Many factors must be considered when pruning any type of shrub or tree. Proper pruning technique is necessary, and is described further at Trees are Good. Identification of the plant, along with knowing it’s growth or habit, flowering schedule, and reason for pruning, is also imperative.
Pruning of dead, dying, or diseased limbs should be done at anytime. The 3 D’s! Many problems can be avoided if the problems are not allowed to spread throughout the tree or even to the neighboring trees.
When dealing with deciduous trees and shrubs, there are four types of pruning categories: inconspicuous blooming, early blooming, late blooming, and fruits.
- Inconspicuous blooming trees and shrubs should be pruned anytime during dormancy.
- Early blooming varieties need to be pruned right after the blooms are spent. This ensures that the blooms for next season are not trimmed off.
- Late blooming plants can be pruned during dormancy, as the blooms for the next season will develop over the next summer.
- Fruiting trees and shrubs should be pruned only during dormancy, and always very lightly (unless renovating). There are special techniques for woody fruit pruning as described at the University of Oregon Extension’s website.
Pruning of deciduous shrubs and trees should never be done in spring, as the buds are about to break. Also, pruning in the fall, before dormancy, could cause a flush of new growth that will be winter damaged.
Lastly, identify the “bleeders” (Norway maple, yellowwood, Betula spp.) which should be pruned in summer, late fall or winter, not during a time when sap is running (spring).
When choosing to prune an evergreen tree or shrub, identification, growth habits, and flowering schedules need to be recognized. Most evergreens tend to have an inner area to them called the “naked zone”. Whenever pruning an evergreen, knowledge of where the zone starts is necessary so over-pruning does not occur.
- Needle-leaf evergreens (yews, arborvitae) need to be pruned during dormancy.
- The broadleaf, evergreen (boxwood, holly) pruning schedule is exactly like the late blooming deciduous schedule.
- Pines, spruces, and firs need their candles (fresh growth) pinched back 1/3 to 1/2 during dormancy.
Knowing the identification, growth habit, and flowering schedule of a plant can prove valuable information when choosing the right pruning time.