Centaurea macrocephala (Giant knapweed): Huge, bright yellow almost fluffy flowers in mid-summer follow attractive papery buds. Attractive to bees. Height to 1.5m. Hardy.

Cephalaria gigantea (Giant scabious): Very tall wavy stems topped with large lemon yellow scabious-like flowers.Easy to grow. May need staking or support. Hardy. Up to 2m.