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Arboriculture / Tree Care

Pruning

Before we give you the keys to the car by telling you what to prune, a little education is in order on how to make a proper pruning cut. As every pruning cut is a wound to the tree, care must be taken to minimize damage caused by pruning cuts and to minimize their number and size. The proper pruning cuts, made in the right places and at the right time of year can keep your tree beautiful and safe.

How to Prune

Natural target pruning is the fancy name for making the proper pruning cut. Natural target pruning (NTP) will allow the tree to heal the pruning wound as quickly as possible. NTP wounds heal faster because the cut is made as small as possible (as opposed to flush cutting) with the minimum amount of dead wood remaining (as opposed to leaving a stub). They also are less noticible than the stub cut or flush cut.

Pruning diagrams

The key to NTP is finding the branch collar which is the natural target for the cut. The pruning cut should always be just outside of this collar, but not far enough to leave a stub of branch. The branch collar is evident on many species of tree, some more than others. It is the base of the branch where the natural branch taper begins to flare out as it connects to the limb or trunk. Again, the branch collar should never be injured, cut into or compromized in any way. Some trees make it a little harder on us to find the target cut, but for them there is another rule of thumb generalization developed by Dr. Alex Shigo. Find the branch bark ridge, it is the area of raised bark extending down from the crotch. Find the line perpendicular to the branch to be pruned. Make your cut half way between the two. Using these rules of thumb guideline, the average person can make a pretty good pruning cut.

If the branch to be pruned is larger than you can control easily it necessary to make a 3-part cut to ensure that the bark does not tear down the limb or trunk, resulting in an embarrassing scar and a larger wound. The 3-part cut is done by making an undercut about a foot from the branch collar. End this cut just as the branch is beginning to grab the saw. Directly above the undercut or slightly further our the limb, make the second cut, holding onto the branch so that it can be controlled as it falls. Finish with an NTP cut at the branch collar.

Types of Pruning

The type of pruning that an arborist does is based on the goals of the tree owner. Do you want a little more light in the back yard under that Norway maple? You are probably asking for canopy thinning or canopy raising. Want to give those rhododendrons a little more space under the pines? Canopy raising is accomplished by taking low hanging branches. This is also what is done when roof clearance is needed.

If you are looking into a tree and say, “What a mess!” you’re looking for a structural prune. By this the arborist means pruning to make the canopy of the tree more structurally balanced, stable and less likely to cause problems for the health of the tree in the future. Broken, crossing and rubbing branches are removed, along with co-dominant leaders, branches with narrow angles of attachment. Typically, large pieces of deadwood, both attached and hanging, are removed from the tree in this procedure as well.

If you have a pin oak and have noticed all of the little dead branches in the interior, you are looking for removal of deadwood. There is generally a size range given for deadwood removal, for example “Remove deadwood 2 in. +” means that deadwood greater than wrist size will be removed from the tree. If you are able, fine pruning of the majority of the deadwood in a tree (1/4 in. +) can provide multiple benefits. Not only can it tremendously improve the appearance of many species of trees, it can also give a baseline in a tree suspected of having of having health problems for monitoring the rate of dieback.

Establishment pruning is an easy and cost effective way for an owner of a young tree to minimize the future cost of maintenance for that tree. Proper scaffold branch spacing, removal of co-dominant leaders, and removal of crossing branches are all things that can be taken care of for pennies on the dollar when a tree is small. In addition, smaller pruning cuts mean smaller wounds that a vigorous young tree can quickly heal over and recover from.

Canopy reduction pruning has the least effect on the health of the tree when it is relatively young (not past “middle age”), when the pruning cuts can be small and the tree can heal them efficiently. In a mature tree, even “drop crotch” pruning (the industry standard method for reducing the height of a tree) can leave large wounds that the tree may never heal over. Canopy reduction pruning should be practiced on trees that are just getting to the height at which the tree owner would like the tree to be maintained and when the cuts can be kept small.

What to Prune

Pruning is an art form as much as a science. There are some basics that can guide one on their way. Most of the pruning that the homeowner will be doing will be establishment pruning or maintenance of small ornamental trees. In these cases it’s relatively simple. Remove dead, damaged or diseased branches; remove crossing or rubbing branches; remove inward growing branches; and thin out branches that are right on top of each other or redundant branches.

Different shapes or effects can be achieved on small ornamental trees such as Japanese maples and flowering dogwoods through more thoughtful pruning. Take your time with the tree. See how it wants to grow in its space, how the sunlight is effecting it, how it interacts with the rest of the landscape. This is the art of pruning and it requires patience, knowledge of your medium, and observation. If you still feel overwhelmed, or uncertain, call a professional arborist and watch.