Giant knapweed (Centaurea macrocephala) Genus:  Centaurea This clumping, robust perennial has unusual ramrod-stiff flower stems that bloom from early summer through late summer. Its fat, rusty buds open into large, deep yellow thistle flowers the size of a small fist. Easy to cut and dry for arrangements. This plant has big, coarse leaves that call for strong companions. Noteworthy Characteristics:  A tricky plant to work into a perennial garden because it draws a lot of attention. Care:  Grow in moist soil in sun or partial shade. Propagation:  Start seeds in a cold frame in spring, or divide plants in spring or fall. Problems:  White mold, rust, mildews, thread blight, and Southern blight.

Overview

Height 3 ft. to 6 ft. Spread 1 ft. to 3 ft. Growth Habit Clumps Light Full Sun to Part Shade Moisture Medium Moisture Characteristics Showy Flowers Bloom Time Summer Flower Color Yellow Uses Cottage Garden, Cut Flower Style Rock Garden Seasonal Interest Summer Interest Type Perennials