Why Prune?

• To rejuvenate sickly plants.
• To assist in control of insect pests, fungal diseases (i.e. borers, side branch dieback in Cornus, etc.).
• To correct faulty habits. (Note: best done in "formative" years of development.)
• To promote correct or interesting branch formation (i.e. pollarding).
• Bring about earlier blossoming.
• To complete removal of dead and dying branches.

Pruning Principles

• Severe pruning when the plant is dormant stimulates the production of strong, leafy shoots. Pruning when plant is actively growing tends to check exuberant growth and help bring about formation of blossom buds.
• Trees and shrubs which blossom early, ordinarily should be pruned immediately after they flower, while plants which bloom in summer or autumn (on current season's growth) can be pruned in early spring.
• Maintain a natural habit.
• Pinching back stimulates branching and compact habit.
• Leave no stubs; cuts should be made close to the supporting branch or trunk, or just above a bud-preferably one pointed in the right direction. Avoid flat cuts that will catch snow and ice. On trees and large shrubs make cuts close to, but beyond the branch bark ridge (shoulder rings) and the collar at the base of a branch. (Note: collars may extend further-particularly on a weak or dead branch.)
• The branch-bark-ridge zone is usually a strong, physical barrier to decay between the lateral branch and it's "mother" branch. Callus tissue promoting auxins are found within this zone.

Helpful Hints

• Know the plant you intend to prune (its family, range, hardiness, habitat, native counterparts). Know its habit and ultimate size in your hardiness zone; cultural requirements; and site considerations (drainage, soil type, competition, light requirements, etc.).
• Do not paint cuts or wounds of any size.
• Do not prune newly planted trees (growth promoting auxin in apical meristematic tissues).
• The time of year to prune is largely dependent upon your reason to prune. Rejuvenation pruning is best done just before the onset of growth in spring. Structural or corrective pruning is best accomplished during the growing season, as sucker growth will be reduced. Do not prune maples and birch during sap flow.
• Callous tissue will not form when the plant is dormant; therefore limit major pruning during the dormant season (also freezing of newly cut branches can result in significant tissue damage, leaving a vectors for insect and/or diseases).
• Fast growing deciduous shrubs (i.e. forsythia, lilacs, red-osier and shrub dogwoods, honeysuckle, etc.) should be pruned annually for best results. Remove dead and diseased wood as well as 10-20% of older branches at ground level. (Note: that 15% removal annually will result in an 8 inch tall lilac; 30% results in a 5 foot tall lilac). Periodic pruning will rejuvenate shrubs. Slower growing shrubs (viburnums, witch hazels) should be pruned less frequently (approx. 5 years).
  Shrubs to be pruned annually in spring just after flowering:
  Shrub dogwoods, deutzias, forsythia, mock oranges, spiraeas, lilacs, weigelas, hypericums.
  Early spring pruning for shrubs which flower on current year's growth:
  Buddleias, clethra, hibiscus, viburnums.
• Narrow-leaved evergreen shrubs (yews, junipers, etc.) should be pruned during late June and July (no later than mid-August), and may be "formally" pruned.
• Evergreen trees and shrubs pruning varies with different genera. Pines lack adventitious buds capable of generating suckers. Top pruning of pines (shearing) best done in late June when new growth is in the "candle" stage prior to bud set (pine buds form only once a year, unlike spruce and fir, in the new candle. Therefore pruning for shape must be confined to current year's growth. Shearing generally involves removal of about ½ the candle.
• Pruning of spruce and fir is best done in late March to early April. Apical dominance is important, so prune just above a strong bud.
• Pruning a deciduous shade tree:
  Pruning should be done when the tree is young, periodically thereafter. The main scaffolds should be spaced vertically along and radially around the trunks. When young leave "temporary" branches along and below the main scaffold branches. "Temporary" branches increase trunk caliper and taper; shade the trunk; and reduce the likelihood of damage. Prune temporaries as not to interfere with pedestrian traffic, and not to compete with scaffold branches. At each dormant pruning the largest temporary branches should be pruned. Reduce the number of temporaries over the years.
  Prune for crown configuration: Two reasons to prune for proper crown configuration is to develop a strong, tapered trunk; and, to distribute stress all along the trunk in high winds. The ideal branch configuration would center wind loads acting on the tree at about 2/3 of the total height. To do this greater than 50% of the foliage should be on branches originating on the lower 2/3 of the trunk. Less than 50% should originate on the upper 1/3 of the branches.
• Use the "right tool for the job" when it comes to selecting a pruning tool. Keep them sharp and sanitize tool between specimens using isopropyl alcohol.

Resources:
Tools: A.M. Leonard 1-800-543-8955 www.amleo.com
Biostimulants: Plant Health Care, Inc. 1-800-421-9051 www.planthealthcare.com