Japanese Knot Weed

Japanese Knot Weed/Japanese Knotweed (Polygonum sp.)

This fall perennial is native to Asia, China, Japan and Korea. It is found growing worldwide and once believed to be "a plant of sterling merit" in Britain. Now it is considered Britain's most problematic weed. In the United States it is considered one of the most seriously invasive weeds in the east.

Other names include Fleeceflower and American bamboo. Bamboo because knot weed has stems that are hollow along with distinct raised nodes, giving it the same appearance of bamboo and growing up to 10 feet tall.

The large green leaves are an oval shaped with a point at the end of it. Long, loose white to cream colored flower clusters that grow upward from leaf branches. The flower clusters bloom in late summer to early fall.

It's rooting system spreads by roots and rhizomes. Rhizomes create a large underground network traveling deep into soil and several feet beyond the plant above soil surface. Because of this it will damage soil foundation.

Photo: Whiskybottle

Young fleece flower stems are considered edible, otherwise a mature weed is noxious. It will grow anywhere and on anything, including the cracks of a sidewalk. As it grows it smothers out other vegetation.

Japanese Knot Weed Roots need to be Killed!

If plants are young they can be pulled - but stems can break off easily. If this happens, dig out the root system.

Photo: Whiskybottle

With mature plants the goal is to starve the root system. Before this is done, consider how to control new growth of re-rooting - it takes years to eradicate.

First cut the plant to ground level. Stems are very difficult to cut through and it is important to avoid spreading anything that could re-sprout. Because of this it is recommended not to mow over Weed. Mulching over root system does not always work. Like bamboo, stems grow through just about anything.

Herbicides come with special considerations with regards to habitats near wet areas, as this weed is found around lakes and river beds. Outside of this, it is recommended to use a glyphosate herbacide because of it's ability to be systemic with the hard stems.

Local authorities that have dealt with this weed on a large scale appear to agree it is a combination of cutting the weed down combined with a post-emergent herbicide.

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