The term evergreen commonly conjures a mental image of juniper or pine trees with needlelike foliage. However, this plant type also encompasses flowering shrubs such as azaleas and hollies. These are known as needle and broadleaf evergreens, respectively, and are pruned somewhat differently based on their growth habits, according to Purdue University. The state of Iowa is covered by USDA zones 4b through 5b meaning winter temperatures can drop as low as minus 25 degrees F. Pruning should generally be conducted in the fall or early winter before the first snowfall. Light annual pruning is optimal but more substantial pruning on a three-year cycle is tolerated, when necessary.
Thin the branches of your needle evergreens, if needed, and refrain from cutting just the branch tips. Never remove large structural branches and limbs, as these cannot usually be regenerated even over long periods of time. Always stop short of removing old wood with little or no foliage. Remove branches evenly throughout the shrub or tree and never take out more than one-third of the total foliage and woody tissues, in order to prevent a shock response.
Prune broadleaf evergreens by thinning and by trimming the branch tips that extend far beyond the main body of the shrub, if desired, to maintain a tidy look. Cut branch by branch and follow the contours of the evergreen to preserve its natural form. Thin older branches back to the main trunk or crown of the plant to encourage new branch growth. Remove up to one-third of the old wood each year if needed or desired, but no more.
Follow exceptions to fall pruning for flowering or berry-producing broadleaf evergreens such as azaleas and holly. Flowering evergreens can be groomed during the blooming season to remove the spent flower heads thereby encouraging reblooming. Cut back the flower head on the stem on the bias, just 1/4 inch above a pair of leaves. Prune your holly shrubs in the winter when the decorative red or white berries are mature and plant cuttings are harvested for holiday decor. Earlier pruning will diminish or destroy the decorative berry crop.