Safe and Sound: How Pruning Can Make Your Tree Strong
Understanding the Fundamentals of Structural Pruning
It’s only February, and maybe your trees aren’t on your mind. But this is a great time to discover whether your trees are safe and sound while they are in their leafless and languid resting phase. Let’s unpack that phrase: safe and sound. You want your trees to be safe for you and your property, and this is achieved when they are sound. That means they have good structure. Trees can have a good structure all by themselves, but often they would greatly benefit from some structural pruning.
Wait, what? Don’t trees know how to grow properly all by themselves? Yes, they do when they grow where they prefer to grow, which is among other trees in a forest. When they are planted in a lawn or they become one of the favored few remaining trees after development, they are literally out of their element. They can grow in ways that make them weaker than they would be in the forest.
Forest Trees
Let’s back up a bit and look at how trees grow in forests. Forest trees usually develop single trunks with well-spaced branches that have much smaller diameters than the trunk does. Their growth is directed mostly straight up because that’s where the sun is. Trees don’t waste energy growing long limbs into the shade of neighboring trees, so branches tend to remain short and strong.
The Sciency Stuff
Did you know that trees prune themselves in the forest? Cladoptosis is a fancy word for a tree’s ability to prune itself. When a limb is no longer useful to a tree, perhaps because it is now in too much shade, the tree will cut off nutrients and other essential products to that limb. It eventually falls from the tree and becomes part of the forest floor community by rotting and helping build healthy soil.
Next time you are on a forest walk, look at some tree trunks to see the scars where limbs were previously attached to the trunk. If it fell recently, you will see a distinctive “donut” shape around the wound that was created soon after the limb fell. This is a specialized tissue that helps the tree seal the wound and keeps the trunk safe from wood decay fungi. It is also how a wound seals when an arborist removes limbs properly.
Your Trees
Let’s contrast forest trees with what trees in the middle of lawns often look like. There are three things you should look for:
- First, you hope to see that your tree has a single straight trunk for most of its height and not two or more trunks. When trees get lots of sun from all sides, several trunks may grow and compete equally for size and dominance. We call these “co-dominant trunks” (sometimes called “co-dominant stems”). They crowd each other and are not as strongly attached as a trunk is to a true side limb. Trees with co-dominant trunks are prone to splitting.
- The second thing you might notice is that your tree has arching limbs that stretch very far from the trunk. They might be overly long because that part of the tree enjoys abundant sunshine and can continue to grow unrestricted by forest conditions. Limbs that have a diameter of 50% or more of the trunk’s diameter are prime candidates for reduction. These are the branches that are most likely to fail in wind and storms.
- The third thing to look for is crowded limbs along the trunk. When trees are small, it’s not a big problem. As limbs increase in girth, they may start to crowd each other and not have enough room to build strong trunk-to-branch attachments. These limbs are more prone to breaking out than well-spaced branches. If you’ve ever seen a Bradford pear with half its canopy lying over the driveway, you’ve seen this kind of failure.
Structural Pruning
Now that you’ve carefully examined your trees, perhaps you have seen some concerning things about their structures. The good news is that these things can be improved with some thoughtful and well-directed structural pruning. Trees that need a lot of help might need to be pruned every year. We don’t want to remove too much live growth at once for fear of harming the tree, so it is better to schedule pruning over several years.
Structural pruning starts with establishing one main, straight trunk. Co-dominant trunks can be removed or reduced. The second goal is to check growth on overly heavy or long limbs by shortening or sometimes even removing them. The third goal is to alleviate branch crowding. Some branches can be completely removed to relieve crowding, and others can be shortened and removed in the following years.
These are the essential steps of structural tree pruning. The goal is to replicate what this species typically looks like in a forest. But that does not mean we will do all these things to every tree!
Structural pruning can be performed on any tree, but younger trees that will become medium or large shade trees are the ones to prioritize first since they present more potential risk when mature. It’s important that these trees stay strong and safe.
You might think that your young sapling is too small to worry about. The first year is the ideal age to begin good structural pruning. Cuts are small, and young trees can accommodate a lot of pruning and bounce back with strong, properly directed growth. The beauty of this is that you can safely prune your own young trees with knowledge, quality hand pruners, and a small saw. If this excites your inner arborist, you can find guidance in our book, “From Wasteland to Wonder.” It’s free! You can look it up now!
How Big Can We Go?
There is a limit to how large a cut can be before the resulting wound is more damaging than the structural issue it is meant to address. If the diameter of the limb that was removed is more than 50% of the diameter of the trunk or limb that it was attached to, then it is inappropriately large. Good arborists will strive for cuts less than 30% wherever possible. Large cuts are damaging because decay organisms are almost certain to show up, and the tree then faces a race to seal the wound and contain the decay before it weakens the tree. This is an even bigger concern if a large cut is made at the trunk. Decay within the trunk could weaken the whole tree and possibly the roots.
What Structural Pruning Is Not
Structural pruning does not – and should not – account for aesthetics. Some trees look gawky and odd after they have been pruned for structure. It might be said that the tree is in its “awkward teenage years” after it has undergone some structural pruning. If the pruning is done well, the tree will respond appropriately and develop into a beauty. And if not quite a stunner, it will at least be stronger and safer.
Another recommendation, sometimes mistakenly called structural pruning, is to remove crossing and conflicting limbs. While this is not necessarily inappropriate, it’s more about aesthetics than strong structure. If this ends up being achieved because the pruning goal was really addressing crowded limbs, then that’s a bonus but should not be the goal.
And let’s not even talk about “topping”. Good grief! Cutting limbs in half all over your tree so that it looks “hat-racked” isn’t any kind of proper pruning at all. It doesn’t make your tree stronger or safer. As a matter of fact, it makes it weaker and, therefore, more hazardous.
Contact us if you want us to provide your trees with professional structural pruning. We really know how to help your tree become safe and strong!