Pruning

Proper Tree Pruning: Art & Science

It's time for another tree care lesson! If you need a refresher on why we value trees so much, check out our post on the top 10 benefits of urban trees. Today we'll talk about proper pruning technique and why it's so important. The tree you see above has completely closed off some cuts and is working on others with even, donut-shaped callus growing over the wound. That's what you want to see, but getting that result is harder than you might think.

If you've ever needed to prune a tree branch and you haven't been trained on the best methods, chances are you've done one of two things: cut the branch somewhere in the middle to meet whatever clearance needs you're trying to achieve, or cut the branch off flush with the trunk. Both of these are bad for the tree. Trees can't heal wounds in the way people heal cuts on their skin. The tree has to grow new bark from the areas around the cut to seal off the damage, and some parts of the tree are better at this than others. When you cut a branch in the middle, the bark just below that wound can't wrap around and seal off the cut, so instead the branch just dies back to a spot lower down the branch where it can seal itself off, and you're left with a stub that will die. If you cut the branch flush with the trunk, you're creating a much larger wound that provides a bigger area for insects and disease to invade, and it takes longer for the tree to seal it off. The tree pictured above has been pruned properly, and you can see that new bark has totally covered the cuts over the years. Learn how to get these results below.

So where should you make a cut? There's a sweet spot at the base of a branch just before where it connects to another limb or to the trunk. There is a ridge of bark on the top of the branch and a little bump called the branch collar on the bottom. Your goal is to cut just on the outside of these two structure. See the diagram on the right for clarification (click to see larger). It won't always be easy to spot the branch collar on the bottom, so if you aren't sure make your best guess. The angle of the cut should follow the angle of an imaginary line connecting the bark ridge and branch collar. If you're having trouble finding the branch collar, make the angle match the angle of the bark ridge as it extends into the trunk.

Step 1: cut a notch (red arrow) on the underside of the branch about a third of the way through

Step 1: cut a notch (red arrow) on the underside of the branch about a third of the way through

Step 2: cut the branch all the way through at least 4-6” past the notch (red arrow) you cut in step 1

Step 2: cut the branch all the way through at least 4-6” past the notch (red arrow) you cut in step 1

Step 3: make your final cut just outside the bark ridge (red arrow) at an angle away from the tree

Step 3: make your final cut just outside the bark ridge (red arrow) at an angle away from the tree

If you look at a branch that has broken off in a storm, you will sometimes notice that the weight of the falling branch caused a strip of bark to rip off of the trunk as it fell. This can also happen when a branch breaks as you work on sawing through it, and ripping bark like that leaves a wound that can be difficult for a tree to heal over. If you are removing a branch larger than 1" in diameter, you need to use the three cut technique to avoid tearing the bark. First you make a cut on the bottom of the branch further up than where your ideal cutting zone is. This cut should go about a third of the way into the branch. Next, you cut off the branch on the outside of this pre-cut. If the bark starts to rip, it will stop when it gets to your first cut. Your third cut should be at the base of the branch in the sweet spot we discussed above.

Congratulations! You now know how to prune your trees to keep them happy and healthy for years to come! Please spread your knowledge, and never hesitate to ask a professional for help if you have questions. If you’re more of a visual learner, here’s short video that shows how to cut medium-sized branches and shows where you want the finishing cut for any size of branch. For more details written instructions, you can also check out this Purdue Extension bulletin about pruning trees and shrubs.


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To Shear or Not to Shear? How to Prune Shrubs

It's the time of the year where you're probably starting to think about tidying up wayward shrubs and pruning hedges during the spring growth spurt. But before you grab shears or gas-powered hedge trimmers, let's talk about proper pruning practices and how they differ from species to species. Not all shrubs can be pruned the same if you want them to live long and prosper.

Rule #1 is to put away your electric or gas-powered hedge trimmers. Unless you're maintaining a substantial yew hedge or something like that, this tool doesn't have a place in shrub pruning. They can be useful for cutting back ornamental grasses or other sturdy perennials, but when used on shrubs they can tear and tatter twigs ends and leave the shrub vulnerable to pest and disease problems, along with leaving unsightly dead tips on branches.

Yews are one of a handful of shrubs that does well with tight shearing, as seen in this image of our work. Photo by Maria Gulley

Yews are one of a handful of shrubs that does well with tight shearing, as seen in this image of our work.
Photo by Maria Gulley

Even if you're using sharp, clean hand shears, a tight globe or box look is not suitable for every shrub in the landscape. For some species, this kind of pruning can result in poor internal structure that leaves huge holes in the shrub if even a single branch is lost. Pruning shrubs into uniform shapes can also rob them of the beauty of their natural form. We pick shrubs not just to provide a desired flower color or fill a space; when we design we take into account the natural shape and texture of a shrub, and if you shear a shrub that isn’t meant to be sheared, you’ll lose its natural beauty. You can also be giving yourself a headache, as some species will fight back with aggressive shoot growth after shearing. If you've ever tried to shear forsythia, you know what I'm talking about.

However, there are times when you want or need the clean formal shapes that a pair of hedge clippers can bring. The following species tolerate shearing well: arborvitae, yew, boxwood, privet*, barberry*, and burning bush*. When shearing a hedge, keep the top slightly narrower than the base. Hedges that are narrower at the bottom often end up thin and scraggly at the bottom because sunlight can't reach the lower branches.

Diagram of proper shrub pruning to reduce overall size. Click to view larger.

