Yarrow (Achillea millefolium) Hardy and adaptable, yarrow produces large, flat-topped flower clusters in a variety of colors. With aromatic, feathery foliage and a long bloom season, yarrow is a hardy and reliable plant that will spread quickly in ideal conditions. Culture: Plant yarrow in full sun in well-drained soil; it performs and flowers best in soils that arent too rich. Hardy in zones 3 to 10. Bloom color is somewhat variable in when grown from seed.