Learning Center


Reasons to Prune

Why do we prune? What is pruning? What are the types of pruning?

Some plants need to be pruned, thinned or trimmed back while others do just fine with no shaping, and can even look worse after pruning efforts.  In this post, we want to share more about the reasons to prune and in our next post, we are going to talk more about what to prune and when (link to that post will be in next weeks’ newsletter).  You can also check out our Gardening Calendar for some timing guidelines.

Quick aside on some terms; pruning usually indicates a slower process with selective cuts. This would be when you are cutting a branch or shoot, then stepping back to consider the next before cutting.  Pruning not only cuts off shoots, it encourages new growth in that the process typically allows more light to enter the interior of a plant. Shearing usually refers to cutting back the ends of most exterior branches to create a certain shape or maintain a certain height.  With ornamental grasses and groundcovers like liriope, shearing is cutting down the entire plant to a certain height. Thinning a plant is different still and is the preferred method for plants whose shoots come out of the ground, as opposed to off main trunks or larger branches.  Thinning can also refer to the removal of interior branches on a ‘regular’ shrub or tree.

Don’t prune just to prune. There needs to be a reason or why do it? You could be turning your low maintenance landscape into a high maintenance landscape for no good reason.  And if you prune, you need to know why you are pruning to know how to prune each particular plant.

Top Reasons to Prune

Shaping Plants

The first reason to prune is to create or maintain the shape of a plant.  Let’s say you have a plant you are trying to train into or keep in a certain shape.  An example of this might be a holly, shaped into a tight, pyramidal form.  Although some hollies naturally have this shape, you will need to shear it to keep the shape, especially if you are aiming for a formal, symmetrical look. Pruning to maintain shape may be as simple as pruning back a few leggy azalea shoots after the spring blooming season.

When pruning for shape, we often see shrubs that have been sheared to the same height year after year.  These plants typically only have a very thin layer of foliage on the outside of the plant.  We suggest keeping regularly sheared shrubs in a soft pyramidal shape as opposed to round; this way the foliage on the bottom of the plant would continue to get sunlight. When they are pruned into spheres, the top of the plant shades out sunlight to lower leaves and branches.

A Little More on Shaping Plants

Some plants do better than others when consistently sheared. For example, Compacta hollies tend to lose most, if not all, of the interior foliage after years of regular shearing. Other hollies, such as Nellie Stevens holly, seem to take consistent shearing better and keep more interior foliage.

Unless you are willing to invest some time (or money to have someone else do it) on regular pruning, it’s best to work with the natural shape of the plant and consider the mature size of a plant when planning your landscape. Trying to keep a large plant at much smaller size can also stress a plant, making it more susceptible to disease and insect issues.

While there are specific times of year to do a ‘hard’ prune, most plants will be fine with a light shaping any time year.  You can go ahead and cut that wild abelia shoot off in the summer, no problem!

Create and Maintain Special Feature

All topiaries from geometric to fanciful, will require trimming or pruning. And so will espaliered trees or shrubs.  You may also choose to grow that huge loropetalum as a tree instead of a large shrubs, which will require removing lower branches. Before you cut, keep in mind that maintaining a shape that is far from a plants’ natural shape will be more work.  But many people find it therapeutic so we aren’t trying to talk you out of it!

Healthier Plants

Pruning is also often done to assist a plant in recovery from storm damage, such as the removal of branches broken under the weight of snow or ice. Portions of plants may also expire due to root injury, wind or mechanical damage. A good time to assess the situation is late winter or early spring. If branches break easily and show no green when the outer bark is scraped back, it may be a dead branch. Cut back to a living portion of the branch or further if needed to maintain a good shape. If you see dead branches during the growing season, it’s fine to prune those out then as well. If it’s winter, and you aren’t sure, feel free to wait until spring to see if the branch that might be dead leafs out and prune when it becomes obvious it won’t. Promptly address dead branches that may be hazard to people, pets or property.

You might also need to occasionally prune tree branches that have a narrow angle to the trunk as opposed to a more typical, stronger wide angle.  Picture a tree trunk and a branch growing from it.  The closer it is to a 90 degree angle, the stronger it is. The more narrow that angle is, the more susceptible to breakage it can be.  One well known example of this issue is the Bradford pear, a tree notorious for for splitting.  The natural structure of Bradfords includes narrow branches so we suggest choosing an alternate tree.  Most trees have wider branch angles and only the occasional narrow angled branch that will need to be removed.

Control Disease or Insects

Severe disease and insect infestations can be another reason to prune.  An example of this would be a crapemyrtle taken over by crapemyrtle bark scale (learn more about crapemyrtle bark scale in this post).  If you have tried all the other control methods and can’t get it under control, reducing the size of the plant can help in controlling a persistent pest.  We would caution against this being the initial go-to method of resolution though.

Thinning a shrub can increase air flow; good air flow will reduce disease and insect issues.  Thinning a plant will also make controlling these pest issues easier.

Rejuvenate Aging Plants

As mentioned above, pruning can encourage new growth, which creates another good reason to prune… to rejuvenate aging plants.  Plants don’t live forever but by taking good care of them, you can extend their lifetime.  Let’s say you just moved into a home and you are seeing plants with dead branches, or maybe the boxwoods only have foliage on the outside.

These plants might benefit from being cut back severely.  That may sound er, severe, but what we mean by that is they need to be cut back further than usually recommended to remove dead or dying branches. If the roots are healthy, new shoots should emerge and a new shape can be developed.  If the roots aren’t healthy, the plant may not recover from a hard pruning.  You might not know until you try to rehabilitate a plant.  Sometimes, these drastic measures are worth it to try to recover a plant. Sometimes not; that choice is yours to make.

Increase Blooms or Fruit

Careful pruning of fruits (both trees and brambles) will encourage blooming and therefore, fruiting. Deadheading (removal of spent blooms) shrubs or perennials that rebloom throughout the season will encourage new blooms. Shrubs like roses and butterfly bushes bloom best on younger, vigorous growth and later in the season. Since pruning encourages this growth, the action increases blooming.

Bottom Line

In conclusion; you don’t need to prune just to prune. Have a reason in mind. If you don’t start with a good reason, determining what your next cut will be is difficult.

Try to work with the plants’ natural shape; most plants have a wonderful natural shape. And, in general, avoid removing more than 30% of the top growth at any time. Exceptions are cleaning up or cutting back perennials and groundcover such as liriope.

Now that we have introduced you to the reasons to prune, we suggest reading our next pruning post; When and What to Prune in Arkansas.  This is key because some plants bloom only on current years’ growth (also called new wood), while others bloom on last years’ growth (old wood). This means that if you trim certain plants at the wrong time of year, you may be drastically reducing your blooms…eek!