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Polygonum, Genus, aviculare, Species,

Genus & species

common knotweed

Europe and western Asia; compacted paths, driveways, farmyards, roadsides, and waste ground from sea level to approximately 10,000 feet (3,000 m).

Deer Resistant Drought Tolerant

SunFull Sun

WaterLow · drought-tolerant

Overview

Polygonum aviculare is a prostrate wiry annual reaching 2-8 inches (5-20 cm) tall and 12-48 inches (30-120 cm) wide, forming flat mat-like colonies on compacted surfaces. Stems are prostrate, much-branched, wiry, tough, with swollen nodes and silvery papery tubular sheaths (ocreae) at each node, the Polygonaceae family-level identification feature. Leaves are alternate, elliptic to lance-shaped, 0.4-1.2 inches (10-30 mm) long, blue-green to gray-green, and progressively smaller toward the stem tips (heterophylly, a leaf-size gradient along the stem). Tiny greenish-white to pinkish flowers open singly or in clusters of 1-5 in the leaf axils, each with 5 tepals. Fruit is a dark brown trigonous (three-angled) achene 0.08-0.12 inch (2-3 mm) long with a dull (not shiny) surface. A single plant produces 500-6,000 seeds that remain viable in soil beyond 20 years. The species thrives on compacted heavily trafficked surfaces and is common on gravel driveways, sidewalk edges, field entrances, barn lots, and paths, a habitat preference shared with Matricaria discoidea (pineapple weed) and Plantago major as the three main soil-compaction indicator species of temperate paths.

Native Range

Polygonum aviculare is native to Europe and western Asia, where it grows on compacted paths, driveways, farmyards, roadsides, and waste ground from sea level to approximately 10,000 feet (3,000 m). The species has naturalized across all 50 U.S. states and all Canadian provinces and is a cosmopolitan weed of compacted high-traffic surfaces worldwide.

Suggested Uses

The species is used in Polygonaceae identification courses for teaching ocrea structure and heterophylly (leaf-size variation along a stem). Dominance on a site is used as a soil-compaction indicator alongside Matricaria discoidea and Plantago major in land-management assessment. The long-lived soil seed bank, with viable seeds documented beyond 20 years, is a teaching example in weed seed biology. Seeds are consumed by ground-feeding birds and the species is studied in urban wildlife ecology; foliage has a long historical record of use as a famine food in several European and Asian cultures.

How to Identify

A prostrate wiry annual 2-8 inches (5-20 cm) tall forming flat mats of much-branched wiry stems carrying silvery papery ocreae at each swollen node. Leaves are alternate, elliptic to lance-shaped, 0.4-1.2 inches (10-30 mm) long, blue-green to gray-green, progressively smaller toward the stem tips (heterophylly). Tiny greenish-white to pinkish flowers 5-tepaled open singly or in clusters of 1-5 in the leaf axils. The prostrate wiry mat-forming habit with silvery ocreae at swollen nodes and the progressively smaller leaves toward stem tips separate P. aviculare from Persicaria smartweeds (which have erect habits and dense spike-like racemes rather than axillary flowers), and from Portulaca oleracea (purslane, which has succulent stems and opposite-to-sub-opposite leaves and no ocreae). The extreme tolerance of compacted trafficked surfaces is itself a habitat-level identification character. Achenes are dull rather than shiny under a hand lens.

Appearance

Size & Dimensions

Height2" - 8"

Width/Spread1' - 4'

Colors

Flower Colors

Foliage Colors

Fall Foliage Colors

Bloom Information

Bloom Period

~12 weeks

Flowers: June–October

Summer Fall

Tiny 5-tepaled greenish-white-to-pinkish flowers open continuously in the leaf axils as stems elongate from June through October, with a total bloom span of 10-14 weeks in the Pacific Northwest. Flowers are self-pollinating. Seeds mature progressively from the base of the stem outward toward the tips, and in the Pacific Northwest flowering runs from late spring through the first hard fall frost.

Detailed Descriptions

Flower Description

Greenish-white to pinkish; tiny flowers carried singly or in clusters of 1-5 in the leaf axils, with 5 tepals each

Foliage Description

Blue-green to gray-green; elliptic to lance-shaped, alternate, 0.4-1.2 inches (10-30 mm) long, progressively smaller toward the stem tips (heterophylly); each stem node carries a silvery papery tubular sheath (ocrea) that is the Polygonaceae family identification feature

Growing Conditions

Sun Requirements

SunFull Sun

Requires 6-12 hours of direct sunlight daily

• Full Sun: 6+ hours of direct sunlight

• Partial Shade: 3-6 hours of direct sunlight

• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range5.0 - 8.5 (Acidic to alkaline)

3579

Soil Types

loam sand silt clay rocky

Drainagewell drained

Water & Climate

Water Needs

Low

Frost Tolerance

hardy

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Hand-pulling is possible but the wiry stems are tough and resist pulling; a sharp hoe used to sever the plant at the root crown is more efficient for large mats. The annual life cycle means plants do not persist from roots, but the soil seed bank that remains viable beyond 20 years means reduction from established sites requires sustained management over many years rather than a single growing season. Reducing soil compaction by aerating, adding organic matter, and establishing competitive ground covers shifts the competitive balance away from knotweed. In gravel areas, improving drainage and maintaining a clean gravel surface reduces establishment; in garden beds, dense turf or mulch prevents germination.

Pruning

No pruning is applicable. Plants are pulled or hoed before seed maturity. The wiry stems resist hand-pulling, and a sharp hoe gives faster removal for large mats. The annual habit means complete removal prevents regrowth from the pulled root system.