Common Knotgrass (Polygonum aviculare)

Common Knotgrass

Polygonum aviculare

It spreads low and tough, a quiet ground cover for sunny wastelands. Short-lived perennial or annual herb; common names: doorweed.

Full sun
1–2/week
Beginner
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Plant Needs

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Sunlight Thrives in full sun; tolerates partial shade and compacted, low-nutrient soils
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Watering Drought-tolerant; water only during prolonged dry spells to avoid root rot in poorly drained soils
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Temperature Hardy to frost and cold temperatures; tolerates summer heat in temperate and Mediterranean climates
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Characteristics

  • Leaf: Small linear to oblong, 5–20 mm long, blue-green, alternate arrangement
  • Flower: Tiny white to pale pink blooms clustered in leaf axils, 2–3 mm across
  • Stem: Slender reddish-brown stems forming dense, low-growing mats
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Care Guide

Watering

Water sparingly during extended dry periods; avoid overwatering

Fertilization

Optional diluted feed once monthly if growing in very poor soil. Avoid heavy fertilization to prevent excessive, leggy growth

Composted eggshell powder:Sprinkle a thin layer on soil surface; mix lightly into topsoil to boost soil structure and nutrient availability
Pruning
  • Trim overgrown mats in early spring to maintain a compact, neat form
  • Remove dead foliage in autumn to reduce fungal disease risk
  • Thin dense clusters to improve airflow in humid summer conditions
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Toxicity

Warning: this plant may be toxic.

Pets & Humans

Pets: ASPCA: No documented toxicity to cats

Humans: Large ingestion may cause mild gastrointestinal upset; small quantities are edible in some culinary and folk medicine contexts

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Garden Uses & Culture

Culture: N/A

Usage: Erosion control ground cover; traditional folk medicine for urinary tract support