Achillea — Yarrow
Achillea millefolium, called common yarrow, is a sturdy, carefree, and steady bloomer from late spring through fall in Sonoma County’s Mediterranean climate. Achillea is a genus of nearly 85 perennial species, one of which will fit into any garden style: wildflower or rock garden, low-water native garden, or herbaceous border. Taller varieties are valued as cut flowers added to fresh or dried arrangements.
- Achillea millefolium, popular in gardens, is a native California species and is the species most often found in nurseries.
- Compact flower heads are in a flat cluster, frequently white or yellow, but many cultivars of common yarrow have been developed and are available in colors with distinct names, such as the popular ‘Paprika’ and ‘Moonshine.’
- Aromatic, finely divided, gray-to-green foliage usually appears feathery or fern-like.
- When not maintained common yarrow can spread rapidly and become invasive.
- Some non-native species from mountainous regions are low-growing mounds or mats.
- Achillea ageratifolia (syn. serbica) forms low mat-like tussocks of pale green foliage usually with smooth-edged margins. Taller, cream blossoms are carried on thin, wiry stems.
- Achillea x kellereri is similar but with ferny leaves in taller clumps and small daisy-like flowers.
- Species from grasslands, such as Achillea ptarmica, develop taller stems and tolerate many different soils and conditions. They have naturalized in some areas in northern regions of North America. They require moderate to occasional water until established when they become drought tolerant. All grow best in full sun and fast-draining soil.
- Achillea ptarmica ‘The Pearl,’ bears small, double, button-like white flowers on stems up to 2 ft. Rhizomes spread to create small colonies.
- Little maintenance is needed when achilleas are planted in full sun and not overwatered.
- Keep newly planted specimens moist until established; then water only infrequently. Mature plants withstand some drought.
- Remove spent flowers and trim stems back occasionally to promote repeat bloom.
- To maintain vigor and prevent unwanted spread, divide when plants become crowded.
- For some gardeners, contact with foliage may aggravate skin allergies.
- Butterflies, bees, beneficial predatory insects, and parasitic wasps are all attracted to achillea’s flattened flower heads, known botanically as corymbs.
- Named cultivars that have been bred to produce flowers in many colors attract beneficial insects similarly to the native white or pink species.