Identifying Japanese Knotweed

Japanese knotweed identification is an uphill task that involves a lot of technical know-how and understanding. The best time to identify the Japanese knotweed is in mid-summer or early autumn when their growth is rapid with the plant growing by about 2cms a day. Consequently, forming a dense covering of their stems.

Stems
Their stems are hollow and have purple speckles and the stem may grow up to 3 metres in height. Their stem is similar to that of a bamboo plant in that; its inside is hollow. Japanese knotweed stems grow to 2-3 metres tall and their growth is alternate on the stem thus producing a zigzag pattern.

The plant has distinct leaves that occur in 3 stages based on their age. New leaves are 1 to 4 cm in length and are dark red. Its young leaves are green and have red veins. At this stage, the foliage is usually rolled back. When these leaves mature up, they are green in color and have a shovel shape. They are usually about 12 cm in length.

Flowers
The plant’s flowers are small and occur in clusters. These clusters grow to a width of 0.5 cm and a length of 10 cm. They are usually creamy and white in colour and bloom in late summer. The Japanese knotweed has small winged seeds that are heart shaped but are sterile since there are no male plant species in the UK.

Rhizomes
Their rhizomes have a diameter ranging from a few millimetres to about 20mm. They can grow to a depth of about 2 metres and extend to about 7 metres in a horizontal direction. On top of this, they have a characteristic dark brown exterior with the inside being orange or yellow in colour and these rhizomes are easy to snap.

Crown buds
Its crown buds form in spring and it is from these buds that new stems grow. They are round in shape with a width of 1-3 cm. They are bright red or pink in colour.

The characteristics of japanese knotweed identification also vary from season to season. In spring, the shoots appear from the crown buds and are usually fleshy. The leaves from the buds are red or purple and are rolled up. In summer, the plant experiences rapid growth with the stems growing to a height of about 2 to 3 metres. These stems are usually green in colour with purple or red speckles. Moreover, they have nodes between sections and are hollow. The flowers also appear in late summer around the months of August and September. In autumn the plant’s flowers flourish with small seed cases falling off from the bracts of the stem. Yellowing of the leaves usually occurs beginning at leaf margins and later spreading to the whole leaf before finally falling off. The stems also redden during this season.

In winter the leaves fall off and the plant’s shoot die off leaving dead stalks that are hollow and are similar to bamboo stems. In scenarios where a mild autumn with no frosts is experienced, the plant’s shoots may persist or new shoots may emerge.

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