Divide phlox while it still looks healthy. The most common mistake home gardeners make when growing phlox is waiting until the plant shows signs of failing or over-crowding before they divide it. As a rule of thumb, allow the diameter of the plant cluster to grow to the same width as the plant’s height before dividing it. Divide the phlox sooner if the plant becomes over-crowded, or if the center of the plant fails to bloom and produces less foliage. Divide phlox in early spring, late summer or early fall. Phlox division is most successful when done in the early spring before new growth begins, or in the late summer or early fall when flowering is done.
Dig a trench around the outside of the entire plant cluster, severing the plant’s roots with the blade of your garden shovel as you go. Chop the roots under the plant by circling back around the trench again with your shovel. Push the shovel blade into the ground, angling it to reach under the plant’s root base. Push down on the handle to lift the roots. Continue around the phlox until the cluster lifts from the ground.
Break pieces off from the outside of the cluster using your fingers to separate the roots and your hands to snap the plant crowns apart. Keep breaking divisions off until the entire plant has been divided. Use a serrated kitchen knife to cut sections off the cluster you are unable to divide the plant by hand.
Mist the roots and the newspaper lightly with water if the plants are still waiting to be planted after a couple of hours.
Space new plant clusters at least 3 to 5 feet (1 to 1. 5 m) apart. You can space the divisions at least 10 inches (25 cm) apart if you are growing smaller clumps or single phlox in a row or border.
