The Dividing Perennials Web page from Clemson Extension provides a very helpful guide to dividing many types of perennials. A useful chart is included listing various perennial plants and guiding you as to how often they may need dividing, what time of the year and the best method to use.
Tool or Gardening Product
Border Spade & Border Fork
These two tools are smaller versions of their larger cousins the standard-sized spade and fork. However their small size makes them especially useful for working in small spaces and for dividing perennial plants. Don't overlook this smaller tools when shopping for your next great addition to the garden shed!