The best time to divide hostas is late summer, but it can be done in the spring through the fall. Dividing hostas in late summer gives the plants enough time to recover from the shock of dividing before the ground freezes in winter.
Experienced gardeners know to divide hostas when the center of the clump dies. Typically, division is done every three years. If dividing hostas in the summer, the new divisions must be watered well for a few weeks.
Gardeners and hobbyists dig up small clumps entirely before dividing. The best way to divide large clumps is with a shovel while still in the ground. The divisions are then lifted and replanted.