Identifying Japanese Knotweed

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Japanese knotweed can be hard to identify in your garden because it’s often mistaken for a harmless plant or goes unnoticed by the untrained eye. However, if an infestation is left to run rampant or grows too close to a property of infrastructure, it can cause severe and costly damage, making it one of the UK’s most dangerous plants.

The best way to avoid a Japanese Knotweed infestation is to remove the plant in its early stages and have it dealt with by professionals.

How to identify Japanese Knotweed?

The most noticeable feature of Japanese knotweed is its heart-shaped or shovel-shaped leaves. Depending on the time of year, the plant’s appearance changes, making correct identification even more difficult. The shoots of Knotweed have a reddish-purple hue when they first start to grow, and light green leaves develop fairly early on.

In summer, the stems may start to resemble bamboo shoots and will develop purple specks. The leaves will grow larger and have distinctive ribs and veins. Late in the growing season, you may see small, cream-coloured flowers developing. These flowers are formed of dense clusters of small flowers on thin spikes around 10cm long

As autumn progresses, the leaves will turn yellow and slowly wilt. The stems then turn brown, and the plant enters its dormant winter stage. Throughout the Autumn to Winter transitional period, Japanese Knotweed still has the tremendous power to grow up to 3 metres.

Images of Japanese Knotweed

What other plants look like Japanese Knotweed?

Many plants are often mistaken for Japanese knotweed, including the Himalayan balsam plant, bindweed, broadleaf dock, Russian vine and some lilac shrubs.

For example, the leaves of bindweed are heart-shaped, making them look similar to Japanese knotweed. One distinguishing factor is that bindweed is a climbing plant, hence it tends to wrap itself around structures and walls in the garden.

Due to the difficulty of identifying Japanese knotweed and the benefits of early detection, it’s recommended to seek professional assistance if you suspect you have this invasive plant in the form of a survey. In most cases, a survey will be completed to determine the presence or absence of the plant over an area of land. Once the survey has been completed, you’ll receive confirmation or deny the presence of the invasive perennial plant, along with a recommended plan of action.

Where does Japanese Knotweed grow?

Japanese knotweed thrives in a diverse range of growing conditions and soil types. Its rapid growth rate makes it one of the most troublesome and invasive plants in the United Kingdom.

If allowed to spread freely and given suitable growing conditions, Japanese Knotweed can quickly invade large areas. Capable of growing up to 3m in height and spanning several metres underground from the plants visible source, the rhizome systems help to rapidly increase the rate at which Japanese Knotweed can be seen sprouting above ground.

Sites such as railway lines, derelict construction sites, and waterways are popular habitats for the plant, where the spready often left largely uncontrolled.

How do I remove Japanese Knotweed?

Due to the plant’s invasive nature, self-treatment or removal without the proper equipment is not recommended. In fact, it is illegal in the United Kingdom to spread Japanese knotweed onto other land, so attempting to remove it yourself could land you in trouble.

The few safe disposal methods available include incinerating, disposal at an approved facility, and burial beneath a protective membrane, but they are not feasible for most hobbyist gardeners. 


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