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Horticulture and Home Pest News
Horticulture & Home Pest News is filled with articles on current horticulture, plant care, pest management, and common household pests written by Iowa State University Extension specialists in the Departments of Entomology, Horticulture and Plant Pathology.

Pruning Formal Hedges

This article was published originally on 3/17/2010

There is something special about a healthy, well maintained hedge. A symmetrical wall of green creates visual and physical limits in the landscape and provides a softer effect than wood or plastic materials. Hedges are an effective backdrop for flower beds and borders or may stand on their own in a diversity of shapes and sizes. Shrub plantings can be allowed to grow into a natural, informal hedge or they may be pruned (sheared) into a formal hedge. Shrubs suitable for small hedges (less than 5 feet in height) include barberry (Berberis), boxwood (Buxus), inkberry (Ilex), and alpine currant (Ribes) while Privet (Ligustrum), lilac (Syringa), yew (Taxus), and arborvitae (Thuja) can be utilized as tall hedges (those greater than 5 feet in height). 
Maintaining a formal hedge
 
Formal hedges are beautiful when well kept, but if they are not properly maintained they may become overgrown, poorly-shaped eyesores. Maintaining a formal hedge is time-consuming and requires proper pruning techniques. First, pruning must be done regularly to maintain the desired shape. Second, it is important to shape a formal hedge so that it is narrower at the top than at the bottom. A pyramidal shape allows the lower branches and leaves to receive the sunlight that is required to produce a dense, full hedge from top to bottom. Finally, it is important to know the natural growth habit and height of the shrub species. For example, trying to keep a typical privet hedge lower than 3 feet may be frustrating. The plant grows so quickly that it will require frequent pruning to maintain the desired height.
 
When to prune
 
Proper timing is important when pruning hedges. Extensive pruning of most deciduous hedges is best done late in the dormant season (late February and March in Iowa). However, pruning a spring-flowering hedge, such as lilac, during the dormant season will remove many of its flowers. It’s usually best to prune spring-flowering shrubs immediately after blooming. Early spring (April) is usually the proper time to begin pruning evergreen hedges. Regardless of when pruning begins, most deciduous and evergreen hedges will need to be pruned 2 to 4 times (possibly more) during the growing season to keep them well-shaped and attractive. 
 
 
Lilac and dogwood hedges (left, right, respectively) will not require as much pruning as a pine hedge (center).
Lilac and dogwood hedges (left, right, respectively) will not require as much pruning as a pine hedge (center).
 
Different pruning styles and species can be mixed to create a variety of hedges
Different pruning styles and species can be mixed to create a variety of hedges