University of Illinois Extension
Dividing - Stepping Stones to Perennial Garden Design - University of Illinois Extension

Dividing

The definition of plant division is plant propagation by dividing parts (crowns, suckers, tubers) and planting segments capable of producing roots and shoots. Many vigorous perennials crowd themselves or invade areas where they are not desired, choking out surrounding plants, thus requiring division. Most of the time, perennial gardeners aren't dividing for plant propagation purposes, but for keeping things in their place. Division for the most part is done when the plants are dormant. Here in Illinois, spring division is most often recommended. This avoids subjecting the new divisions to harsh winter temperatures and reduces the chances of heaving (lifting of shallow rooted or poorly established plants from the ground as the soil freezes and thaws).

Dividing Hostadividing Hosta

Methods of dividing vary according to the plant. In general, vigorous new shoots from the outside of the clump are preferred for replanting, but all shoots will do.

The soil should be moist for easy digging. Water the bed a few days before if dry. In the spring this is usually not a problem. You should wait, however, until the soil is thawed. Dig out the entire clump. Divide the healthy living portion into smaller clumps either by pulling them apart or cutting them apart. Some dense clumps may need a handsaw to divide! Replace one or two healthy divisions in the original planting site. Share the remainder with a friend, plant elsewhere or discard.

Do your research. Some plants are better if left undisturbed for many years. Gas plant (Dictmanus albus), lupines (Lupinus sp.), baby's breath (Gypsophilia paniculata), false indigo (Baptisia australis) and butterfly weed (Asclepias tuberosa) all do much better if left alone for many years.

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The basics you learned here should influence all your landscape decisions. Remember there is always something else to learn, and no one knows everything. Keep an open mind to different opinions and ideas. Gardening is a love of plants and a passion for beauty - share this with others.

"The enjoyments of a garden being so manifold and continuous, bringing brightness to the home, health to the body, and happiness to the mind, it is for us, who have proved them, whose daily lives are made more cheerful by their influence, out of our gratitude and our goodwill, to invite and to instruct others, that they may share our joy."
-- S. Reynolds Hole from Our Garden