Spotted knapweed
Centaurea stoebe · Asteraceae
The gardener's calendar
Ideal time to plant spotted knapweed: set it out when the soil is neither frozen nor waterlogged, and water generously as it establishes.
ID card
- Foliage
- Deciduous
- Blooming
- June to September
- Adult size
- 24 to 32 inches tall, 16 to 20 inches wide
- Growth
- Fast
- Hardiness
- Very hardy, down to 5°F
- Origin
- Mediterranean Basin and Central Europe
- Soil type
- Well-drained, poor to average, drought tolerant
Care
Light Exposure
Install your Rhine cornflower in full sun for optimal blooming. It tolerates light partial shade but will flower less generously. This is a sun-loving plant that appreciates warm, well-ventilated locations.
Watering
Water moderately during the first year of establishment to encourage root development. Once established, this drought-resistant plant requires little additional watering, except during prolonged dry spells. Avoid excess moisture which encourages rot.
Soil
The cornflower prefers well-drained soil that is rather poor to average. It adapts easily to chalky, sandy, or stony ground. A light addition of fine compost at planting time is sufficient.
Fertilizer
A light application of balanced fertilizer in spring is enough. This undemanding plant doesn't require regular feeding. Excess nitrogen promotes foliage at the expense of flowering.
Pruning and Maintenance
Remove spent flowers as you go to extend the blooming period. In late winter or early spring, cut the plant back to 6-8 inches to encourage denser branching. Remove any dead or damaged stems.
Diseases and Pests
The Rhine cornflower is rarely subject to disease. Watch for powdery mildew in cases of excessive moisture or poor air circulation. Aphids may colonize young shoots but generally disappear with a water spray. The plant is overall very resilient.
Did you know?
The Rhine cornflower owes its common name to its historical abundance along the Rhine, where it naturally colonizes dry, sunny terrain. Its genus, Centaurea, draws inspiration from Greek mythology and the legend of the centaur Chiron who treated wounds with plants of this type. In Central Europe, it is sometimes considered an invasive species in certain open ecosystems, demonstrating its great capacity for adaptation.
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
- SunflowerHelianthus annuus
- YarrowAchillea millefolium
- Ox-eye daisyLeucanthemum vulgare
- SneezewortAchillea ptarmica
- Canadian goldenrodSolidago canadensis
- WormwoodArtemisia absinthium
Tips generated and checked by Viridia — adapt them to your local climate.