Common Knotweed


No matter what you do, sometimes weeds seem impossible to prevent. The common knotweed has unfortunately developed the ability to thrive in compacted soil, and this plant will often spring up in areas where plant growth looks unattractive, such as between the cracks of sidewalks. This weed isn't difficult to prevent or kill, but the weed is often confused with other plants.


The scientific name given to common knotweed is Polygonum arenastrum. Common lnotweed is also called wiregrass, wireweed, matweed and doorweed. The common knotweed has wiry stems and often grows along the ground, creating wiry mats. In very good conditions, this plant can grow erect. The leaves of the common knotweed are bluish-green and has blades that are narrowly ovate. Leaf stock is very short, with leaf stipules surrounding stem nodes. Since these nodes look like knots due to their swollenness, this plant received the name "knotwood." The common knotweed develops flowers that are small and hard to notice, with white or green colors and a slight pink tone. The common knotweed produces a fruit that is dark brown and dull. Some variations of the knotweed grow more erect, like the silver-sheathed knotweed, growing 12 to 20 inches tall.


The common knotweed came from Europe and has since grown throughout the United States and Canada. This hardy weed also appears along paths and walkways because it has evolved to become tolerant to compact soil.

Time Frame

Common knotweed is an annual. The common knotweed germinates early in the spring. The plant survives well in areas where there is summer drought, since the weed is adept at collecting spring rainfall. During that time, the common knotweed develops a taproot, which can penetrate as deep as 18 inches. The common knotweed often becomes prostrate, which means that it can develop into a mound that spreads across the ground and grows to a height of 4 inches.


The common knotweed grows among field crops, row crops, orchards, yards, gardens and turfs, where the weed saps nutrients and water away from other plants. The common knotweed is often confused with the spotted spurge. The best way to distinguish the common knotweed from the spotted spurge is to break a stem of the plant and see if milky-white sap oozes out.


Unlike most plants that do not like compacted soil, the common knotweed thrives in it. Unpacking soil can discourage the common knotweed from growing. Try to spread out the movement of people and machinery over a given area so the soil does not become too compacted. Mulches also prevent knotweed. When common knotweed starts springing up, you can remove them with weeding tools like the swivel hoe or with herbicide.

Keywords: common knotweed, hardy weed, compact soil

About this Author

Charles Pearson has written as a freelancer for two years. He has a B.S. in Literature from Purdue University Calumet and is currently working on his M.A. He has written three ebooks so far: Karate You Can Teach Your Kids, Macadamia Growing Handout and The Raw Food Diet.