Japanese Knotweed Identification
Japanese knotweed is a highly invasive perennial plant which causes severe harm to thousands of properties and grounds each year in the UK. Fortunately, the Japanese Knotweed identification process is relatively easy. However, without the correct professional treatment or control, the Japanese weed can cause significant damage.
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Japanese knotweed, or given its scientific names Fallopia Japonica, Reynoutria Japonica and Polygonum Cuspidatum, belongs in the same family as rhubarb, sorrel and buckwheat. Some other common names for the weed includes donkey rhubarb, elephant ears, Japanese bamboo, American bamboo, Monkeyweed and fleeceflower.
Origins In Asia
The Japanese weed is originally from Korea, Japan and China where it was discovered in the late 18th century. Brought from Asia to Europe, it was imported into the UK during the middle of the 19th century.
There are many myths about the introduction of Japanese Knotweed into the UK. They range from being introduced by the Victorians as a decorative plant, cheap feed for cattle and being used as a method of anchoring sand dunes. It was even used to support the soil levees on canal and railway embankments by using the plant’s extensive root system.
By the early 20th century, the full impact that Japanese Knotweed was having in areas where it was planted was being realised. In the absence of any natural insect or animal predators, in addition to no fungi or diseases, the plant has thrived in the UK conditions. Consequently, the weed has spread quickly, particularly along railway lines, canals and rivers. It is likely that on average there is a stand of Japanese Knotweed in every 10 square kilometres throughout the UK.
What Does Japanese Knotweed Look Like?
So what does Japanese Knotweed look like? The plant is known as a herbaceous perennial. Although Japanese Knotweed identification is simple, there are still many plants mistaken for Japanese Knotweed. The identification process changes during the seasons. This can make it quite challenging. Explore our seasonal Japanese Knotweed identification guide for more information on the Japanese weed below.
Spring is when the Japanese weed shows first signs of growth. The small, reddish purple asparagus like shoots, with bright green wrap around leaves, start emerging from the ground. The leaves begin to unfold in a heart, or shield shape, with a smooth upper surface and reddish veins underneath. This makes leaf identification one of the main defining characteristics. The Japanese Knotweed shoots are hollow, but very strong. This allows the plant to rapidly grow up to a height of 2 – 3 metres in a single season.
Eventually, mature plants can have leaves up to 10 inches long and green stems with reddish spots that can grow up to 50 mm in width. Additionally, the leaf shoots appear on alternate sides along the entire main stem. The main stem has a bamboo like appearance which creates a large, shaded leaf canopy. This makes it almost impossible for other plants to grow underneath.
During the summer months, the weed grows most agressively. This makes Japanese Knotweed identification easiest, but also provides the most challenging conditions for treatment. Japanese knotweed shoots will continue to appear throughout the growing season, producing colonies with copious leaf canopies.
By late August, clusters of creamy white flowers appear that produce seeds. These seeds are currently sterile and unable to produce new plants. Therefore, concern about the plant spreading through seed transfer is unsupported. All Japanese Knotweed plants currently in the UK are female. Consequently, the only way that Japanese knotweed can spread by small pieces of its rhizome, or root system. This method is very efficient, which allows the plant to spread vigorously.
Autumn & Winter
When autumn arrives, the Japanese Knotweed identification is still rather easy. The leaves gradually turn brown, eventually falling to form a thick layer of slowly decomposing mulch. As a result, this leaf mulch prevents many native seeds from germinating.
As winter approaches however, the plant withdraws all nutrients and moisture from the leaves and stem back into the rhizome. The stems form unsightly brown, hollow bamboo like brittle canes that decompose very slowly. The crown, rhizome and roots remain dormant throughout the winter easily surviving frozen conditions.
The dormant stage of the life cycle is the most challenging of the Japanese Knotweed identification. The weed appears to have been eradicated, when in fact it has been laying low. Without the expert knowledge of our professionally trained team, the weed can spread even further when spring and summer return.
Rhizome Root System
Whilst the development of the plant above ground is impressive, the spread of the rhizome root system below the soil surface is even more so. The rhizome of a small stand (colony of a few stems) of Japanese Knotweed can produce over 200 new shoots. Some appearing as far as 7 metres away from the parent plant, emerging from deep in the soil. The new stands form dense thickets which remain connected to the parent, allowing all plants to share the energy contained in the rhizome system.
This sharing of energy provides the new emerging shoots with enough power to break through tarmac, concrete and even break through joints in brickwork and pipes. New plants can emerge from a piece of rhizome as small as 2 cm. Fresh stems can also produce new shots and roots when buried. Japanese knotweed thrives where there is available water such as streams or damp areas with plenty of sunlight. Poor soil conditions do not prevent Knotweed developing. Japanese Knotweed can withstand heavy clay or sandy soils and a wide range of acidic and alkaline conditions.
Plants That Look Like Japanese Knotweed
There are several species of plants that look like Japanese Knotweed. As an invasive perennial weed, Japanese Knotweed shares many characteristics with other aggressive plants. These include Japanese Bindweed, Russian Vine, Bamboo, Broadleaf Dock and Ground Elder. However, if you have trouble identifying Japanese Knotweed, do not worry! Our qualified and experienced team are here to help with our FREE survey.
Invasive Perennial Weeds
Japanese Knotweed shoots are very tolerant to regular strimming, cutting and extremes of temperature. It will even survive burning, with stems emerging a few days after the stand has burnt down. Do not spread cuttings around. It is classified as controlled waste and therefore needs to be handled and disposed of to a licensed site that accepts controlled waste. Consequently, ignoring these rules, or fly tipping knotweed waste can lead to prosecution and heavy fines. The simple act of cutting or disturbing the soil around the plant if not strictly managed could be classed as encouraging the Knotweed to grow. In many cases well intentioned cutting of Knotweed is the reason it has spread.
Disturbing the ground encourages the plant and stimulates rhizome activity. The rhizome appears as a brown knotted root and is a bright orange colour inside. The roots have the snapping characteristic similar to a carrot when broken. The rhizome sends down hundreds of fine white roots into the soil.
This destructive power to locate and exploit weaknesses in structures damages buildings, surfaces and its ability to spread to the detriment of all other flora and by consequence fauna makes Japanese Knotweed a formidable plant. Large areas of land continue to be colonised by Japanese Knotweed forcing natural flora and fauna out and producing serious environmental and commercial consequences.
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Have any questions about our identification guide? Want to request a FREE survey? Simply contact us with as much detail as possible about the extent of the contamination and growth.