Reasons and Times to Prune Landscape Plants

By C  Rae Hozer, Cumberland County Master Gardener

February and March are generally good months to prune landscape plants. Of course, not all trees, shrubs or vines require regular pruning. Some never need trimming. Good reasons to get out your pruning saw and loppers are a need for shaping or thinning, poor growth patterns such as crossed branches that rub, and to remove diseased limbs or those hurt by winterkill or storms.

When pruning is justified, consider typical growth characteristics of individual species to determine just when and how to go about the process. In some cases the life cycle of pests and pathogens known to attack that plant should influence timing, as well.

Dead or dying branches caused by storms and vigorous upright growth (“suckers”) may be cut back as needed. However, be cautious about cutting off diseased branches when plants are actively growing. Wait until trees and shrubs showing signs of disease are dormant, then prune. Also, routinely disinfect equipment between cuts. Use a spray bottle with rubbing alcohol to clean blades then wipe them with a cloth. A 10% bleach with water solution disinfects equally well, but may damage clothing and rust pruners.

Is the plant to be trimmed evergreen (having leaves or needles in winter) or deciduous (drops leaves in autumn and puts out new foliage the following year)? Evergreen branches from pines or hollies can be cut in winter and used in decorative arrangements in or around your home. You get a good view of a deciduous plant’s shape while there are no leaves. Check the structure. Thin out overly dense central growth. Fruiting and flowering species benefit when air flows well to the interior and lots of sunlight reaches middle branches.

For woody plants that  produce desirable flowers, blossom time signals when to prune. In general, cut back spring-flowering ornamentals shortly after blooms fade. These plants form flower buds for this spring during the prior year. Cutting their branches back late in the year removes those buds, decreasing their floral display in spring. Trees and shrubs that flower in mid-summer or in autumn develop buds for blossoms earlier the same year. Pruning encourages new growth near the site of each cut. Winter or early spring trimming can increase the number of new shoots where flower buds form, making the summer / fall floral display better.

Forsythia and lilac bushes are spring bloomers that send up new stems every season. As each clump spreads, less light reaches the center. Sunlight is essential for flower bud formation. Soon there are blossoms only at the sides and top. Renew them by cutting one third of the older canes to the ground and trimming branch tips back after they finish blooming. The increased flower production the following spring can be startling.    

Maple, birch and dogwood trees respond to pruning in spring by putting out lots of sap (“bleeding”). That doesn’t look good, may delay healing of pruning cuts and in some cases insects carrying infectious plant diseases are attracted by the sap. Pruning these trees while plants are dormant helps to avoid oozing sap and few insects are active in winter.

Plateau Gardening is written by Master Gardeners for those tending home landscapes and gardens in Tennessee’s Upper Cumberland Region. Contact UT Extension Cumberland County, P.O. Box 483, Crossville, TN 38557, (phone 931-484-6743) for quick answers to specific questions, free publications, or to learn about becoming a Master Gardener. Email comments or yard and garden inquiries to Master Gardener Rae, mgardenerrae@frontiernet.net.