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University of Illinois

Pruning Flowering and Formal Shrubs

FOR IMMEDIATE RELEASE
January 14, 2014

Proper pruning of flowering shrubs and formal shrubs not only increases the number of flowers but makes the plant more tidy.

It is important to identify the shrub and know the timing of flowering before any pruning or shearing takes place. Early flowering shrubs (those that flower before June 15) should be pruned after flowers fade and late flowering shrubs can be pruned in early spring when green growth starts to occur.

A note for gardeners with hydrangea in their landscape: Mophead (macrophylla)and oakleaf hydrangea should be pruned after flowering and panicled (paniculata) and smooth (arborescence) hydrangea should be pruned in late winter. A list of flowering timing is at www.hort.purdue.edu/ext/ho-4.pdf.

There are four methods of pruning shrubs: renewal, heading back, rejuvenation and shearing.

Renewal pruning is a method used on roses and multi-stemmed shrubs. It is the removal of the majority of the oldest branches all the way to the base of the plant, thinning the canopy and stimulating new growth. Renewal pruning opens up the center, allowing additional sunlight and air. Spring flowering shrubs like lilac are generally pruned by the renewal process. Other shrubs that are pruned by a renewal process are beauty bush, dogwood, hydrangea, viburnum and hypericum.

Heading back pruning means the branches are clipped back to lateral buds, making a fuller plant. Heading back provides reduction of height while maintaining the shrub's natural look. The overall goal is to prune the limb back to �¼ of an inch above the bud.

Rejuvenation cutting is used when the shrubs have become too large or have too many stems to do the renewal or heading back method. Rejuvenation cutting should occur in early spring, removing all growth back to the ground, leaving only 4 to 6 inches of growth behind. Shrubs that would respond well to this method are smoke bush, forsythia, cinquefoil, flowering quince and weigelia. This process can be employed for overgrown shrubs or shrubs that die back in the winter.

Shearing is generally not recommended for most flowering shrubs because it tears up stems and leaves stumps. However, shearing is very common for formal shrubs like boxwood, yew and privet. The largest mistake made with shearing is the shape left behind. Most shear perpendicular to the ground. However, this means sunlight is unable to reach the bottom branches, causing them to lose their lower leaves. The shape left behind should be wider on the bottom to capture the most light. If this shearing process is corrected, most shrubs will likely grow back the bottom portion of the plant.

Photos are courtesy of University of Kentucky Extension

Source: Kelly Allsup, Extension Educator, Horticulture, kallsup@illinois.edu

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