railways and roads along with other construction projects, until the full extent of the damage it caused became clear.

It can thrive everywhere and anywhere. It keeps on thriving, given half a chance, in spite of the recent changes in regulation that strictly regulate the disposal and transportation of roots, stems, and infected soil.

Other Information About Japanese Knotweed

Japanese Knotweed: What Does It Look Like?

It will look different depending on the time of year. The following is a brief description of how the plant looks in different seasons.

Japanese Knotweed During Spring

The first signs of growth of this plant are usually seen in mid-March. Distinctive red as well as purple shoot – usually accompanied by rolled back leaves that grow rapidly from the nutrients stored in the rhizome.

Japanese Knotweed During Summer

The stem of the Japanese Knotweed plant looks like bamboo, but a bit greener in color and has purple speckles too. Distinctive chambers can be found within the cane that are responsible for retaining nutrients and water. The leaves of the plant are also large with pointed tips extending in a zig-zag pattern from the stem during this season. Creamy-white flowers hang from the stalks in clusters later on in the season.

Japanese Knotweed During Fall

The bamboo-like stems turn darker brown and have a lot of foliage. The leaves are large and heart-shaped with pointed tips extending from the stem in a zig-zag pattern. The leaves wilt and start turning yellow.

Japanese Knotweed During Winter

The leaves of the plant will turn brown as the frosts appear and the plant withdraws back into its rhizome. The canes start losing their color and turn into woody stalks that can take several years to decompose. New shoots then start growing through the dead canes in early Spring.

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