Time to prune — with caution

February can be one of the best times to prune your trees, but proceed with caution. When done correctly, pruning can lengthen a tree's life, increase its value to the landscape, and minimize safety issues.

If improperly done, however — especially if trees are over-pruned or "topped" — pruning causes a host of structural and biological problems that lead to pests, decay, liability issues and a shorter lifespan for your tree.

Timing

Avoid pruning trees after their buds start to expand. Pruning during this period can stress trees badly and disrupt their growth.

The best time to prune most trees, especially deciduous trees (trees that lose their leaves in the fall), is late in the winter before their leaves form. In other words, now would be a good time.

No 'flush' cuts

Learn where and how to make cuts before picking up your shears. The secret to good pruning is understanding that branch wood is distinct from trunk wood. Cutting a tree's branches flush with the trunk robs the tree of natural chemicals it needs to close the wound, leading to decay in the tree. So, the guiding principle of good pruning is to cut the branch, not the branch collar.

What's a branch collar? Take a close look at the underside of the branch. Notice the slight swelling on the bottom of the branch just before it enters the trunk? This area is called the branch collar; take care not to cut into it. Also, use sharp tools and make clean cuts.

Young trees

By lightly pruning a tree while it's still young, you can take measures now to ensure your tree won't become a hazard later on. Also, generally speaking, small cuts do less damage than large cuts, another good reason to prune trees while they're young, instead of waiting.

Trees with a main stem or trunk that branches into a narrow fork often form a "V-crotch" with "included" (embedded) bark in it, a structurally weak part of the tree. Remove one of the branches or stems to create a strong control leader. You can do this by retaining the stronger, more vigorous, larger-crowned side, and removing the less desirable limb.

Mature trees

In older trees, one of your main pruning objectives is to reduce potential hazards by removing the dead wood, weakly attached limbs and broken branches. Just remember, removing live foliage from a mature tree should be done only for good reason. Even 25 percent of live foliage removed on mature trees is too much in many circumstances.

Don't 'top' your tree

Tree topping is the indiscriminate cutting back of tree branches to stubs. Many people mistakenly "top" trees because they grow into powerlines, block views or sunlight, or simply grow so large that they cause worry for the property owner. Without a protective "crown" of leaves and branches, a tree can't feed itself or protect its sensitive bark from damaging sun and heat. Topping weakens trees, leaves them vulnerable to insects and disease and shortens their life span. Don't do it.

More tips

This is just a brief, simplified summary of pruning advice. Some types of pruning — such as trees near or in contact with utility wires or jobs that require climbing — should be performed by a professional arborist.

For more information, see www.treesaregood.com/treecare/treecareinfo.aspx.

To find a certified arborist, check out the International Society of Arboriculture website at www.isa-arbor.com; follow the link to the "Consumer tree care website." This site has helpful information on all aspects of tree care.

Cynthia Orlando is a certified arborist with the Oregon Department of Forestry's Urban and Community Tree Program.

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