Learn how and when to prune common woody landscape plants to improve health and productivity, and to enhance their beauty.
Review of Pruning Basics
- Goals/reasons to prune
- Tools, Terms, Techniques
- Timing: Most often done during dormant season (November–March)
- Know when to call the professionals: Colliers Arbor Care, Arbor Pro, Halsteads, Honl Tree Care
Pruning of Young Trees
Pruning newly planted trees should be limited to removal of dead/broken branches. All other pruning should wait until the 2nd or 3rd year when tree has recovered from planting.
- Always have a pruning goal and know plant’s natural shape/habit
- Smaller cuts do less damage (less than 2-inch diameter)
Making the Cut
Prune to the lateral bud that will produce the branch you want. The placement of that bud on the stem points in the direction of the new branch. An outside bud, pruned with a slanting cut just above the bud, will usually produce an outside branch. A flat cut above the bud allows two lower buds to release and grow. Cut just outside of the branch collar to allow the tree to heal and reduce spread of decay.
Primary Structure (Scaffold)
The goal is to promote a strong central trunk and leader with sturdy, well-spaced branches.
- Trunk development and raising: Trees grow from the top, not the bottom; maintain a strong central leader and never top a tree!
- Co-dominant stems create a struggle for apical dominance and should be resolved by selecting one leader and shortening the other back to the main trunk or a bud while the tree is young (new leader may need to be staked or supported to be straight while young and flexible).
- Secondary branches contribute to stability and a well-tapered trunk. When raising the canopy, it is best done gradually to promote proper trunk diameter growth. When removing lower branches, maintain at least ½ of the foliage in the lower ⅔ of the tree; the lowest branch should originate in the bottom ⅓ of the tree’s height. Remove before branch diameter exceeds 2 inches.
- Some trees naturally grow low to the ground; only raise canopy if clearance is necessary.
- Excessive removal of lower branches increases potential for failure by decreasing trunk taper, causing cracks/decay, and transferring weight to the top of the tree.
Pruning Mature Shade Trees
The basic types of pruning done on mature trees are reduction, cleaning, thinning, and restoration.
Reduction: Removing a smaller diameter branch/trunk back to a larger one. In reduction cuts, the side branch removed must be at least ⅓ the diameter of the parent branch or it is a heading cut. Heading cuts tend to release waterspout/sucker growth, which is weak and should be avoided. Example: Remove a 1-inch diameter branch back to a 3-inch diameter branch. Recent research is questioning the effectiveness of tree reduction as it often regrows within a few years. Not all trees can be reduced without predisposing it to death or decline. Ideally, trees are selected with adequate space for them to attain their mature size with minimal pruning. Just because a tree is tall does not indicate that it is structurally unsound. Always remember to balance your pruning budget and remove no more than 20-25% of total growth. Slower growing or more mature trees often have a smaller budget of 5-10%.
Cleaning: Removal of dead, diseased, cracked, and broken branches; most middle age/mature tree pruning is cleaning. Removal of dead wood does not count against pruning budget and can be done at any time of year. Even when removing dead wood, maintain branch collar integrity and do not attempt to make cuts flush with trunk/branch.
Thinning: The selective removal of smaller branches (parallels) no larger than ½-inch to 2.5-inch diameter; often done to retain crown shape/size, not to reduce in height. Usually, focus is on upper/outer canopy areas; often regrows after a few years. This type of pruning can help reduce snow/wind damage, but is often best done by a professional arborist and can be quite expensive. Avoid lion-tailing—do not remove all live, small growth from the tree’s interior; this decreases the tree’s vigor and shifts more weight to outer canopy, creating more vulnerability to wind, snow, and ice damage.
Restoration: The selective removal of branches, sprouts, and stubs from trees that have been damaged by improper pruning, vandalism, or storms; generally requires several years of annual pruning to recover. When dealing with excessive watersprouts, a rule of thumb is to remove ⅓ and reduce ⅓ with each annual pruning. Removing all at once often stimulates more to grow.
Plants that tend to easily grow watersprouts (so only lightly thin): Cotoneaster, Hamamelis, Cherry, Crabapple, Filbert, Fig, Parrotia, Lilac, Magnolia, Plum, Dogwood
Shrubs tolerant of arborizing: Camellia, Laurel, Strawberry Tree, Rhododendron, Privet, Panicle Hydrangeas, Crepe Myrtle, Smoke Bush, Privet, Rose of Sharon
Specific Pruning Details on Popular Plants
- Hydrangeas: Covered in previous blog (Pruning 101)
- Lace-leaf and upright Japanese Maples
- Fruit trees: Most pruning should be done once we are past typical freezing weather, but before tree is in full bloom; light pruning and fruit thinning may be done in late spring or summer. Regular, annual pruning is better than waiting to do major repairs or restoration on neglected trees.
- Blueberries: Best done December–March, while dormant
- Home Orchard Society: www.homeorchardsociety.org
- Demonstration orchard on Clackamas Community College campus
- Plant Amnesty: www.plantamnesty.org
- OSU Extension Service: www.extension.oregonstate.edu
- OSU Master Gardener Program Training