A topped tree growing water sprouts. Photo: UME-HGIC
I love trees. I’m betting you do, too. They’re striking and statuesque. They shade us and inspire us, offer wildlife habitat, and provide a backbone to our landscapes.
But sometimes bad things happen to good trees. Well-intentioned but harmful practices such as topping threaten their health.
Pruning is good for trees. Done well, it can help to control size, remove potentially hazardous branches and improve both appearance and health. But bad pruning is harmful and can kill trees.
Topping – whacking off large limbs indiscriminately to stubs – is a very bad practice indeed. It’s damaging, dangerous, and expensive.
According to Dr. Alex Shigo, the world-renowned scientist and author of books on tree care, topping is the most serious injury you can inflict on a tree.
Why do people top trees? Most have trees too big for their space and feel topping is a good way to control size and prevent hazards. It’s not. Topping weakens trees.
In fact, a topped tree is much more prone to problems, including poor health and an inclination to drop branches or fall.
Leaves are food factories for trees. Since topping removes much of the leaf-bearing crown of a tree, it literally starves it.
Topped trees react by forcing out fistfuls of thin shoots around the cut to make more leaves. Creating these shoots drains even more energy.
A stressed tree is more vulnerable to insect and disease problems. The large, open wounds topping creates invite attack.
Good pruning cuts are made where a branch meets the trunk or another branch. Trees can heal this type of cut. Topping cuts in the middle of a branch create ugly stubs that often don’t heal.
Multiple large cuts – a staple of topping – create serious wounds. The exposed wood often decays and creates a pathway for infection. Columns of decay from repeat topping make a tree more likely to fall.
The multiple thin shoots that form near a topping cut are weak and bring problems all their own. They aren’t anchored in deep tissue like a normal branch, so they tend to break.
The thick regrowth of new branches also makes a tree top-heavy and more likely to catch the wind in a storm.
Also, topping is expensive. Topped trees need to be pruned regularly due to the rapid regrowth of all those skinny branches. Repeat toppings are more costly in the long run than proper professional pruning.
Topping has hidden costs, too. Weakened trees are more likely to cause damage by falling or dropping branches. And disfigured trees do nothing to enhance property values.
According to the International Society of Arboriculture, well-maintained, healthy trees can add 10 to 20 percent to the value of your property, while topped trees reduce value.
If a tree has overgrown its space, know that there are better options, including crown reduction or removal and replacement with a smaller tree. Just be safe and leave the big jobs for the pros.
Here’s our fact sheet on tree pruning that tells you more.
Topped trees are ugly, unhealthy, hazardous, and costly. Please don’t top your trees. I want you to enjoy happy, healthy trees for a very long time.
By Annette Cormany, Principal Agent Associate and Master Gardener Coordinator, Washington County, University of Maryland Extension.
Plastic tree tie embedded in a crapemyrtle trunk because it was not removed promptly. Photo: Miri Talabac, University of Maryland Extension
Q: There’s a crapemyrtle in our new yard that has a plastic cable tying it to a stake that has become stuck in the wood. Should I cut it out so the trunk can heal?
A: No, that will cause more damage and potentially lead to even more wood decay and crown dieback. All you can do is carefully cut off the excess outside the bark (don’t worry about making it flush; you don’t want to cut into live wood). Gardeners and landscapers should monitor any trees they stake for indications a trunk tie is abrading, cutting into, or being enveloped by the bark. Most trees don’t need staking, and even when they benefit from it, removal of the stakes and ties is recommended after six to twelve months of use. No tie or trunk brace should be so tight that the trunk cannot sway a bit in the wind.
It’s hard to predict how much of an impact the damage you found will have on the branches that particular trunk feeds. Fortunately, the tie in your case did not encircle the trunk, just brace one side of it; I’ve seen several instances where encircling ties become embedded and essentially strangle and kill the entire top of the tree (Leyland cypress and Arborvitae being common victims).
Tree and shrub wood expands outwards as it grows, increasing in diameter as each ring of new wood growth is formed yearly. Although an imperfect comparison, there are parallels to how coral reef colonies grow – over time, the innermost “skeleton” is no longer alive, though it provides support, and the outer shell of tissues is living and actively growing, save for the bark itself. (You can think of bark a bit like nails on a person or pet…it’s produced by live tissue, but the material itself is not alive.)
If the tie extensively obstructs the cambium that lies under the bark (the live tissues moving water, sugars, and nutrients around the tree), one or more major branches above it may die back in the coming years, for which there is no treatment. In some cases, the obstruction just becomes buried under years of growth, hiding it from view. (This is a hazardous situation if the tie or obstructing material were metal, and the tree was removed and chipped up one day.)
