Giant knapweed (Centaura macrocephala
) is native to Caucaus and Turkey and is hardy in zones 3 to 8. As you know, this plant grows best in full sun and well-drained soil. The yellow flower appears for several weeks in mid summer a top a leafy stem that can reach 3 to 4 feet in height. You can divide this plant in spring as growth emerges or early fall if it has outgrown its location or you want to start new plants. This yellow bloomer works well as a specimen in the garden or as a cut flower in fresh and dried arrangements.