Western Yarrow (Achillea millefolium var. occidentalis)

By Terri Smith

Achillea (pronounced ah-KILL- ee-ah) is a flowering perennial in the Aster family (Asteraceae). Named after the great mythological Greek warrior Achilles, the plant was purported to be used as a remedy for bleeding wounds during the Trojan War. Millefolium is Latin for “thousand leaved” and refers to the fern-like, highly dissected foliage. The variety name occidentalis means “western.”

Western yarrow is a highly adaptable wildflower that ranges from Canada to California and into the Great Plains. It is often confused with common yarrow (Achillea millefolium var. millefolium), which was originally found in Eurasia, Europe, and Scandinavia. More than 85 varieties of common yarrow were introduced to North America during early colonial times. Western and common yarrow readily hybridize.

Western yarrow grows erect to a height of 1 to 2 feet in contrast to most common varieties which normally have a taller stature. The leaves of the western plant are densely hairy, an adaptation to drought and heat. The leaves of common yarrow are sparsely hairy. The umbels (flat flower heads) of western yarrow are white to pale pink and bloom all summer. Common yarrow cultivars are available commercially in a wide range of warm colors with a shorter and later blooming period than western yarrow. Judith Phillips states that the “western native is the toughest." The plant grows wild at the Leonora Curtain Wetland Preserve where it mingles with the cattails and watercress near the stream bed.

Many beneficial insects such as butterflies, native bees, lady beetles, minute pirate bugs and hoverflies are frequent visitors to the flat landing pads of western yarrow flowers. Finley and Nieland list the plant as a larval host for Chalcedon checkerspot and painted lady butterflies.

Landscape Use: Western yarrow can be seeded to create a flowering “lawn” in sunny naturalized areas (mow occasionally with the mower set on high). To increase species diversity, the seeds can be added to native wildflower or grass seed mixtures in naturalized and low maintenance areas. Seeding or planting along the inner raised edges of a rain garden, where periods of flooding are usually short and intermittent, would invite more pollinators to the garden.

Planting and care: Seeds germinate readily in spring when planted shallowly. Water lightly until established. New plants produce few flowers in the first year. Drought tolerant by second or third year. Survives with little maintenance. Deadheading spent flowers is advised for longer bloom time.

Propagation: Easy from seed. Lightly cover seed with soil. Sow anytime. Established plants spread by rhizomes so digging up divisions of plants also works well.

Plant type: Herbaceous perennial

Bloom time: May through September

Size: 1- to 2-feet tall and wide

Sun: Full sun

Soil: Disturbed soils, gravelly loam, thin sandy soils, alkaline caliche

Water: Very drought tolerant once established. Can become invasive with too much water.

USDA Zones: 3-9

Elevation: 5,500 to 11,000 feet

References:

Phillips, Judith. “Growing the Southwest Garden.” Timber Press. 2015.

Willa F. Finley and Lashara J. Nieland. “Land of Enchantment Wildflowers.” Texas Tech University Press. 2013.

Tucker, Janice. Santa Fe Botanical Gardens Plant of the Month. March 2011.