Japanese knotweed Identification | How to Identify Japanese Knotweed?

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Japanese Knotweed Identification

The first rule of Japanese knotweed elimination is to be able to recognise whether or not you have it present and active in your location. Flagging up the problem correctly is the starting point in any war raged on the notoriously territory-grasping weed, a real villain of modern horticultural times. The danger of Japanese knotweed to Britain’s homes and wildlife is clear and ever-present, but successful Japanese knotweed identification paves the way to effectively tackling the problem and ultimately defeating the enemy within many of our gardens and countryside. 

This is where we come in. Essentially, the Japanese knotweed identification process involves literally getting to the root of the potential problem, starting by establishing whether the unidentified flora object is the nasty knotweed or not. The identification process is performed by trained professionals carefully combing the location in search of the plant’s large green oval-shaped leaves and bamboo-type stem. 

That said, the Japanese knotweed is nothing if not a master of disguise, with Japanese knotweed flowers taking on somewhat differing guises and characteristics throughout the calendar year, which certainly keeps us on our toes as we set about making a positive identification. This is why the process of how to identify Japanese knotweed needs to be handled by professionals like us, experts who know what we’re talking about. Once confirmed, we can help advise you on potential Japanese knotweed removal costs.

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How To Identify Japanese Knotweed?

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Japanese Knotweed Leaves

So what do the leaves look like on a Japanese knotweed plant? Japanese knotweed leaves are bright green and heart-shaped with a smooth, rounded edge, flattened base and pointed tip. The leaves grow from the plant’s stems in an alternating pattern that gives Japanese knotweed branches their distinctive “zig-zag” shape. The leaves generally have pronounced veins and mid-rib, and have a deep red or pink coloured stalk. 

The leaves of mature Japanese knotweed plants can grow up to 120mm in length, but other species of Knotweed can grow similar leaves at sizes up to 400mm long. 

Early leaf growth in spring can be a deep red colour or light green (sometimes with red spots) but once the leaves have fully opened – often after only a few days of growth – they take on a distinctive bright green shade which they keep until the leaves die back later in the year. 

During late autumn or winter, it is common that with Japanese knotweed flowers, the leaves die back. It is important that as you consider how to identify Japanese knotweed, you’re aware that these leaves don’t re-grow from the same stems the next year, but instead form new stems every spring. 

Identify

  • Young Leaves

    Deep red colour or light green (sometimes with red spots) but once the leaves have fully opened – often after only a few days of growth.

  • Mature leaves

    Bright green in colour, the leaves of the mature plant are up to 120mm in length with a flattened base and pointed tip. Leaves and stems have developed a zig-zag pattern.

Japanese Knotweed Flowers

Does a Japanese knotweed plant have flowers? In high summer, Japanese knotweed plants develop many small clusters of creamy-white flowers. Each knotweed plant can have dozens of clusters, each of which is made up of many small flowers. The clusters of flowers grow from the point where the leaf joins the stem (the axil). The Japanese knotweed flowers can look white or pale yellow from a distance, and give the plants a very distinctive and attractive appearance at this time of year. 

Generally, Japanese knotweed plants do not produce viable seeds in the UK – although it is possible for Japanese knotweed to cross-breed with other plants, including other knotweed species. You should still avoid spreading any seeds produced by a Japanese knotweed plant, as Japanese knotweed flowers can grow from the smallest seeds and or scraps of root. 

Identify

  • The clusters of flowers grow from the point where the leaf joins the stem

  • In summer, each plant can have dozens of clusters of creamy white flowers.

Japanese Knotweed Roots

What are the roots like on a Japanese knotweed plant? The underground “roots” of Japanese knotweed are made up of a tree-like structure used to store the plant’s energy reserves. This structure is called a “rhizome”, and grows thick and woody, actually building up in rings, like a tree. Live rhizomes can be snapped like a carrot, and will show a light orange colour inside. 

It is the rhizome which causes the greatest problems related to Japanese knotweed. Structures including walls, pavements, hard surfaces and even building foundations can be displaced or damaged by the rhizomes, and the “crowns” – which are large round growths that form at the base of the stems over many years of growth. 

Japanese knotweed rhizomes can grow up to three metres deep and extend up to seven metres sideways from the surface growth. Japanese knotweed rhizomes can re-grow into new plants, even from very tiny fragments. It has been documented that a piece as small as 10mm in length, or 0.7g of rhizome can successfully grow into a new plant. 

If you are identifying Japanese knotweed by samples of root, it is important to make sure that you leave any samples in the areas that you find them, and that you don’t spread any plant material to other areas. We can inform you not just on how to identify knotweed, but also on how to kill Japanese knotweed and selecting the ideal removal method/s. 

Identify

  • The root system can grow up to three metres deep and extend up to seven metres sideways from the surface growth.

  • Rhizome grows thick and woody. Live rhizomes can be snapped like a carrot, and will show a light orange colour inside.

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