Giant knotweed

(Fallopia sachalinensis)

Giant knotweed is a native of South Sakhalin, Honshu (in the north of Japan), Korea, and the Kurile Islands. It is a closely related species to Fallopia japonica, but less widely distributed outside of the Far East. Both male and female plants have been recorded in Europe and the UK. Although similar in many respects to japonica (cane structure, distinctive ‘zig-zag’ shape of stems, similar growth habit, etc), it grows much taller (4-5 metres or 13-16 feet) and has much larger, elongated leaves. The leaves can grow to around 40cm (16 inches) long and up to 27cm (11 inches) wide.

They are pointed at the tip, somewhat crinkly in appearance and have long white hairs (trichomes) on the underside. The base of the leaves are deeply lobed, forming a heart shape. Growth generally begins later than japonica, usually mid to late spring, and leaf drop generally occurs earlier than japonica in the autumn. Rhizomes are more creamy in colour internally, rather than the distinctive orange of japonica. Creamy-white flowers appear in late summer/early autumn in dense panicles hanging off the stems. The Japanese call Giant knotweed ‘o itadori’, which, with enviable simplicity, means “big strong plant”.

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