Division is one of the easiest propagation techniques, and may be used not only to increase plant stocks and but also to regenerate tired-looking herbaceous perennials and keep them vigorous and flowering freely. Many perennials deteriorate over time, slowly dying out in the centre, unless they are lifted and divided every three or four years.
There are two major techniques used for dividing perennials: the most commonly used is for fibrous-rooted plants such as Michaelmas daisies (Aster spp.), whereby the plant is split into many smaller sections using a garden fork. The healthiest sections (around the outside of the clump) are replanted.
The second technique is used for rhizomatous plants, such as lilies and irises; they are divided by pulling apart the newer portions of rhizome, which are then replanted in shallow soil.