Yarrow (Achillea millefolium) is a highly valued perennial known for its resilient nature and attractive clusters of tiny, tightly-packed flowers. This plant is a popular choice for home gardeners due to its low maintenance needs and remarkable tolerance for dry conditions. Understanding the specific requirements for yarrow cultivation allows for maximum flower production and helps maintain the plant’s tidy appearance in the landscape. The following instructions provide a comprehensive guide to successfully growing and caring for this durable garden addition.
Site Selection and Soil Requirements
The most significant factor in cultivating healthy yarrow is ensuring it receives sufficient sunlight, meaning at least six hours of direct sun daily. Full sunlight encourages compact growth and abundant flowering; plants in partial shade tend to become elongated and floppy. Yarrow is highly adaptable to various soil textures, but excellent drainage is paramount. The plant will not tolerate constantly saturated conditions, which quickly leads to root rot. Yarrow thrives in poor or lean soil, which keeps the growth habit dense and upright. Planting in overly rich soil or heavily amending the site is discouraged because it promotes weak stems and leggy growth, often requiring staking. The plant can manage a wide range of soil pH levels, but the focus should remain on facilitating rapid water runoff.
Essential Maintenance: Watering and Fertilization
While newly planted yarrow requires consistent moisture to establish a robust root system, established plants are exceptionally drought-tolerant. During the first growing season, frequent watering is needed until the root system has fully developed. Once established, yarrow rarely needs supplemental irrigation and prefers its soil to dry out completely between watering sessions. Overwatering is the single greatest threat, increasing the risk of root rot and powdery mildew. If the plant receives less than one inch of rainfall per week during the summer, a deep, infrequent watering is sufficient.
Regarding nutrient input, yarrow rarely requires fertilization, performing best when grown in average to poor soil. Adding rich compost or applying high-nitrogen fertilizers should be avoided, as this results in weak stems and may decrease the overall number of blooms. If the soil is exceptionally poor, a very light application of a balanced, slow-release fertilizer in early spring may be considered, but most gardeners find this unnecessary.
Controlling Growth Through Pruning and Deadheading
Pruning is important for yarrow, primarily to encourage repeat blooming and manage the plant’s naturally aggressive growth habit. Deadheading, which involves removing the spent flower clusters, should be done regularly throughout the summer to prevent the plant from diverting energy into seed production. Snipping the faded flower heads back to a lateral bud or a main stem will encourage a subsequent flush of blooms and maintain a tidier appearance. This action also helps prevent unwanted self-seeding, which is useful if a specific cultivar is being grown.
A substantial mid-season cutback, often called the “Chelsea chop,” can be performed in late spring or early summer. This technique involves cutting the entire plant back by approximately one-third of its height. The Chelsea chop encourages the plant to produce a bushier, more compact form with stronger stems that are less likely to flop over later in the season. It also effectively staggers the bloom time, often resulting in a more prolonged overall display.
At the end of the growing season, a final pruning is necessary to prepare the plant for winter. This involves cutting all the stems back close to the ground, leaving only the basal foliage—the low cluster of leaves at the plant’s base. This late fall or early spring cutback removes old foliage and allows new, fresh growth to emerge unhindered the following year.
Long-Term Health: Division and Winter Preparation
Because yarrow spreads vigorously via rhizomes, dividing the clumps is necessary every three to five years to maintain plant vigor and prevent overcrowding. Over time, the center of an established clump can become woody and less productive, leading to fewer flowers. Division rejuvenates the plant, ensuring a strong display in the garden.
The best time to divide yarrow is in the early spring just as new growth is emerging, or in the early fall. To divide, the entire clump should be lifted out of the ground. Separate the outer, more vigorous sections using a sharp spade or knife, discard the woody center, and replant the younger, healthier sections.
Yarrow is resistant to most common garden pests and diseases, but it can occasionally develop powdery mildew, especially in conditions of poor air circulation or high humidity. Regular division and proper spacing help mitigate this issue by promoting airflow around the foliage. The plant is cold-hardy, typically surviving winter with minimal intervention. Heavy mulching should be avoided as it can trap excess moisture around the crown, which yarrow dislikes.