Yarrow (Achillea millefolium) is a resilient perennial herbaceous plant found globally in temperate regions. Whether yarrow is considered a welcome addition or a bothersome weed depends entirely on the specific landscape and individual gardening preferences. Its classification is highly contextual, moving between a desirable native plant and a persistent lawn invader.
How to Identify Yarrow
The most distinctive feature of yarrow is its delicate, fern-like foliage, which gives rise to its species name, millefolium, meaning “thousand leaves.” These finely divided, feathery leaves are typically dark green or gray-green and arranged spirally along the stem. They often feel slightly hairy and can grow up to eight inches long, with the largest leaves near the base of the plant.
When flowering, yarrow produces small, tightly packed blossoms in flat-topped clusters called corymbs. These flower heads are usually white, but cultivated varieties may display shades of pink, red, or yellow. The flowering stems can reach heights of one to three feet, rising above the low-growing foliage.
The structure below the soil surface is perhaps the most significant identifying characteristic when yarrow is considered a nuisance. Yarrow possesses an aggressive and extensive system of creeping rhizomes, which are horizontal underground stems. This rhizomatous growth allows the plant to spread rapidly and form dense, persistent colonies. These underground runners are the primary reason yarrow is difficult to remove, as any small fragment left behind can regenerate into a new plant.
Understanding Yarrow’s Status in Different Settings
Yarrow’s status as either a weed or a beneficial plant is determined by where it grows and the goals of the landscape manager. In manicured turfgrass, yarrow is universally considered a weed because it outcompetes traditional lawn species. It thrives in conditions that weaken turf, such as poor, dry, or compacted soils, where its deep roots and drought tolerance give it a substantial advantage.
The plant’s low-growing, feathery foliage is highly tolerant of close mowing, allowing it to survive and spread where grasses are kept short. When yarrow invades a lawn, its fine texture and grayish-green color contrast sharply with the surrounding turf, creating an uneven and patchy appearance. The extensive rhizome network enables it to quickly colonize bare spots, aggressively displacing the desired grass.
In contrast, yarrow is lauded for its ecological functions and hardiness in less-formal settings like meadows, xeriscaping, or native plant gardens. As a native species, it is highly valued for its ability to stabilize soil and prevent erosion, particularly on steep slopes. The plant is exceptionally drought-tolerant and requires minimal water or soil nutrients, making it ideal for low-maintenance landscapes.
Its flowers attract a wide range of beneficial insects and pollinators, including ladybugs, hoverflies, bees, and butterflies. Yarrow functions as an effective groundcover in dry areas, creating a living mulch that suppresses the growth of other plants. Its resilience and ability to thrive in poor soil without fertilizer contribute to its reputation as an ecologically supportive plant.
Control Methods for Unwanted Yarrow
If yarrow is undesirable, control must focus on addressing both the above-ground growth and the aggressive rhizome system. For small patches, mechanical removal is an option, but it requires diligent effort. Hand-digging must be thorough, ensuring every piece of the underground rhizome is removed, as any remaining fragment can generate a new plant.
Effective long-term management involves improving the overall health of the turfgrass, as yarrow invades weak swards. Cultural practices like regular aeration and proper fertilization create a dense, vigorous lawn that outcompetes the yarrow. Regular mowing suppresses the plant by limiting photosynthesis and preventing the formation of flowers and seeds.
For widespread or severe infestations, chemical control may be necessary using a selective, systemic broadleaf herbicide. A systemic product is essential because it is absorbed by the foliage and translocated down into the rhizomes, providing a complete kill of the root network. Herbicides containing active ingredients like dicamba or clopyralid are often effective against yarrow in turf, penetrating the plant’s defenses to reach the persistent underground parts.