As clump-forming perennials mature, they often become overcrowded, competing among themselves for light, water and nutrients. This typically results in fewer blooms, said David Trinklein, state ...

This undated photo shows a clump of irises being divided in New Paltz, N.Y. Overgrown clumping perennials such as iris can be rejuvenated and brought down to size by dividing the clumps into smaller ...