Japanese Knotweed is a perennial plant of the family Polygonacae. Its latin name is Polygonum cuspidatum. It has been known also as Japanese Bamboo, Mexican Bamboo, Fleece-Flower, and Hancock's Curse.

Identification and Stats:

The plants themselves have hollow green stalks and thick green leaves. The stalks are jointed and very weak (they can be knocked over with something as light as a hockey stick). Early in the year they will appear as small red shoots which gradually turn green as they rise. Late in the summer they produce white flowers. The female flowers will produce a small black berry if there are males present. When they die in the fall, they don't fall over, but turn very woody and remain standing.

It grows to a height of 1 to 3 meters very rapidly, and can grow up to 45 centimeters in a 24 hour period. Growth occurs primarily during the night, from energy stored up during the day. The root system can extend up to 20 meters laterally and down to a depth of 2 meters. The plant is capable of fully regenerating from a piece of root as small as 0.7 grams. The plant seems to require lots of water, and grows most rapidly near waterways.

Because of the density of the stalks and the number of leaves produced by this plant, they quickly exclude all other species from growing in an area where they have taken over. The leaves themselves, when decomposing, are highly acidic and rich in tannins, and will prevent most plants from growing.

In China, the shoots and leaves have traditionally been eaten. The shoots taste much like rhubarb and can be cooked in the same way (covered with sugar and simmered). It has been used medicinally for thousands of years. It acts as a laxative and has been used to help treat and prevent ulcers.

The Problem:

Japanese Knotweed was introduced to England in 1825, and North America some time in the 1800s as a decorative plant and erosion control mechanism. Without its natural enemies it quickly became uncontrollable and took over wherever it was planted. The system of plants invading England are actually descended from only one plant (they are clones of one another).

No chemical solution is truly effective at subduing this plant. It will nearly always grow back, since it is capable of regenerating completely from the root. The most promising solution appears to be biological control, by introducing one of the 30 insect species or 6 fungus species that feed on the plant.

Whenever the plant is completely removed or destroyed with chemicals, the remaining "scorched earth" will be a problem for erosion, particularly on the banks of rivers. The decaying acidic leaves and stalks will prevent the ground from being usable for some time.

  • http://www.explore-gower.co.uk/swanseacity/jknotweed.htm
  • http://www.cabi-bioscience.org/html/japanese_knotweed_alliance.htm
  • http://www.ecy.wa.gov/programs/wq/plants/weeds/aqua015.html
  • http://infoweb.magi.com/~ehaber/factbamb.html
  • http://www.wildmanstevebrill.com/Plants.Folder/Knotweed.html