Most perennial plants lend themselves well to dividing. Division can be used to renew an old or overgrown plant, to get more plants for use elsewhere, or to give to friends.
Division is particularly simple with clump-growing perennials such as daylilies, Siberian iris and spiderwort. Some clumps will show the need for division by worn out areas at their centers.
Clumps can best be divided in early spring when new growth begins and the weather is still cool and damp. The entire clump can be removed from the ground and cut or pulled apart with a sharp knife, back-to-back garden forks, or by hand. Depending on the size of the clump, dividing can be done without removing it from the ground. Divide the clumps into sections having roots attached to each growing shoot.
Some mature perennials are difficult to divide, and are best left alone. Among these are monkshood, Baptisia, Dictamnus (Gas plant), Gypsophila, Hellebores, oriental poppies and plants with very woody roots like Aruncus (Goatsbeard), or Cimicifuga racemosa (Bugbane).