Japanese knotweed

Photo: Tom Heutte, USDA Forest Service, Bugwood.org 

Updated: March 19, 2021

About Japanese knotweed (Japanese bamboo)

Life cycle

Japanese knotweed (Polygonum cuspidatum) is a herbaceous perennial plant.

Growth habit

Grows up to 10 ft. high; shrubby; leaves 6 in. long by 3 in. wide, oval with smooth margins; stems similar to bamboo, but on new foliage a membranous sheath surrounds area where stem and leaf meet; flowers small green-white in spikes along the stems; small, greenish, triangular fruits

japanese knotwood patch

Photo: Barbara Tokarska-Guzik, University of Silesia, Bugwood.org 


Reproduces from heavy rhizomes primarily but does produce viable seeds.

Conditions that favor growth

Introduced as an ornamental and escaped cultivation; common weed of moist well-drained soil

Cultural control

Dig out as much root as possible and destroy; repeatedly destroy regrowth to exhaust energy reserves; this can take several seasons to get under control.