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Proper Pruning

A Cut Above the Rest

You're stumped about the mystery of pruning. It doesn't seem like the street trees ever get pruned. The trees on your street look overgrown, have broken branches, or are hanging down into traffic. The following information should clear up any confusion you may have about when, why, how and who should prune trees.

Trees are living beings that require proper care in order to grow and thrive in the city. When wronged by ignorance, trees live damaged, and ultimately shortened, lives and can even become hazardous. But by understanding proper pruning, you can contribute to the good health of Claremont's community forest.

The International Society of Arboriculture (ISA) is a highly respected organization of professionals dedicated to, and trained in, quality tree care. The City of Claremont follows ISA guidelines in all avenues of tree planting and care - especially pruning. The Community Services Department maintains a highly trained Forestry Maintenance Crew. Our City uses an ISA Certified Arborist, and our contracted crews are required to have at least one certified supervisor oversee all tree work.

To keep mature trees safe and healthy, the dead, dying, broken or diseased limbs are removed and "sucker" growth sprouting from the base of the tree is cut away. Crossing or weakly attached limbs may also be removed to maintain a strong branch structure. Some foliage is removed to lighten the ends of branches and let light into the dense canopies. Taking into consideration a tree's growth rate, ISA guidelines state that no more than 25% of a tree's living branches and foliage should ever be eliminated.

In other words, slow growing species should be pruned no more than 10%, while faster growing varieties can handle up to 25%. Young urban trees have unique pruning needs, and our City staff keeps careful track of each new tree to insure it receives proper care. And a well-pruned tree should always have a natural shape.

Frequency of pruning is also important to a tree's health. Based on their growth patterns, City street trees are generally placed in one of three cycles for pruning:

  • Low (every nine years),
  • Medium (every six years), or
  • High (every three years).

Citizen requests for tree pruning can be made to the Community Services Department, (909) 399-5431. City staff will inspect each tree and grant or deny a request based on the needs of the tree (as detailed in the criteria listed above) and public safety concerns. If you wish to do additional work beyond what the City provides, you may obtain a permit to have your tree pruned to City standards by a private arborist.

Natural Target Pruning

When urban trees enjoy good health, their natural systems control decay from pests and disease. Proper pruning goes a long way towards promoting this process. Claremont uses Natural Target Pruning to care for its trees. You can also use this process for pruning your own trees. Here is how Natural Target Pruning works:

  • First, find the branch collar (the bulge or wrinkle where the branch meets the trunk).
  • Next, cut the limb just outside the collar. If the branch is large or heavy it's best to remove it in smaller sections. Make an undercut (see diagram) before making the final cut to prevent bark from tearing. Eliminating the excess weight will make the final cut much easier and reduce the risk of damaging the tree.
  • Make the final cut, being certain to keep it smooth. Cutting this way allows the wound to callous over properly and for the tree to begin its natural line of defense against pests and disease. Leaving stubs or cutting inside the collar compromises the tree's natural ability to control decay which can structurally weaken the tree and make it unsafe.


Despite what is often accepted as common practice, the tops of trees should NEVER EVER be cut off! Commonly referred to as "topping," this drastic procedure is deadly. The uninformed will point to a topped tree's profuse display of dense new growth as proof that no serious damage was done. "It all grows back," they say. Sometimes it does - but along with the regrowth, topped trees must also battle severe health and structural problems.

When a tree is topped, massive amounts of live growth are violently lacerated from it. Cuts are often quickly and carelessly made. Stubs usually remain. Because its source of food has been so radically diminished, the tree must call on its reserves of stored energy to put out new growth. This dense output of greenery is weakly attached and makes the tree highly unstable particularly in windy or stormy weather.

Persistent topping is a virtual death warrant to a tree, forcing it to constantly deplete its stored energy. It eventually becomes so weak that any adverse condition, such as drought or pest infection, will kill it. Topping of street trees is forbidden in the City of Claremont.

Options to topping do exist, depending on the situation and your particular needs. Here are a few alternatives:

  • Crown Reduction. Also known as "drop crotching", crown reduction allows you to decrease the tree's height while retaining its natural shape; useful if your tree is growing into an overhead obstacle such as a more dominant tree. For overhead power line clearance, please contact your local utility company.
  • Thinning. This is the reduction in a crown's density by removing some limbs in the top and around the periphery of the canopy, as well as branches along the trunk, to create more space and newer growth. This process is helpful in reducing the hazards of wind damage.
  • Windowing. A less intensive form of thinning, involving the removal of branches in specific parts of the tree; great for helping you maintain that beautiful view of the mountains behind your house, without sacrificing your beautiful tree!

Call the Community Services Department, at (909) 399-5431 if you:

  • Witness a City tree being improperly pruned
  • Have any questions about the pruning of City trees
  • Want to request that a City tree be pruned
  • Know of a tree that has suffered storm damage
  • Have an interest in learning how to prune and maintain a City tree yourself
  • Want more information about caring for your privately-owned trees
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