Summer-flowering shrubs bloom on the new wood that grows in the spring. Therefore, early spring is the best time to prune summer-flowering trees, shrubs, and vines. If pruning is performed later, after new growth has begun, many flower buds will be removed, thus reducing, and possibly precluding, an attractive flower show.
On the other hand, spring-flowering trees and shrubs form flower buds on the wood that grows in the summer. Therefore, pruning on early spring-flowering plants should be delayed until after they have bloomed (or as the blooms start to fade).
Why Prune?
The most important reason for pruning flowering shrubs, and to a lesser extent trees, is to maintain a large portion of the plant as young, vigorous wood. Since most flower buds are formed on current or previous year's growth, it is useful to remove one third of the oldest wood annually to keep the plant vigorous. Such pruning will stimulate future flower and fruit development. Many flowering plants, such as rhododendrons and azaleas, produce more flowers if old flowers and fruit clusters are removed.
Prune to remove dead, diseased, and/or broken branches. This type of pruning can be done any time of the year when unhealthy branches are identified.
Prune to rejuvenate old shrubs and restore them to new vigor. Certain shrubs, even though badly overgrown, can be restored to a young, natural growth habit by the proper use of rejuvenation pruning (the entire shrub is cut back to the ground). Lilac, privet, and many of the spireas are shrubs that can be rejuvenated. However, this type of pruning may cause over-vigorous growth that is susceptible to injury or that looks out of proportion.
Prune to create formal or unusual shapes. Espaliers, hedges, and shrubs used in formal plantings are pruned or sheared into shapes other than their natural growth habits. This should never be done on flowering shrubs.
Prune to prevent damage to people and property. Branches that are weak or too low over houses, sidewalks, or parking areas should be removed.
Probably the worst reason to prune is to maintain or reduce the size of a tree or shrub to try to keep landscape plantings in proper scale. If possible, it is best to replace the plant with another of the proper size and variety.
Pruning Tips
The most rapid healing of a tree pruning wound occurs when the cut is made just outside the branch collar. The collar is the slightly swollen area where the branch joins the trunk or another large branch.
When simply shortening a small branch, make the cut at a lateral bud or another lateral branch. Choose a bud that will produce a branch that will grow in the desired direction (usually outward). Cuts should be made at a slight angle about one-quarter inch beyond the bud.
Never leave stubs as they prevent effective healing of the wound. The stub dies back, providing an entry point for disease and rot organisms.
Recent research suggests that pruning wounds heal more effectively without the application of pruning paints or other such materials. These products may be a waste of time and money when used for purposes other than aesthetics.
Pruning tools must be kept sharp and clean. One-hand pruning shears with curved blades (secateurs) work best on smaller branches.
Flowering shrubs need only light pruning during the first year or two after planting. Thin out by cutting older branches back to the ground. Annual, selective pruning of shrubs eliminates the need for drastic pruning.
Ornamental shrubs should not be sheared unless an unnatural form is desired. Shearing will reduce the number of blooms on a flowering shrub.
Some summer-flowering plants that should be pruned in early spring include Glossy Abelia (Abelia grandiflora), Butterflybush (Buddleia), Beautyberry (Callicarpa), Clematis (Clematis), Shrub Althea (Hibiscus syriacus), PeeGee Hydrangea (Hydrangea quercifolia), Goldenraintree (Koelreuteria paniculata), Hybrid Tea Rose (Rosa), and Crapemyrtle (Lagerstroemia).
(Originally published as "Pruning Summer-flowering Trees and Shrubs," by Ellen S. Bennett, Extension Technician, Consumer Horticulture, Virginia Tech, in The Virginia Gardener Newsletter, Volume 12, Number 3.)
