Mainstays of the summer perennial border, yarrows offer showy blooms and finely cut, aromatic foliage. Their flat-topped flower clusters are excellent for drying. Though often considered carefree, they do require excellent drainage, especially in high-rainfall, high-humidity areas; planting in heavy clay usually results in rot. Once established, they thrive in drought and heat. Seldom browsed by deer. Cut back plants after they finish blooming. Divide and replant clumps every 3 years in late winter.
A. ageratifolia (A. serbica). GREEK YARROW. Native to Balkan region. Low, foot-wide mats of silvery leaves, toothed or nearly smooth edged. White, 12- to 1-in.-wide flower clusters are carried on stems 410 in. tall.
A. clavennae. SILVERY YARROW. Native to Europe. Silvery gray, silky leaves, lobed somewhat like chrysanthemum leaves, form mats about 8 in. wide. Loose, flat-topped clusters of 12- to 34-in.-wide, ivory-white flower heads on 5- to 10-in. stems. Often sold as A. argentea.
A. filipendulina. FERNLEAF YARROW. From the Caucasus. Tall, erect plants 45 ft. high and to 3 ft. wide, with deep green, fernlike leaves. Bright yellow flower heads in large, flat-topped clusters. Dried or fresh, they are good for flower arrangements. Several selections are available. 'Gold Plate' grows up to 5 ft and has flower clusters up to 6 in. wide; hybrid 'Coronation Gold', to about 3 ft. high, also has large flower clusters. 'Cloth of Gold' has large flowers and intermediate height.
A. millefolium. COMMON YARROW. Native to Europe, western Asia. Erect plant with narrow, green or grayish green leaves and flat-topped white flower clusters on 3-ft. stems. Spreads by underground runners. Many selections are available. 'Fanal' ('The Beacon') and 'Rosea' are bright rose-pink; 'Cerise Queen' is deeper pink; 'Lilac Beauty' ('Lavender Beauty') lavender-pink; 'Weser River Sandstone' rose-pink fading to tan; and 'Salmon Beauty' ('Lachs-schnheit') salmon-pink. 'Hoffnung' ('Great Expectations') is pale yellow; 'Fire King', 'Pretty Woman', and 'Paprika' are red (with yellow center) aging to coppery red. 'Feuerland' ('Fireland') is salmon-peach, and 'Peggy Sue' is apricot.
Worthwhile seed-grown garden strains and hybrids include 'Apfelblte' ('Appleblossom'), 'Martina', 'Terracotta', the Summer Pastels series ('Strawberry Seduction', 'Sunny Seduction', 'Peachy Seduction'), the Summer Berries series, and the Desert Eve series.
A. ptarmica. SNEEZEWORT.From Europe, Asia. Erect plant to 2 ft. high and wide. Narrow leaves with finely toothed edges. White flower heads in rather open, flattish clusters. 'The Pearl' and 'Ballerina' have double flowers.
A. tomentosa. WOOLLY YARROW. From Europe, western Asia. Makes a flat, spreading mat (to about 112 ft. wide) of fernlike, gray- green, hairy leaves. Golden flower heads in flat clusters top 6- to 10-in. stems. 'King George' has cream blooms. A good edging and a neat ground cover for small areas with good drainage; used in rock gardens. Shear off dead flowers to leave an attractive gray-green mat.