Common knapweed Centaurea nigra
Common knapweed (Centaurea nigra) is a deciduous perennial flowering plant in the Asteraceae family, native to Western and central Europe (meadows, road verges). It grows 40–90 cm (16–35 in) tall and 30–50 cm (12–20 in) wide, wants full sun and low water, and is hardy to about -30 °C (-22 °F). Space plants about 40 cm (16 in) apart.
Plan Common knapweed in your garden →
Free. Draw your beds, then watch it grow through the year in 2D and 3D.
Common knapweed at a glance
| Type | Perennial flowering plant, deciduous |
|---|---|
| Family | Asteraceae |
| Mature height | 40–90 cm (16–35 in) |
| Mature spread | 30–50 cm (12–20 in) |
| Spacing | 40 cm (16 in) centre to centre |
| Sun | Full sun, at least 6 h of direct sun a day |
| Water | Low; drought tolerance moderate, waterlogging tolerance none |
| Soil pH | 5.5–8 |
| Cold hardiness | About -30 °C (-22 °F) once established (roughly USDA zone 4) |
| Heat stress | Likely above about 30 °C (86 °F) |
| Flowering | from about June for 9–13 weeks (northern hemisphere; later in cold climates, earlier in warm ones) |
| Wind tolerance | Moderate |
| Pollinator value | High |
| Edible | Not grown as food |
| Native to | Western and central Europe (meadows, road verges) |
| Common in gardens of | 🇬🇧 United Kingdom, 🇫🇷 France, 🇩🇪 Germany |
| Invasive in | Parts of North America: check local rules before planting |
Is Common knapweed toxic?
- People: not known to be toxic
- Cats: not known to be toxic
- Dogs: not known to be toxic
No toxicity reported in ASPCA or standard poison references.
If a child or pet may have eaten part of a plant, call a poison centre or vet straight away.
Companion planting: what to grow with Common knapweed
No well-documented helpful pairing. Group it with plants that like full sun and low water.
See Common knapweed in a botanical garden
It grows in this sample garden, which you can walk through in 3D:
- Kew: glasshouses and rock garden (30 plants)
Questions about Common knapweed
- How far apart should I plant Common knapweed?
- About 40 cm (16 in) apart, centre to centre. A mature plant spreads 30–50 cm (12–20 in).
- Does Common knapweed need full sun?
- Full sun: at least 6 hours of direct sun a day.
- How much water does Common knapweed need?
- Low water. Drought tolerance is moderate and waterlogging tolerance none.
- How cold-hardy is Common knapweed?
- It tolerates about -30 °C (-22 °F) once established, roughly USDA zone 4.
- When does Common knapweed flower?
- From about June for 9–13 weeks (northern hemisphere; later in cold climates, earlier in warm ones).
- Is Common knapweed poisonous to cats and dogs?
- For cats it is not known to be toxic; for dogs not known to be toxic; for people not known to be toxic. No toxicity reported in ASPCA or standard poison references.
- What grows well with Common knapweed?
- There is no well-documented companion pairing for Common knapweed. Group it with plants that like the same sun (full sun) and water (low).
Sources and evidence
Evidence grade B (B: extension service or peer-reviewed).
- Wildflowers and meadows, Plantlife (UK)
- Plants of the World Online (taxonomy, native range), Royal Botanic Gardens, Kew
Notes and assumptions
- Thistle-like purple heads without spines; one of the best nectar sources in a British meadow.
Reference values for planning, not horticultural, veterinary or medical advice. Varieties, soils and local climates differ: check with a local nursery or extension service.
Related plants
- Lettuce Lactuca sativa
- Sunflower Helianthus annuus
- French marigold Tagetes patula
- Zinnia Zinnia elegans
- Cosmos Cosmos bipinnatus
- Purple coneflower Echinacea purpurea
- Black-eyed Susan Rudbeckia hirta
- French tarragon Artemisia dracunculus