Prostrate Knotweed
Broadleaf weed
Prostrate knotweed (Polygonum aviculare) is a low, mat-forming summer annual broadleaf weed found across the United States. Gardeners and growers notice it because it is one of the first weeds to sprout each spring and because it thrives in the hard, compacted ground where most other plants struggle, making it a common sight in worn lawns, along walkways, and in driveways.
How to identify it
It grows flat against the soil, forming a dense circular mat that can spread a foot or two wide from a single central taproot. The stems are wiry, tough, and highly branched, with a small papery sheath (ocrea) wrapping each swollen joint or node. Leaves are small, narrow to oval, and blue-green, attaching alternately along the stems. Tiny greenish-white to pinkish flowers form in the leaf axils and are easy to overlook.
Where it grows
Prostrate knotweed favors compacted, low-oxygen soils and disturbed ground, so it shows up in thin lawns, garden edges, paths, sidewalk cracks, driveways, parking areas, and along fence lines and field margins. It germinates very early, often in late winter or very early spring before soils warm for most weeds, then grows through the summer and sets seed before frost. It spreads entirely by seed, which can persist in the soil for years.
Why it is a problem
In turf and gardens it competes with desirable plants for space, water, and nutrients, and its dense mats can smother thin grass and young seedlings. Because it tolerates foot traffic and compaction so well, a heavy stand is usually a sign of an underlying soil problem that will keep favoring the weed. It is not considered toxic, but its tough, wiry mats are difficult to mow cleanly and detract from lawn and bed appearance.
How to manage it
The most effective long-term fix is relieving the soil compaction that gives knotweed its advantage, using core aeration and by reducing repeated traffic over the same ground. Build a thick, competitive stand of turf or a healthy garden bed, and cover bare soil with mulch so seeds have no open ground to colonize. Hand pull or hoe young plants while they are small and before they set seed, aiming to remove the central taproot; a mat is easiest to lift after watering or rain. Because seeds sprout so early, scout and act in late winter and early spring, and keep after new plants each season to draw down the seed bank.
Commonly confused with
It is most often confused with prostrate and spotted spurge, which ooze a milky sap when broken while knotweed does not, and with prostrate pigweed; the papery sheath at each stem node is the reliable clue for knotweed.
General guidance for US lawns and gardens, focused on prevention and non-chemical control. For a confirmed identification and options specific to your area, contact your local Cooperative Extension office. Page updated Aug 4, 2026.