Eryngium giganteum ‘Silver Ghost’ – A striking architectural perennial with thistle-like lime green blooms with blue stamens, surrounded by silvery bracts and leaves. It is an RHS Award of Garden Merit winner and requires very well-drained soils in winter or it will rot out. Good for dried flower arranging and attracting bees. Grows 24-40″ high by 12-20″ wide. Zone 5.
Echium amoenum – Red Feathers is another structurally interesting plant with spires of carmine-red flowers that fade to pale pinks and purples. These are borne from early summer through to fall (with deadheading) and it is a native of the Caucasus Mountains. Leave a few seed heads to naturalize this short-lived perennial. Grows 12-14″ high by 8-12″. Zone 3.
Artemesia absinthium – This Wormwood is a native of Europe and the key ingredient in the mind-altering liqueur Absinthe. The silvery-grey foliage stands out at a distance while the pale yellow summer flowers are rather insignificant. It is an herbaceous perennial that thrives in poor, well-drained soils and full fun exposures. Grows 2-3′ high by 18-24″ wide. Hardy to zone 4.
Echinops ritro – An easy to grow perennial with unique bright blue spherical flowers borne from July through to September. It has deep green, thistle-like foliage and may require staking if grown in too rich a soil. Globe Thistle is an RHS Award of Garden Merit winner and can be grown from seed. Makes a good cut and dried flower. Grows 3-4′ high by 24-30″ wide. Hardy to zone 3.
Achillea millefolium – Most gardeners overlook Common Yarrow for the showier cultivars with different flower colours, but this white flowered beauty is great for naturalizing in open areas. The blooms are borne from June to September over aromatic greyish-green fern-like foliage. Good for dried arrangements. Somewhat invasive. Grows 2-3′ high by 2-3’+ wide. Zone 3.