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Pruning Trees and Shrubs
by Andrew Holsinger
March 17, 2013

As temperatures rise and spring approaches, thoughts of pruning emerge in the minds of gardeners, said a University of Illinois Extension horticulture educator.

“There always needs to be a purpose to your pruning,” explained Andrew Holsinger. “Pruning is not only a mechanical process for removing plant growth, it is also a mental process of knowing what to remove and how and when to remove it.”

Proper pruning is important to plant health and depends on the type of plant, the plant’s health, and what the gardener hopes to gain from pruning. Some reasons for pruning are to maintain aesthetic characteristics, remove diseased or dead limbs, or improve structural stability.

It should be understood that when tree and shrubs are pruned, they are wounded, exposing underlying tissues to possible canker pathogens, disease, and decay microorganisms. Proper sanitation is a key to prevent pathogens from spreading to healthy trees and shrubs.

“Pruning may be a process that happens over the course of time,” he said. “Therefore, we should exhibit patience in pruning and think about the process before mistakes are made.”

We have much diversity in the landscape because all plants are not alike. Therefore, we cannot take a “one lopper fits all” approach to pruning.

Pruning of deciduous trees is often done in the winter when the leaves are gone. Needle evergreens should be pruned in late spring after the new growth has begun to harden off.

“Sap may ooze from pruning wounds, especially with maples,” Holsinger explained. Tree oozing can attract insects that carry diseases. To avoid it, prune in early winter when sap is not flowing throughout the tree canopy.

Be careful with flowering shrubs. “You need to recognize that spring-flowering shrubs bloom on one-year-old wood,” Holsinger said. “If you eliminate the one-year-old wood that produces the flowers, you will effectively be eliminating the flowers.” Examples of spring-flowering shrubs include barberry, lilac, forsythia, and viburnum.

Summer-flowering shrubs bloom on new wood that grows in the same season. Shearing these shrubs also removes the potential for flowering. Examples of summer-flowering shrubs are hydrangea, buddleia, mock orange, Bulmald and Japanese spirea and shrub dogwoods.

Light penetration is important for flower bud initiation. Removing older canes allows sunlight to penetrate into flowering shrubs. This results in a more effective display of flowers, instead of flowers just at the top where sunlight is sufficient.

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