How To Identify Japanese Knotweed

It is not easy to identify Japanese knotweed. You need to know the key features. It is the most widespread form of knotweed. A zigzag stem growth pattern is a distinct Japanese knotweed identification. A growth pattern of They could be destructive if you ignore a potential infestation.

When to look for Japanese knotweed? 

The best time is during mid-summer and early autumn. Reddish or purple shoots appear from the ground during spring. These shoots look like fat asparagus and they lengthen from bright pink buds at a rapid rate. They sometimes grow up to 2 centimeters a day. Dense stands of stems that look like bamboo form fast. It develops green leaves that are heart-shaped or shield-shaped.

The mature Japanese knotweed stems are hollow by early summer. They have purple speckles and can reach up to 3 meters high. Leaves produce an obvious zigzag pattern by alternating along each side of the stem.

Creamy white flowers show up by late summer. These appear in a lengthy cluster or spike formations. Japanese knotweed’s roots or underground rhizomes lie dormant over the winter months. It starts to sprout and bloom once the winter is over.  Its rhizomes can spread meters from the visible stems. It is easy to spread them by disturbing the soil a few meters from where the stems appear.  New growth from seeds is very rare. It only proves its incredible invasiveness. It spreads over the world by the fragmentation and translocation of contaminated soil.

japanese knotweed identification

What do Japanese knotweed leaves look like? 

New leaves of Japanese knotweed are dark red. They are about 1 to 4 centimeter long. Young leaves are dark green. It is often rolled up with dark red veins. Mature leaves are green with the shape of a shield. These are usually around 12 centimeters long.

What do Japanese knotweed stems look like? 

Mature stems are about 2 to 3 meters tall. Japanese knotweed stems look like bamboo with obvious rings and purple speckles. You can see a zigzag pattern at the top because of leaves shooting in the opposite directions. Mature stems are not at all woody. You can snap the stems with no effort since they are so hollow.

What do Japanese knotweed flowers look like? 

These bloom in late summer. Japanese knotweed flowers are creamy-white and about 0.5 centimeters wide. They form clustered spikes of flowers amongst the foliage. The spike lengths are about 10 centimeters.

What do Japanese knotweed rhizome or root look like? 

The exterior of the Japanese knotweed rhizome is dark brown. The interior is orange or yellow or a little of both. The roots are easy to snap like a carrot. Sections of the root can be from a few millimeters to 20 centimeters in diameter.

A very important distinction is that it does not reproduce by seeds. It is only possible with pieces of stem and rhizome. Hybrid seeds are also produced by Japanese knotweed. These seeds very rarely develop into viable plants so do not fret.

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About the Author: Jacob Wyatt