Pests & Diseases

How to Properly Identify Japanese Knotweed?


Japanese knotweed is a hardy and invasive shrub that has been spreading rapidly over vacant lots and pastures across the land.

Because of its dense foliage, Japanese knotweed is often mistaken for dogwood or other shrubs common to the area. But Japanese knotweed can be best identified by its creamy white flowers that it produces in great abundance during the late summer. It also features segmented bamboo-like stems and large shovel-shaped leaves. You can learn more on Environetuk.

If you have a great green monster sprouting up on your property, a better understanding of your visitor is the best way to begin. Here are some of the characteristics of the invasive Japanese Knotweed:

Japanese knotweed (Reynoutria japonica)

Japanese Knotweed Flowers – blossoms of cream white, 0.5cm wide, form in tall clusters that can grow to 10cm. Blooms in the very late summer, typically between August and September.

Japanese Knotweed Leaves – the shovel-shaped leaves are light green but can contain flecks of red and purple. Leaves can grow a full 20cm (about 7.87 in) and shoot off from nodes in a zig-zag pattern. New leaves will begin in rolls with red veins.

Japanese Knotweed Stem – structured in a zig-zag formation, the stems of the Japanese knotweed are also green with flecks of red and purple. They are hollow and can grow as much as 2-3 meters in height. This fast-growing weed can grow as much as 2cm in a day.

Japanese Knotweed Height – Typically grows to a height of 2.1m (7ft) but has been known to grow higher than 3m (9.8ft).

Japanese Knotweed Growth Rate – Can grow a full 10cm (about 3.94 in) per day during late spring / early summer.

Japanese Knotweed Seeds – heart-shaped seeds featuring small wings. Seeds rarely germinate, new plants are spread from rhizomes deep in the ground which can extend for great distances.

Japanese Knotweed Origin – Native to Japan, and parts of Korea and Taiwan.

The topic of Japanese Knotweed has been discussed and debated from the halls of Parliament to the property divisions where neighbors fear the marauding Phyto-menace. Identification of this weed is needed before legal action can be taken. While it is quite possible to make an identification from the description mentioned above, the plant can take on many different forms at different times of the year. If you know what to look for a positive identification can be made at any time of the year.

The point of this short writ is to point property owners in the direction of getting proper help when identifying this plant and to understand how the plant can change throughout the year. We also point out that this plant can be mistaken for other plants as well and that there are risk factors related to infestation.

Japanese Knotweed Identification

As experts in all things related to knotweed, we can provide accredited Japanese Knotweed identification through a variety of identification methods. If you suspect that this fearsome weed is growing unchecked on your property and would like a proper identification of the problem, we are here for you. Just fill out the contact form on the side of the page and include some images of the plant in question so we know what we are looking at.

Knotweed shoots grow to around 2-4m and grow 2cm a day.

Knotweed has nodes between stems, like bamboo.

Knotweed leaves grow in zig-zag patterns.

Japanese knotweed leaves are green, shovel-shaped, and have a pointed tip.

Knotweed flowers bloom at the start of August and have been known to continue blooming late into September.

The plants emerge from dense clumps.

Japanese Knotweed grows up to around 2.1m (7 feet) in height.

How do I know if I have Japanese knotweed?

It can be difficult to get a positive identification if you are not familiar with this plant or how it can change throughout the year. There are also many local plants that can be mistaken for invasive Japanese Knotweed.

If you believe you have a Japanese Knotweed infestation on your property, it is a good idea to give the experts a call right away. Japanese knotweed can cause damage to the environment and affect the value of your property. If you bought the property with an infestation already present, or if your Japanese knotweed crept over from a neighboring property, we can help you find financial support to address this issue.

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