The Rights, Wrongs, and Realities of Pruning

Andy Perleberg, WSU Extension Educator

Pruning is the most commonly implemented cultural practice among family forest owners. It helps produce lumber clear of knots, reduces the risk of fire climbing into crowns, may decrease the transmission of certain diseases, and improves the aesthetic appeal of the stand. Regardless of why you’re pruning your trees, it’s important that you do it and do it properly so your management objectives are achieved.

This article presents the basics of pruning. For a good “how-to” guide, try Conifer Pruning Basics for Family Forest Landowners (WSU 1984) or How to Prune Trees (USDA Forest Service 2012).

Why Prune?
close sawThe first step in pruning is answering the question, “What’s my ideal forest condition?” If you want a stand of crop trees with high quality wood, you’ll want to start pruning early in the tree’s life and conduct your pruning in combination with thinning treatments – typically when the tree diameter is about the size of a tuna can. If you prune before you thin, you risk investing time and money into pruning trees that will be removed in the future. As a general rule, you want to leave 50 percent of the total tree height in live crown. Reducing the crown beyond this level decreases the tree’s “energy factory,” or its ability to photosynthesize for maximum production and vigor.

Pruning to develop clear, knot-free wood is labor intensive and usually requires two or three prunings over time. It can be expensive to hire out the job as well, and there is no guarantee that the clear logs you produce will fetch a premium when they sell. Pruning certification does exist in New Zealand, but domestic markets don’t generally reward for this practice. If the market develops in the future, you’ll need documentation, so take photos and record your pruning activities in business or tree farm inspection records.

If your main reason for pruning is to reduce the risk of fire being carried into the crowns of the trees by ladder fuel, bear in mind that your goal is to reduce fuel and break the chain of radiant and convective heat. In this case, it is advisable to prune heavier and earlier in the stand’s development, achieving at least a 12-foot “lift” or clear bole. Because you should never remove more than one half of the crown at a time, you may need to prune the tree at least twice.

With the exception of fire protection, pruning is typically conducted before the limbs are greater than one inch in diameter. There is no need to dress the wound because the tree will seal off with pitch and eventually wood will compartmentalize the site, creating clear wood beyond that ring. Pruning early before the limbs are large in diameter decreases the opportunity for bugs and crud to enter, and will develop clear wood sooner. Never cut into the branch collar, as that will greatly enlarge the wound.

Finally, pruning can reduce infection and risk of exposure to white pine blister rust, a potentially deadly disease that can be contracted by all five-needled pines. The blister rust fungus enters the tree through the needles and travels down the branch where the symptoms are expressed by an orange-red canker on the trunk of the tree. It is practically impossible to eliminate blister rust from the stand, but pruning and/or thinning any signs of disease can greatly reduce the chance of trees becoming infected. For a complete article about white pine blister rust, read White Pine Blister Rust: Pruning Can Increase Survival. Pruning may also help control mistletoe, an endemic parasitic plant to all conifer species.

When Should I Prune?
Pruning can take place anytime you have a free hour from August to February. Trees should never be pruned when they are actively growing (about mid- March to mid-July) because the bark and branch collars are soft and easily stripped off. You can also time your pruning to take advantage of specialty markets such as Christmas greenery.

Accomplishing the Pruning
Pruning work can be done by the landowner or hired out. If you’re going to do it yourself, make a schedule and try to stick to it – life branch removalfrequently gets in the way! You can also hire the job out, but if you’re not using quality pruning crews with supervisors, make sure your help is trained and closely supervised. Except for fire protection purposes, you should never prune more trees per acre than you expect to have when you actually harvest.

While there is a variety of tools that can be used, most professionals agree that chainsaws are too awkward and fast for use in pruning. If you choose to use chainsaws or motorized pole pruners, make sure the operator always has two feet on the ground. Never operate a saw when fatigued.

Quality saws are essential, so buy the best that you can afford. Keep them in good shape by removing pitch daily and replacing blades. Remember, a dull saw just makes your work slower. Good hand pruning saws can be purchased for about $25, while good-quality 18-foot telescoping poles cost as much as $200. Purchasing your saws from a forestry supplier ensures that the equipment has been tested by forestry professionals. Safety equipment is also a must, and includes a hardhat with safety glasses or a screen, a long-sleeved shirt or coat, boots, gloves, and thick pants.

Andy Perleberg can be reached at 509-667-6540 or andyp@wsu.edu. Portions of this article were originally published in Northwest Woodlands in the fall of 2008.