Polygonum arenastrum
Polygonum arenastrum · Polygonaceae
The gardener's calendar
Ideal time to plant polygonum arenastrum: set it out when the soil is neither frozen nor waterlogged, and water generously as it establishes.
ID card
- Common name
- Knotgrass, Doorweed
- Family
- Polygonaceae
- Plant type
- Annual or short-lived perennial herb
- Adult size
- 10 to 40 cm in height
- Flowering
- July to October
- Foliage
- Deciduous, alternate linear leaves
- Growth
- Fast
- Hardiness
- Hardy, cosmopolitan
- Origin
- Cosmopolitan, temperate and subtropical regions
Care
Light exposure
Place knotgrass in full sun or partial shade. It appreciates bright spaces but also tolerates partially shaded areas. Avoid dense shade, which would slow its growth.
Soil and terrain type
This plant is very hardy and grows in poor, sandy or rocky soils. It adapts to difficult terrain and requires little fertility. Well-drained soil is recommended to prevent root suffocation.
Watering
Water moderately during active growth periods, especially during dry spells. Knotgrass is drought-tolerant once established. Avoid excess water, which could encourage fungal diseases.
Pruning and trimming
Pruning is generally not necessary. You can cut it back lightly in late summer to encourage a more compact shape. Remove dead or damaged parts in spring.
Fertilizer
Knotgrass is undemanding in nutrients and doesn't require regular fertilizer applications. A light application in spring is sufficient if the soil is very depleted.
Diseases and pests
This plant is generally very resistant to diseases and pests. Watch out for root rot in case of excessive moisture. No major problems reported under temperate climates.
Did you know?
Knotgrass is such a discreet cosmopolitan species that it often goes unnoticed in pavement cracks and degraded areas. Despite its scrawny appearance, it plays an important ecological role by colonizing poor spaces and stabilizing eroded soils, particularly appreciated in ecological restoration of urban wastelands.
Where to buy it
Plant in spring or early autumn, avoiding spells of intense heat. Pick a plant with healthy foliage and roots that are not exposed. Best time: March, April, May, September.
Add this plant to my garden →Plants from the same family
- SorrelRumex acetosa
- Pink knotweedPersicaria capitata
- Mile-a-minute vineFallopia baldschuanica
- RhubarbRheum rhabarbarum
- Maidenhair vineMuehlenbeckia complexa
- Red bistortBistorta amplexicaulis
Tips generated and checked by Viridia — adapt them to your local climate.