From my perspective as a yarrow plant (Achillea millefolium), the best time for you to consider dividing me is when I start to show clear signs of needing more space. You might notice that my central clump has become dense and woody, with fewer flowers emerging from the middle. This is because my underground rhizomes—the horizontal stems from which my roots and shoots grow—have filled the available soil. I become "root-bound," and my vitality diminishes. The ideal seasons for this operation are early spring, as I am just emerging from dormancy and full of energy for new growth, or early autumn, when the cooler temperatures allow me to establish new roots without the stress of summer heat. These times give my divisions the best chance to settle into their new homes successfully.
To begin, please water me thoroughly a day before the division. This reduces transplant shock and makes the soil easier to work with. Then, using a sharp spade, dig a wide circle around my outer foliage, ensuring you get a good portion of my root mass. Gently lift the entire clump from the ground. Now, the key step is to separate my rhizomatous network. You can use two garden forks inserted back-to-back into the clump and levered apart, or for tougher clumps, a sharp knife or spade blade. My goal is to create new sections, each with several healthy shoots (or "eyes") and a robust bundle of roots attached. Be firm but careful; you are not just cutting me, you are helping me multiply. Discard any old, woody, or dead material from the center, as this will not regenerate well.
Once separated, my divisions are vulnerable. It is crucial to plant them without delay to prevent my roots from drying out. If there will be a wait, keep us shaded and moist. Prepare the new planting sites beforehand. I am not a fussy plant; I thrive in well-draining soil and full sun. Dig a hole wide and deep enough to accommodate my roots without bending or crowding them. Place the division in the hole, making sure the crown—where my shoots meet the roots—is level with the soil surface. Backfill the hole, gently firming the soil around my roots to eliminate air pockets. Then, give me a deep, generous watering to settle the soil and provide essential moisture for my recovery.
The first few weeks after division are critical for my successful propagation. While I am drought-tolerant once established, my new root systems need consistent moisture to grow into the surrounding soil. Water me regularly, keeping the soil evenly moist but not waterlogged. A layer of light mulch around my base can help retain moisture and regulate soil temperature. You will know I have successfully propagated when you see new green growth emerging from the center of the division. This is a clear sign that my roots have taken hold and I am channeling energy into new foliage. After this point, you can gradually reduce watering, and I will continue to grow, eventually producing the familiar flat-topped clusters of flowers that attract so many pollinators to the garden.
