Yarrow (Achillea species) is a resilient perennial herb that features feathery, aromatic foliage and distinctive flat-topped flower clusters. This popular garden plant is widely recognized for its ability to thrive in tough conditions. Yarrow’s mature height is highly variable, differing significantly depending on both its genetics and its environment. Understanding the factors that determine this size is helpful for gardeners planning their perennial borders.
Typical Height Range of Common Yarrow
For the basic garden varieties of Common Yarrow, Achillea millefolium, the typical height range falls between 1 and 3 feet (30 to 90 centimeters). This range represents the average stature of the plant when growing in non-optimized or wild settings. The plant is an upright, herbaceous perennial that produces stems from a spreading rhizomatous root system. Under favorable conditions, the common species can grow up to 40 inches (approximately 1 meter) tall. This baseline measurement is primarily driven by the plant’s genetics, which determine its maximum potential size.
Height Variations Among Specific Cultivars
Genetic selection through breeding has created a vast array of yarrow cultivars that deviate significantly from the common species height. Dwarf varieties are specifically bred for compact growth, making them ideal for containers or front borders. Cultivars like ‘Little Moonshine’ or Achillea tomentosa often mature at a height of only 6 to 12 inches. Conversely, hybrid yarrows and different species crosses can achieve a much loftier stature. Taller varieties, such as ‘Coronation Gold,’ can easily reach 30 to 36 inches, or in some cases, up to 4 feet tall.
Environmental Factors Influencing Height
External growing conditions play a significant role in pushing yarrow toward its genetic height potential or keeping it stunted. Yarrow performs best in full sun, which encourages sturdier, more robust growth; conversely, growing yarrow in partial shade causes the plant to stretch, resulting in weak, “leggy” stems that are prone to flopping over. The composition of the soil also heavily influences the plant’s vertical growth habit. Yarrow naturally thrives in lean, well-drained, and somewhat poor soils. Rich or overly moist soils, particularly those high in nitrogen, often lead to excessive foliage growth and taller, weaker stems that struggle to remain upright.
Managing Height Through Active Maintenance
Gardeners can actively manipulate the plant’s height and habit using specific pruning techniques. The “Chelsea Chop” involves cutting back the stems by about one-third in late spring, before flowering begins. This technique reduces the final height of the plant and encourages a bushier growth habit with stronger stems that are less likely to flop. Removing spent flower heads, known as deadheading, prevents the plant from expending energy on seed production and often encourages a second, shorter flush of growth and bloom later in the season. Additionally, dividing mature, crowded clumps every two to three years rejuvenates the plant, preventing the older, weaker center growth that can lead to excessive height and flopping.