Thinning A Tree Canopy: Benefits And Method

Posted on: 12 March 2015

Overgrown trees may look fine from the ground, but the interior is a ticking time bomb of future problems. Deciduous trees require thinning more often than most evergreens, generally every two to three years once the trees reach maturity. Understanding the benefits of thinning along with the proper method helps you make the best pruning choices for your landscape trees.

Benefits of Thinning

  • Sunlight. When the canopy of a tree becomes overgrown, sunlight can't reach the interior branches and leaves. This leads to weak foliage and branches that are more prone to pests and diseases. Proper sunlight penetration allows the branches to increase in diameter, resulting in a stronger, healthier tree.

  • Air circulation. Poor air circulation is one of the most common reasons for disease – especially fungal diseases. Airflow around branches and leaves dries excess moisture on the leaf and wood surfaces, which prevents fungus and disease organisms from growing.

  • Wind damage prevention. Allowing airflow also prevents wind damage. Breezes pass through and around the branches instead of forcing them to break.

  • Bark protection. Over-crowded tree canopies result in crossed branches, which rub together. This rubbing action wears down the branches and weakens them, leaving them susceptible to disease and insect penetration, while also making them more likely to break.

Basic Thinning Method

Thinning requires two main tools, a pruning saw and bypass shears. You will also need a bucket containing one part bleach to nine parts water. After each cut, especially those made through diseased or dead wood, rinse the pruning tools in the bleach solution to sanitize them.

When thinning the tree, begin by removing any dead or damaged branches. Cut these back to the nearest healthy branch or to the trunk. Then, cut out the small branch tips back to where they are 1- to 3-inches wide. Use the shears for branches less than 1 inch in diameter and the saw for thicker branches.

Finish up by trimming out any interior branches that are crossed and rubbing together. It's also a good idea to remove waterspouts at this time. A waterspout is a branch growing straight up, completely vertical to the main branch its sprouting from. You can usually remove up to a third of the tree's canopy without causing the plant any stress.

You can usually prune smaller trees yourself if you can easily access the canopy with a step ladder. Larger trees may require better equipment to access the upper branches and interior, especially for safety, so these are often better left to professional tree trimmers.