So how do you keep other species of shrubs in check if shearing isn't an option? Selective pruning is the process of removing individual branches to control the size and shape of your shrub or promote without destroying its natural shape. Branches can be cut back where they connect to a larger branch or snipped off just above a lower bud. If it seems like the bush is getting too dense and crowded, limbs can be removed all the way down to the ground. Make sure you look twice and cut once so you don't accidentally remove a limb that will leave a bare spot. This may be unavoidable at first if you're switching from shearing to selective pruning, but with time it will be easier. See the diagram on the left for an illustration of selective pruning.

If this seems like a lot of work, don't worry. Once you ditch the shears and pick up the hand pruners, you'll notice that your shrubs need considerably less taming. You will rarely see long, leggy shoots springing up left and right once you switch your methods and stick to it. Instead you'll just be removing the occasional wayward shoot and periodically reducing the shrub's size. If your shrubs have been sheared for so long that you are left with dense growth on the outer few inches and twiggy, leafless growth on the inside, then you may need to resort to renewal or rejuvenation pruning to bring it back to a healthy habit.

Forsythia especially dislikes shearing.  By Rdsmith4 - Own work, CC BY-SA 2.5

Forsythia especially dislikes shearing.
By Rdsmith4 - Own work, CC BY-SA 2.5

One last consideration in pruning is timing. Pruning should be done when the plant has the most time to recover, such as early spring or early summer (unless you're cutting just a few stems - you can do that any time without doing the plant any real harm). If you prune in the hottest part of the summer when your shrub is already stressed, you can increase the plant's stress and make it more vulnerable to other problems. Pruning in the fall can encourage new growth that won't have enough time to mature before freezing temperatures arrive, especially if you're shearing a hedge. Flowering shrubs need to be pruned at different times of year depending on when they flower. Spring blooming shrubs usually develop next year's flower buds during the summer, so it's vital that you prune immediately after flowering so you don't remove next year's flower buds. Summer blooming shrubs usually bloom on new growth, so they should be pruned after flowering, but before new growth starts in spring. Some shrubs can be pruned at any time, because they bloom on both new and old stems. Below I've listed some common flowering shrubs by optimum pruning time.

Prune in spring immediately after flowering:

  • Deutzia (Deutzia gracilis)

  • Forsythia (Forsythia x intermedia)

  • Rhododendron and Azalea (Rhododendron species)

  • Thunberg Spirea (Spiraea thunbergii) (varieties include 'Ogon')

  • Lilac (Syringa species)

  • Viburnum (Viburnum species)

  • Weigela (Weigela hybrids)

  • Dwarf Fothergilla (Fothergilla x gardenii)

  • Chokeberry (Aronia arbutifolia and melanocarpa)

  • Red Twig Dogwood (Cornus sericea)

  • Oak Leaf Hydrangea (Hydrangea quercifolia)

  • Big Leaf Hydrangea (Hydrangea macrophylla)

Prune before spring growth:

  • Butterfly Bush (Buddleia hybrids and species)

  • Beautyberry (Callicarpa species and hybrids)

  • Smooth Hydrangea (Hydrangea arborescens, varieties include 'Annabelle', 'Incrediball', 'Invincibelle Spirit')

  • Hardy Hydrangea (Hydrangea paniculata, varieties include 'Limelight', 'Pinky Winky', 'Quick Fire')

  • Sumac (Rhus species)

  • Virginia Sweetspire (Itea virginica)

  • Summersweet Clethra (Clethra alnifolia)

  • Bumald Spirea (Spiraea x bumalda, varieties include 'Anthony Waterer')

  • Winterberry (Ilex verticillata)


Prune before or after blooming:

  • Reblooming Hydrangeas (Hydrangea macrophylla, specific varieties such as Endless Summer series)

  • Knock-Out Roses (Rosa Knock-Out hybrids)

  • Japanese Spirea (Spiraea japonica, varieties include 'Little Princess', 'Goldflame', 'Magic Carpet')

Azalea Photo by Maria Gulley

Azalea
Photo by Maria Gulley

Dwarf Fothergilla Photo by Maria Gulley

Dwarf Fothergilla
Photo by Maria Gulley

Smooth Hydrangea Photo by Maria Gulley

Smooth Hydrangea
Photo by Maria Gulley

Knock-Out Rose Photo by Maria Gulley

Knock-Out Rose
Photo by Maria Gulley

I've provided some additional resources on pruning shrubs below. Feel free to direct any other questions you may have to me. Good pruning practices are essential to the long-term health and beauty of your garden, and we’d like to help. Contact us to learn more about what our maintenance team can do for you.

Additional Resources:
Pruning Ornamental Trees and Shrubs (Purdue University Extension)
Shrub Pruning Calendar (Virginia Cooperative Extension)

*Privet, barberry, and burning bush are considered invasive and should be avoided. Privet and barberry are included in Indiana’s newly adopted list of banned invasive plants, and they will not be available for purchase within a few years.


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Proper Tree Pruning: an Art & a Science

Proper Tree Pruning: an Art & a Science

It's time for another tree care lesson! If you need a refresher on why we value trees so much, check out our post on the top 10 benefits of urban trees. Today we'll talk about proper pruning technique and why it's so important. The tree you see below has completely closed off some cuts and is working on others with even, donut-shaped callus growing over the wound. That's what you want to see, but getting that result is harder than you think.

A Topped Tree Is the Devil's Playground

Is this an overly dramatic post title? Possibly, but I also had fun with it, so we're sticking with it. But good tree care is a serious deal. When properly cared for, a tree can boost property value, provide shade, shelter wildlife, and improve human well-being. Bad management practices, such as topping, can turn an otherwise wonderful tree into a potential safety hazard for many years in the future and kill it in the long run.