Pruning Evergreens
Pruning is an important maintenance practice for some evergreens. Evergreen plants can be divided into two broad categories: (1) narrowleaf (needled) evergreens such as pines, junipers and yews; (2) broadleaf evergreens such as rhododendrons, hollies and boxwood. The narrowleaf evergreens generally grow more rapidly than broadleaf evergreens, include many tree forms, and are commonly grown only for their foliage. Broadleaf evergreens include many shrub forms and are often grown for flowers and fruit as well as for foliage.
Limit the pruning of most evergreens to the removal of dead, diseased, and mechanically injured wood and maintaining the natural shape of the plants. Formal effectssuch as clipped hedges, topiary, and espaliers require regular attention and special equipment.
When to Prune
Dead, diseased, and broken wood can be removed at any time of year. The best time for general pruning is in late winter or early spring, immediately before growth resumes. Narrowleaf evergreens may be pruned a second time in June before new growth has matured. It may be necessary to give particularly fast-growing plants an additional light pruning or two during the growing season. Good judgment must be exercised when pruning flowering evergreens, such as hollies, to avoid drastically reducing the amount of next season's flowering wood so any pruning should be done as soon after flowering as possible. Severe pruning can usually be avoided if pruning is done annually.
How to Prune
It is important to have the necessary tools in proper working order for pruning. These tools include a hand pruner, lopping shears, hedge shears, and a curved pruning saw.
Narrowleaf evergreens are characterized by growth that is either whorled or random (non-whorled). When pruning narrowleaf evergreens, such as pines, make cuts just above the needle whorls. Most new lateral growth is stimulated at these points rather than along the stems between the whorls.
In pruning most other narrowleaf and broadleaf evergreens, cuts can be made at any point along the branch, but care should be taken not to cut too far back into the older wood, because new growth is not as readily produced from such wood. When selectively pruning, it is a good practice to cut the growth back to a side shoot. Some evergreen species, such as Japanese yew, boxwood, and evergreen privet, withstand relatively heavy pruning. These plants can be sheared, which involves the uniform removal of new growth to make a plant conform to a prescribed shape. Because shearing encourages the formation of additional lateral growth, a more dense habit of growth is created. The amount and manner of pruning depend to a large extent on the type of plant, its location, and the particular tastes of the gardener.
Pointers for Specific Plants
Pines: Prune pines in early spring. Make cuts just above needle whorls. Additional pruning may be done before new growth hardens in June. Pines normally require little pruning.
Spruces and Firs: Cuts may be made at any point along the younger portions of the branches. The best time to prune spruces and firs is in the early spring. Pruning is necessary to maintain the natural shape of the plants.
Juniper, Camaecyparis and Arborvitae: This group consists of many tree, shrub, and prostrate forms. These species can withstand relatively heavy pruning and many may be trained into various forms by shearing. Early spring pruning is best, but additional light pruning later in the season may be necessary.
Yew and Hemlock: It is preferable to allow these plants to retain their natural form, but both respond well to heavy pruning and shearing. Yews are able to withstand exceptionally severe pruning into the older wood. Early spring is the best time for pruning, although occasional light pruning later in the season may be necessary.
Rhododendron, Azalea, Pieris, and Mountain Laurel: These plants generally require very little pruning because they are slow growing. Old flower clusters should be removed immediately after flowering. Prune out only dead, diseased, weak, or wayward branches.
Boxwood, Evergreen Privet, Barberry, and Pyracantha: With the exception of boxwood, these species grow rather rapidly. All these plants will stand heavy pruning, which is best done in early spring. Because they are generally quite vigorous, additional trimming during the growing season may be advisable.
Hollies: These plants include both tree and shrub forms. American holly may be pruned in December for Christmas greens. Chinese holly is also a source of attractive greens and may be trimmed in the early spring. When pruning American holly, always make the cut at a node, just above a lateral bud. Prune so as to maintain the natural shape of the tree. The shrubby Chinese and Japanese hollies can be more severely pruned and may require some additional light pruning during the growing season.
Mahonia and Leucothoe: These are rather slow-growing plants which require little annual pruning. If pruning is necessary it should be done immediately after these plants flower in the spring.
Adapted from Delaware Cooperative Extension, 2000
Useful Websites
A Guide to Successful Pruning, Pruning Evergreen Trees (Virginia Cooperative Extension)
http://www.ext.vt.edu/pubs/nursery/430-457/430-457.html
Pruning Evergreen Shrubs (Virginia Cooperative Extension)
http://www.ext.vt.edu/departments/envirohort/factsheets2/shrubs/feb88pr2...
Pruning Evergreens (Purdue Extension)
http://www.hort.purdue.edu/ext/evergreens.html
Pruning Evergreens in the Landscape (University of New Hampshire Cooperative Extension)
