Culture
Easily grown in average, evenly moist, well-drained soils in full sun. Addition of sand to the soil helps promote good drainage. Plants prefer cool summer climates and do not perform well south of USDA Zone 7. Mature plants tolerate dryish soils. Avoid wet soils. Plants may be grown from seed, and may escape gardens/naturalize by self-seeding, but are not considered invasive as is the case with some of the knapweeds. Stems may flop on taller plants. Cut flowering stems back after bloom is completed.
Noteworthy Characteristics
Centaurea dealbata, commonly called Persian cornflower or knapweed, is native to Iran and the Caucasus. It is a clump-forming perennial that typically grows to 24-30" tall with a spread to 24" wide. Pinnately-lobed basal foliage (to 18-24" long) is dark green above with whitish hairs underneath. Cornflower-like, lavender to rosy pink flowers (2-3" diameter), each flower having a deeply fringed ring of outer petals surrounding a center of paler inner petals, bloom from late spring to early summer atop stems clad with small, entire, sessile, upper leaves. Each flower head has distinctive involucre bracts. Flowers are attractive to butterflies.
Genus name comes from the Greek word kentauros meaning centaur.
Specific epithet means whitened for covered with opaque white powder.
Problems
No serious insect or disease problems. Wilt, mildews, rots, blights and rusts may occur. Watch for aphids and mealybugs.
Uses
Beds, borders, cottage gardens, meadows, wild gardens, prairies and sunny woodland margins.