There are many objectives of tree pruning in the urban landscape. The foremost objective is to prolong the functional life expectancy of trees. However, it also allows for an aesthetically pleasing look in neighborhoods, communities and commercial properties.
Research has proven the importance of proper pruning versus improper pruning. Proper pruning creates strong tree structure that allows trees to flourish in their environment, whereas improper pruning can be detrimental to the lifespan, health and safety of a tree.
Reasons for pruning
- Improve overall structure: pruning for structure creates a strong tree that requires less maintenance as it matures and is less susceptible to failure or storm damage.
- Thin appropriately: remove crossing or interfering branches and reduce codominance. Improved branch spacing lets sunlight reach the interior and promotes airflow, reducing storm-related failure.
- Promote clearance: trees near buildings, sidewalks, streets and power lines can be pruned to provide adequate clearance.
- Remove dead, dying, diseased and broken branches: this promotes healthy growth and eliminates sites that encourage insect breeding, decay and disease.
- Reduce long, heavy branches: with Colorado's wet, heavy snows, minimizing branch failure potential matters.
- Mitigate risk: neglected mature trees can pose serious hazards to people, homes and power lines.
- Promote flower and fruit production: incorrect pruning on flowering and fruiting trees slows production and increases disease susceptibility.
When is the best time to prune?
The best time to prune is now — it's never too late or too soon to prune your trees. There are exceptions. Certain species such as crabapple, apple, pear, hawthorn, mountain ash and American elm should be pruned in the dormant season, when they are less susceptible to diseases such as fire blight.
| Window | Best suited to | Why |
|---|---|---|
| Dormant season (Nov–Mar) | Crabapple, apple, pear, hawthorn, mountain ash, American elm | Fire blight and Dutch elm disease vectors are inactive; structure is fully visible with the canopy off |
| Late spring to summer | Most established shade trees, clearance and deadwood work | Wounds close quickly during active growth; live crown response is easy to judge |
| Any time | Dead, broken, hazardous or storm-damaged limbs | Risk reduction is never deferred for seasonal preference |
| Avoid | Heavy reduction during drought stress or extreme heat | Removing live crown while a tree is already water-stressed compounds the stress |
Cut quality and the ANSI A300 standard
Great Western prunes to ANSI A300 standards on every job. In practice that governs where the cut lands and how much live crown leaves the tree. Cuts are made just outside the branch collar so the tree can compartmentalize the wound with its own defense tissue — flush cuts remove that collar and leave a wound the tree cannot close, while stub cuts leave dead wood that decays back into the trunk.
- Cut outside the branch collar and branch bark ridge. No flush cuts, no stubs.
- Use a three-cut method on limbs heavy enough to tear bark down the trunk.
- Keep live crown removal modest on any single visit — mature trees tolerate far less than young ones.
- Never use climbing spikes on a tree that is being pruned rather than removed.
- No wound paint. Dressings trap moisture and slow natural compartmentalization.
Why topping is not pruning
Topping — cutting large limbs back to indiscriminate stubs to reduce height — remains the most damaging practice performed on Colorado landscape trees. The tree responds with dense epicormic sprouts that are weakly attached to the outside of the decaying stub. Within a decade those sprouts are heavy, poorly anchored and far more failure-prone than the original limbs. Many multi-leader trees now requiring cabling across the metro were topped years earlier.