By James Feucht, Ph.D., Colorado State University Cooperative Extension landscape plants specialist
Early spring is a good time to do some needed pruning. Despite the advice that some gardening literature provides -- to prune spring-flowering trees and shrubs after bloom -- much pruning can be done in the early spring.
You'll want to avoid top pruning, however, because plants such as lilacs, forsythia, mockorange, honeysuckle and some of the spireas form flower buds on growth produced from the previous year. Any top pruning will result in loss of flowers.
You can, however, thin overgrown shrubs by removing some of the canes all the way to the ground. This lets some light into the middle of the plant and prevents the "leggy" look that can come when shrubs become overgrown.
A good general rule is to remove one-third of the oldest canes each year. Remove canes that have become too large, that are insect-or-disease ridden or that may show winter dieback. Pruning these canes leaves a healthy shrub that flowers evenly and does not develop a leggy look. The amount removed depends on the density of the canes and the length of time since the last pruning.
Thin small trees at this time, paying particular attention to broken, dead and diseased branches as well as sucker sprouts. Make cuts just outside the flare or branch "collar." The collar is the slightly swollen part at the base of the branch.
As with shrubs, avoid top pruning or giving the tree a sheared look. When top growth must be removed, make the cut at the crotch.
Avoid pruning paints or wound dressings, as they tend to harbor disease organisms.
Don't prune summer flowering shrubs, including hybrid tea roses, at this time. Pruning too early may cause growth to resume from the plant's base. This growth will be vulnerable to low temperatures that may yet come our way. Late April or early May is the best time to prune these plants.
In addition to roses, this class of shrubs includes the orange-eye butterfly, blue mist spirea and froebel's spirea. With warmer weather, these plants can be cut to a stubble and new growth will appear quickly along with an abundance of flowers.
When pruning roses, begin at the top of the canes and follow them down until you find healthy stems. Make a sloping cut just above a side bud, preferably to one that is pointing away from the center of the plant. This will direct growth outward to form a more shapely plant.
You will need appropriate pruning equipment. To prune large canes from shrubs and to thin trees, a curved drawcut pruning saw and a pair of lopping shears are necessary.
Photograph courtesy of Judy Sedbrook.
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010