Pruning Summer-flowering Trees and Shrubs
Contact: Diane Relf, Extension Specialist, Environmental Horticulture
August 1996
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.)