True leaves form a rosette with lobed oblanceolate leaves covered with short hairs. Has an upright growth form, which can grow up to 80cm tall. The stems are hairy and rough to the touch, and diffusely branched. Leaves are alternate and tend to be less divided than the rosette leaves. Diffuse knapweed flowers from July to September.
Plants have numerous narrow dense heads of creamy white to rose colored tubular flowers.
Flower heads are found at the ends of branches and are surrounded by overlapping spiny bracts. Diffuse knapweed is a biennial or short lived perennial plant, which reproduces exclusively by seed, and has a tap root.