This grower is sure of this plant identification.
5' plus, clump forming.
Easy to grow.
Loves sun and butterflies
Cephalaria gigantea (Giant scabious). A spreading perennial native to Caucasus and Northern Turkey. It's 4,5cm long, dark green leaves are pinnatisect, oblong and toothed. Can grow to heights of 2.5m. Bright yellow flowerheads emerge in summer, approximately 5 cm in diameter.
They are fully hardy and will prefer sun and well drained soil.