Yarrow (Achillea millefolium) is a resilient, drought-tolerant perennial favored for its flat-topped flowers and feathery foliage. This hardy species spreads readily through rhizomes, or underground stems. Division is a necessary maintenance task for keeping the plant vigorous and contained. Separating and replanting portions of the root mass is the most effective way to propagate the plant and ensure its long-term health.
Recognizing When Yarrow Needs Dividing
The need for division is indicated by a decline in the plant’s appearance and flowering performance. Overcrowded yarrow often exhibits a “donut effect,” where the center of the clump dies out, leaving a ring of growth around the edges. This central sparseness occurs because the dense, woody root system restricts the flow of nutrients and water to the core.
When flower production decreases significantly, or the stems become weak and floppy, the plant is struggling due to overcrowding. Division is generally recommended every three to five years, but visual cues are more reliable than a strict schedule. The necessity for division arises from the aggressive growth of rhizomes, which can quickly exhaust localized soil resources.
Choosing the Best Time of Year to Divide
The timing of division is important because the plant needs a period of low-stress recovery to establish new roots. The two optimal windows for dividing yarrow are early spring and early fall, aligning with its natural growth cycle.
Early spring is often preferred, as divisions benefit from cool soil temperatures and spring rains, encouraging rapid root establishment before summer heat. Divide just as the first signs of new foliage emerge, before the plant puts significant energy into summer growth.
Dividing in early fall is an equally effective opportunity for maintenance. This window opens after the plant has finished its main flowering period, allowing it to focus seasonal energy on root development. Fall division must be completed at least four to six weeks before the first anticipated hard frost. This ensures the separated root sections have sufficient time to anchor themselves before dormancy. Division should never be attempted during the heat of summer or when the plant is actively blooming, as the resulting stress can lead to plant failure.
The Step-by-Step Division Process
Preparation for dividing yarrow should begin the day before by thoroughly watering the clump to minimize transplant shock and loosen the soil. Start the division process by using a sharp spade or garden fork to dig a circle around the yarrow clump, approximately six to twelve inches out from the center of the plant. Carefully lifting the entire root mass out of the ground allows you to inspect the structure and identify the most vigorous outer sections.
The next step involves physically separating the clump into smaller pieces, ensuring each new division possesses a healthy mass of white, fibrous roots and active top growth. It is important to discard the woody, older center of the original clump, as this material is past its prime and will not produce strong new growth. You can use a sharp knife, a shovel, or even two garden forks back-to-back to pry the dense root mass apart.
When replanting the new divisions, work some fresh organic material into the soil of the new location to provide a nutrient boost. Plant the new sections at the same depth they were previously growing, ensuring the crown is not buried, and space them about one to two feet apart to allow for future spread. Immediately after replanting, give the divisions a deep, thorough watering to settle the soil around the roots and eliminate any air pockets. For the first few weeks, providing the new plants with consistent moisture and slightly reduced sun exposure will aid their recovery and establishment.