You can divide hostas almost anytime, but there is no need to divide them unless they are too large for their location or you want more plants to share or use in other places in your landscape. If you decide to divide them, early spring is best. Simply dig up the plant, cut it into sections with a sharp spade or knife, and replant the sections. These plants are extremely forgiving. Make certain that each section has healthy roots and buds or shoots. Water the new transplants until they are established. A layer of mulch will help maintain even soil moisture.