Most homeowners know that the best time to prune deciduous trees is during the dormant season, from late November to March. But many are unsure when is the best time to prune evergreens, like pine, spruce and juniper.
Dead, Damaged or Broken Branches
Evergreens can be pruned at any time of year if the objective is to remove entire branches. This is usually done when branches or limbs are damaged, broken or becoming obstructions. When removing entire branches, pruning cuts should not be made flush with the trunk, but outside the swelling at the base of the branch called the branch collar.
The optimum time for pruning, when the objective is to trim or shape an evergreen tree, often depends on when the evergreen plant puts on its new growth for the year, often a short 3-4 week period in early spring. Pruning at this time of year will cause the plant to become bushier and fuller.
Keep in mind that only 1/3 of the new growth should be removed at one time. Cuts can be made at any location on the branch that contains green foliage. Refer to March- A Great Time for Pruning, for more specifics on how to make pruning cuts.
Never make pruning cuts behind the green foliage on a branch. Bare wood will seldom form new buds and the stubs will die without producing new foliage.
Pines are pruned differently. Pines produce a cluster of buds only at the end of the current season's growth. Therefore, pruning cuts on pines should be made on the current season's growth or the new candles, after the shoots have fully elongated. Mid-June to mid-July is a good rule of thumb for pruning pines, although there may be deviations due to growth characteristics of individual pine species and variations in annual weather.
If pines are pruned too early, too many buds may form, resulting in many weak branches in the next growing season. Pruning too late may not allow enough time for buds to form before hardening off in the fall. Pruning into 2-year-old wood or last year's growth delay bud formation for a year.
Yew, Spruce & Fir
Pruning yew, spruce and fir is not as critical. They produce new buds all along the new shoots through the growing season. The optimum time for pruning spruce and fir is between April and August after the buds have formed. Restrict pruning to current season's growth.
Juniper, Cedar & Arborvitae
Evergreen with scale-like leaves such as junipers, cedars and arborvitae may be pruned at any time of year, but early spring is preferred so that fresh pruning cuts are quickly covered by new growth.