Pruning that helps the tree
Good pruning improves a tree's structure, health and safety without harming it. Poor pruning, especially "topping," does the opposite. Understanding the difference helps you hire well.
Good pruning practices include:
- Removing dead, diseased and broken branches (often called deadwooding).
- Structural pruning of young trees to develop a strong central leader and well-spaced branches.
- Thinning selected branches to reduce weight on long limbs and let light and air through, without stripping the interior.
- Clearance pruning to keep branches off roofs, chimneys, walkways and driveways.
- Reduction cuts that shorten a limb back to a smaller branch that can take over, rather than leaving a stub.
Practices to avoid:
- Topping: cutting main stems back to stubs. Topped trees produce weak, fast-growing sprouts, decay at the cuts, and often become more hazardous than before.
- Lion-tailing: stripping the inner branches and leaving foliage only at the ends, which overloads limbs.
- Removing too much at once. Taking off a large share of a tree's live canopy in one visit stresses it.
- Climbing spikes on trees that aren't being removed. Spikes wound the bark.
- Flush cuts and stubs. Proper cuts are made just outside the branch collar, the slight swelling where a branch meets the trunk.
Hazard care
Some trees have defects that raise the risk of failure. An arborist can assess the tree and recommend measures such as:
- Removing or reducing specific high-risk limbs over houses, driveways and play areas.
- Cabling and bracing, where steel cables or rods support weak branch unions or split trunks.
- Lightning protection for valuable trees in exposed locations.
- Monitoring trees with defects that aren't urgent but should be checked periodically.
Warning signs include cracks in the trunk or main limbs, a weak V-shaped union between two main stems, large dead branches, mushrooms or conks at the base, cavities, and a sudden lean.
When to prune
Many trees are best pruned when dormant, in late fall or winter, when it's easier to see the structure and the risk of spreading some diseases is lower. Dead, broken and hazardous branches can be removed any time. Some species have specific timing recommendations to avoid pests or bleeding sap; a knowledgeable arborist will know them for your trees.
Clearance around homes
Branches touching the roof scrape shingles and give pests a path into the house. Branches over the roof drop leaves into gutters. Keeping a clearance between branches and the house, and between trees and chimneys, reduces maintenance and fire risk. In fire-prone areas, local guidelines may recommend specific clearances around structures.
Questions to ask
- What will you remove, and why?
- Do you follow recognized pruning standards, and will you avoid topping?
- Will you use climbing spikes on this tree? (They shouldn't on a tree that's staying.)
- How much of the canopy will you remove?
- Does anyone on your crew hold an arborist credential, such as ISA arborist certification? Ask to see it.
Young trees
The best time to shape a tree is when it's young. Light structural pruning in the first several years after planting, removing competing leaders, crossing branches and branches with weak, narrow unions, sets up a strong framework that needs far less corrective work later. It's also far cheaper than trying to fix a mature tree with poor structure.