• To remove broken, damaged, insect-infested or diseased branches.
• To reshape or improve the branching structure.
• To thin out the branching structure to renew or invigorate the plant.
• To promote flower and fruit production.
• To rejuvenate older shrubs or evergreens.
• To remove water sprouts or suckers at the base of the plant.
• To protect people or property, such as near overhead wires, blocking street lights or street signs, low branches where mowing, or branches overhanging on the roof.
• The proper tool is essential for proper pruning.
• Types of pruning tools include:
- Hand pruners (by-pass or anvil-type).
- Shears (lopping or hedge).
- Saws (bow or pruning).
The natural form of an evergreen is the most desirable, and pruning should be limited to correcting growth defects or maintaining the natural form unless it is being used as a hedge.
Evergreens that grow continuously throughout the growing season may be pruned at almost any time. However, do not prune after July 15th as this may encourage growth too late in the growing season and the plant will be more susceptible to winter injury. Junipers, Arborvitae, Yews and Hemlock are evergreens that grow continuously.
Pines, Fir and Spruce put on a single flush of growth in spring/early summer and then stop growing for the season. These evergreens must be pruned before the new growth (called candles) is fully expanded.
Pruning is best done in early to mid June when the candles are about three-fourths elongated. If done too late, the result is dead stubs. Remove no more than one-half of the new growth for best results.
Proper timing is crucial for flowering shrubs. Shrubs that bloom early in the growing season on old wood should be pruned immediately after flowering in order not to prune off flower buds. These include: Rhododendrons and Azaleas, Chokeberries and Chokecherries, Forsythias, Juneberries or Serviceberries, Magnolias, Flowering Plums and Cherries, Lilacs, and early blooming Spireas. Any winter injury may be removed as soon as the plant comes into leaf.
Shrubs that bloom late but on old wood should be pruned either first thing in the spring or immediately after blooming. Shrubs included are: Mockoranges, Potentillas, Shrub Roses, and Weigelas.
Shrubs grown primarily for their foliage, fruit or other reasons should be pruned in the spring before new growth begins. Any winter injury may be removed once the plant leafs out. These include: Barberries, Viburnums, Dogwoods, Euonymuses, Ninebarks, Alpine Currants, Winterberries, Snowberries, Honeysuckles, Sumacs, and Sand Cherries.
Most summer flowering shrubs bloom on new wood and should be pruned first thing in the spring. Shrubs included in this category are: most Spireas, Hydrangeas and Clematis.
As with the evergreens, avoid pruning shrubs after July 15th as the new growth, and the entire plant, may be more susceptible to winter injury.
It is necessary to prune at the proper time for some trees that are susceptible to disease or insect infections. Oaks should be pruned during December, January or February to minimize the spread of oak wilt infection. If pruning during the summer because of storm damage, cover immediately with a wound dressing.
Apples, Flowering Crabapples, Pears, Mountain Ash, and Hawthorns should be pruned when dormant to minimize the spread and chance of infection by a bacterial disease called fire blight. Some trees will “bleed” (the sap flows freely) if pruned in late winter or early spring. Although this does not harm the tree, it can cause major concern for many homeowners.
All Maples, Honey locusts, Butternuts and Walnuts, Birch, Ironwood, Blue Beech and Elm should be pruned when they are actively growing to prevent “bleeding”. Early summer is best. Prune Honey locusts during dry spells.
NOTE: To help protect against sunscald on young trees or thin-barked species, use a commercial tree wrap in fall to wrap from the base of the tree up to the first major branch. Using a porous wrap will protect the tree while still allowing the passage of gases and liquid through the material. Always remove the wrap in the spring. Never leave it on through the growing season or you will put the tree at risk of disease. Thin-barked trees such as Maples, fruit trees and Honey locusts may require wrapping for several winters to prevent the occurrence of sunscald.