Can You Trim an Evergreen in Zero Degree Weather?

General Guidelines for Pruning

• The best time for pruning to trim or shape an evergreen depends on when that tree or shrub puts on new growth for the year. Pruning an evergreen in what is typically a three- to four-week period of growth in early spring causes the plant to become fuller and bushier.

Spring Pruning

• Douglas fir (Pseudotsuga menziesii), which is hardy in U.S. Department of Agriculture (USDA) plant hardiness zones 4 through 6, fir (Abies spp.), also hardy in USDA zones 4 through 6, and spruce (Picea spp.), hardy in USDA zones 2 through 8, grow in spring from buds on the tips of branches, called terminal buds. In order to maintain one of these evergreen tree's natural shape but promote denser growth, prune the branch tips back to a bud growing laterally. An option is to remove two-thirds of an unbranched tip to keep the tree fuller in that location.

Late Spring, Early Summer Pruning

• Dormant buds are farther back on the stems of yews (Taxus spp.), hardy in USDA zones 4 through 7, hemlocks (Tsuga spp.) and arborvitaes (Thuja spp.) than they are in some other evergreens. Prune a Canadian hemlock (Tsuga canadensis), hardy in USDA zones 3 through 7, in late spring or early summer after its new growth appears. If you want new growth to mask your pruning cuts in an American arborvitae (Thuja occidentalis), hardy in USDA zones 2 through 7, then prune it in early spring. Encourage compact growth by pruning branches back to a branch or bud. Pine trees (Pinus spp.) grow clusters of buds on the tips of new growth. The best time to prune pines is from mid-June to mid-July. They are hardy USDA zones 3 through 9, depending on the species.

False Cypress and Juniper Pruning

• Evergreens in the genus Chamaecyparis, sometimes called false cypress, and junipers (Juniperus spp.) need little pruning other the tips of their awl-like foliage in summer. Examples of such evergreens include the widely planted Hinoki cypress (Chamaecyparis obtusa), which is hardy in USDA zones 4 through 8, and the common juniper cultivar "Effusa" (Juniperus communis "Effusa"), hardy in USDA zones 2 through 7. Do not prune these plants after midsummer because their new growth will not have the chance to harden before winter. They should not be pruned back to their older areas that do not have leaves because it will take years for new growth to conceal the pruning cuts.