When pruning mature trees, there are many factors to keep in mind — from the ideal time to prune to the type of cut required to using the right tool for the job. To examine all of these aspects of proper pruning, Arbor Age recently spoke with Phil Rogers, marketing channel manager at Corona Clipper.
AA: When pruning mature trees, how important is it that the professional understand how the particular tree being pruned will respond to each cut?
Rogers: It is very important, because each cut that a professional makes has the potential to change a tree’s growth pattern and overall health. Removing a mature tree’s foliage can stress the tree and lessen its growth. However, we all realize that trees in urban landscapes will have to be pruned for safety and aesthetic reasons from time to time.
The key is to only prune mature trees when necessary, and, before pruning, to understand the unique biology of the tree species. For example, certain trees can contract diseases when pruned during a time that trees are emitting spores. The disease spores can enter the open “wound” caused by pruning. In this case, it’s better to wait to prune until after the active spore transmission period has passed.
AA: Does routine pruning improve the health of the tree?
Rogers: Yes, routine pruning — when done correctly — can improve the health of a tree. That said, it’s important to remember that improper pruning can be more harmful than not pruning a tree at all.
Pruning a tree correctly on a regular basis should be done to remove dead or diseased wood, as well as thinning particularly dense growth to let light and air reach the tree’s inner and lower branches. A tree that has sustained an injury, such as a lightning strike or the breaking of its branches following an ice storm, should be pruned to prevent disease-causing organisms from entering the damaged wood.
AA: When should tree care professionals prune mature trees; and, by the same token, when should they avoid pruning?
Rogers: The best time to prune a tree depends on several variables — the species of tree, the tree’s location, its overall health, when it blooms, and whether its flower buds form on new growth or only on older wood.
Late winter or early spring is the best time to prune the majority of trees. The exact timing depends upon your geographic location. A general rule of thumb is to wait until the days have begun to lengthen and warm, but trees are still dormant. This can be mid-February in southern regions, or late March in a more northern climate.
In late summer, you can prune certain shade trees, particularly those that can lose too much sap if pruned in the spring, like maples or birches. Late-summer pruning can also be a good way to encourage fruit trees to set more flower and fruit buds and fewer leaf and branch buds. However, this is a situation where location makes a difference. In the Deep South, you don’t want to prune a fruit tree in late summer because pruning can encourage a growth spurt that would cause the tree to be at risk for cold injury.
AA: What recommendations do you have for removing larger tree limbs?
Rogers: Always cut large limbs back to a live branch or to the main trunk. When dealing with a very large limb, reduce its overall length first by removing it in sections and then using multiple cuts to remove the limb completely.
Most branches have an obvious, sometimes wrinkled, swelling at their base. This is called the “bark collar,” an area where cell growth is abundant. Because of this cell growth, wound closure in this area occurs more quickly. When making your cut, follow these steps:
Step 1) Make an undercut at least 6 inches from the bark collar
Step 2) About an inch beyond that, remove the limb with a top cut.
Step 3) Finally, remove the remaining stub with one smooth cut from top to bottom, just outside the bark collar.
AA: Please explain the proper pruning cuts for mature trees.
Rogers: A thinning cut removes branches where they originate on the trunk. A reduction cut shortens a limb to a lateral branch that’s substantial enough to resume the growth of the pruned limb. These two types of cuts are used to remove weak, damaged or dead branches, decrease the length or weight of heavy limbs or reduce a tree’s overall height. Reduction cuts are placed so as to distribute ensuing growth throughout a tree and retain or enhance a tree’s natural shape.
A heading cut trims a branch back to a bud, or trims a branch or leader back to a small branch that’s not substantial enough to assume the pruned branch’s growth. Heading cuts should only be used when pollarding trees; they should not be used for topping trees — a practice that should never be used unless a tree is being removed. Topping compromises a tree’s overall health and appearance.
A stub cut is like a heading cut but is made indiscriminately to a point on a branch or leader where no bud or branch exists. A stub cut is typically used when a tree is topped. Topping should only be done to cut off sections of limbs during the complete removal of a tree.
AA: Please explain the various pruning techniques for mature trees.
Rogers: Cleaning is the removal of dead, dying, diseased, crowded, weakly-attached, and low-vigor branches from the crown of a tree.
Thinning involves selectively removing certain branches to increase the amount of light and air that can penetrate through the tree’s crown. Thinning is typically done to reduce the weight carried by heavier limbs and to maintain the tree’s natural shape.
Raising removes the lower branches from a tree in order to provide clearance for pedestrians, houses or other buildings, vehicle traffic, or simply, a better view.
Reduction pruning is often done to reduce the size of a tree to make room for utility lines. This task is best accomplished by pruning back the leaders and branch terminals to lateral branches that are large enough to assume the terminal roles (at least 1/3 the diameter of the cut stem). Compared to topping, this helps maintain the form and structural integrity of the tree.
AA: If using manual hand tools, which tools should be used for the various cuts?
Rogers: The type of tool used to make a pruning cut depends mainly on the size of the branch or limb being pruned. Hand pruners are rated for the maximum diameter of the branch they’re meant to cut — usually 1/2 to 1 inch. Look for top-quality construction, forged-steel alloy for bypass pruners. Make sure the tool is sized and balanced so that it feels comfortable in your hand. Don’t risk damage to the tree and tool by trying to force your way through larger branches. Instead, use a lopper.
Loppers provide extra reach and leverage for trimming growth as large as 3 inches in diameter. Like hand pruners, they’re available with bypass or anvil cutting action.
Look for steel alloy blades that are able to be re-sharpened on bypass-styles; replaceable blade and anvil on anvil styles. Handles should include comfortable, non-slip grips. If you buy just one set of loppers, a 26-inch bypass model is a good basic choice.
Pole pruners can come in very handy for high branches of less than 1 inch in diameter, especially in places where using a ladder would be dangerous. Some pole pruners can reach from 7 to 12 feet for a long overall reach. When choosing a pole pruner, you’ll want to look for a model that has a locking handle to reduce the chance of slippage when using the tool in an extended position. Pruners with a 360-degree rotating head can also come in handy when trying to cut high branches from an awkward position.
When branches are too big to cut cleanly with a hand pruner or a lopper (greater than 3 inches in diameter), it’s time to break out the hand saw. Saws are available in a wide variety of styles including straight and curved blades and with handles that are fixed or that fold for easy carrying. Look for blades designed with three-sided razor teeth. They offer more cutting efficiency than conventional saws. If you buy just one saw, make sure it’s large enough to handle medium to large branches. This will save time and help you do a better job.
AA: What should tree care professionals keep in mind when determining how much to prune/remove?
Rogers: First of all, don’t prune any tree unless it’s necessary. Every cut you make does put stress on the tree and opens it up for disease. When pruning off dead or diseased tissue, take off as much of it as you can without injuring the bark collar.
When dealing with live branches, it’s better to cut too little than too much. Although it’s not an ideal situation, you can remove more of a branch or limb later — but you can’t add it back once it’s been cut. The amount of live tissue to remove depends on the tree size, species and age as well as the reason why you’re pruning the tree in the first place. Younger trees will tolerate the removal of more living tissue than mature trees. Never remove more than one-third of the tree’s canopy in any growing season.