Yarrow (Achillea millefolium) is a common flowering plant recognized by its distinctive, flat-topped flower clusters, known as corymbs. The natural color of yarrow is typically white or cream, which is found in wild landscapes across the Northern Hemisphere. Extensive horticultural breeding over time has dramatically expanded this palette, introducing a vibrant range of colors that are popular in garden settings.
The Native Palette
The species Achillea millefolium is characterized by flowers that are most often white or creamy white. This native form is commonly seen growing in fields, along roadsides, and in naturalized areas. The coloration is sometimes a grayish-white or occasionally possesses a slight pinkish or purplish tinge, but the overall impression is pale.
The overall color appearance is created by numerous tiny individual florets clustered tightly together in a flattened head. Each flower head resembles a miniature daisy, composed of a small number of ray florets surrounding a center of disc florets. The ray florets, which are the small petal-like structures, are typically white, while the disc florets in the center may be whitish, grayish, or pale yellow.
The Cultivated Color Range
Selective breeding has transformed yarrow into a garden perennial with an impressive and stable range of flower colors. The spectrum now includes brilliant shades far beyond the native white and cream.
Deep reds and vibrant pinks are well-represented, with varieties like ‘Red Velvet’ offering intense, saturated color. Other selections, such as ‘Cerise Queen,’ feature striking deep pink flowers. The yellow range is also extensive, featuring bright, clear shades like those found in ‘Moonshine,’ a popular cultivar known for its pale, shimmering yellow flowers.
The color palette expands further into warm tones, including apricots, oranges, and terracotta shades, sometimes fading to a warm gold as they age. Many hybrids exhibit a dynamic color shift, where the flowers open in a deeper shade and then gradually lighten, creating a multi-toned effect on the same plant.
Factors Influencing Flower Hue
The diverse colors in yarrow are primarily determined by two main classes of pigments: flavonoids and carotenoids. Flavonoids are responsible for the pink, red, and purple hues, while carotenoids contribute to the yellows and oranges. The specific combination and concentration of these compounds, which are genetically controlled, result in the stable color of a particular cultivar.
Environmental factors, particularly intense sunlight, can cause visible color changes as the flowers mature. In many pink and red varieties, the vibrant pigments can break down under strong sun exposure, leading to a noticeable fading or “bleaching” to a lighter pink or cream color over the bloom period.
Unlike some other garden plants, like hydrangeas, the flower color of yarrow is not significantly altered by soil pH or nutrient levels. While rich soil may cause the plant to grow taller and potentially flop over, it does not chemically change the flower hue. The pigment expression in Achillea is governed by internal plant chemistry and light exposure, not the soil’s acidity.