Trees can’t heal quite the way animals do, but with luck, this damage will remain minor and not cause significant dieback. If it does, though, you’ll have to cut down that trunk. Since crapemyrtle tends to sucker readily, new growth can take its place if you let a sucker mature into another trunk.
By Miri Talabac, Horticulturist, University of Maryland Extension Home & Garden Information Center. Miri writes the Garden Q&A for The Baltimore Sun and Washington Gardener Magazine. Read more by Miri.
Have a plant or insect question? The University of Maryland Extension has answers! Send your questions and photos to Ask Extension. Our horticulturists are available to answer your questions online, year-round.
Tree planting efforts are picking up as Maryland’s 5 Million Trees Initiative moves forward in 2024. Getting these trees – any landscape trees – off to a good start at planting time and through their first few years of establishment is important for their long-term growth and benefits to the environment.
At Ask Extension, we often receive photos of newly planted trees and older specimens with signs and symptoms of trouble. One of the things we do in our diagnostic process is look to see if there is a “root cause.” Is a girdling root present at the base of the tree trunk? Is the tree planted too deeply? Can we see a root flare? Today I want to bring these questions to the surface and explain why an exposed root flare can help prevent the formation of girding roots and why it matters for tree health and pest management.
A beech tree with normal, healthy root flare. Photo: Miri Talabac, University of Maryland Extension (UME)
What is a root flare?
The root flare is the area at the base of a tree trunk where the topmost roots emerge outward. This area is sometimes referred to as the trunk flare or root crown. In many species of trees, the trunk widens and curves outward (“flares”) like the base of a wine glass. This is illustrated nicely in this brief video by the University of Maryland Arboretum and Botanical Garden’s Outreach Coordinator, Meg Smolinkski.
What is the root flare of a tree?
When thinking about the trunk and root system of a tree, it is important to keep in mind: Roots need to be in the soil to get a steady supply of moisture and nutrients. The trunk (stem) portion should be out of the ground where exposure and good airflow help to keep the bark dry.
In our landscapes, we have many trees that are planted too deeply and the root flare is not visible at all. The trunks go straight into the ground like telephone poles. This can result in lower bark rotting, reduced oxygen supply to the roots, disease and pest problems, and girdling roots.
We have an epidemic of planting trees too deeply
At the University of Maryland Extension Advanced IPM Conference for the commercial horticulture industry last month, Jacob Hendee, an arborist for the Smithsonian Institution Gardens, talked about how common it is nowadays to see trees planted too deeply. Burying the root flare has reached “epidemic” proportions in our landscapes, he noted – and it is killing trees.
The main problem he addressed in his talk was that buried root flares can set the stage for stem girdling roots to develop unnoticed. Stem girdling roots (SGRs) grow around the tree’s base, rather than pointing outward away from the trunk as normal roots should. As girdling roots grow and enlarge, they compress the water- and nutrient-conducting tissues in the tree. This interrupts normal plant functions and can lead to symptoms such as leaf yellowing (chlorosis), smaller-than-normal leaves, leaf scorch (browning), branch tip dieback, and bark cracking. SGRs can and do result in overall tree decline and eventual failure.
An example of girdling roots. Photo: M. Talabac, UME
Looking at a cross-section of a tree trunk, the light-colored portion is the water-conducting sapwood (xylem). Source: Jacob Hendee, Smithsonian Gardens
When a stem girdling root forms around the trunk of a tree (represented in orange in the diagrams), it compresses and kills the water-conductive sapwood, which can result eventually in a dead tree.Source: Jacob Hendee, Smithsonian Gardens
Trees under moisture stress due to stem girdling roots become more susceptible to pests and diseases.Scale insects are significant pests of some landscape trees, as are some types of beetles and other insects. If a tree develops a pest issue, the pest may be secondary to the problem that made the tree vulnerable to the pest in the first place – stress.
Hendee emphasized that maintaining a visible root flare and preventing SGRs are practices of Integrated Pest Management (IPM). IPM involves using physical, cultural (plant care), and biological methods to manage pests and diseases, leaving chemical pesticides as a last resort. In the example of tree care, correct planting and monitoring to prevent stem girdling roots are key steps to preventing tree stress. Instead of thinking about killing secondary pests that show up on trees, think about how to prevent stressful growing conditions from the beginning and during the life of a tree. Trees with minimal stress are more resilient to insect pests and less likely to be overwhelmed by them or need intervention to recover.
How do stem girdling roots get started?
Hendee noted that plant care practices, both before planting (at the nursery), during planting, and afterward (over-mulching) contribute to this problem.
1. Many trees are grown too deeply in the nursery. Girdling roots can start to form inside nursery pots when the roots hit the container and start circling. This issue can worsen when young trees are moved into larger containers as they grow (such as saplings being transplanted into a bigger pot as they mature) and their roots are not loosened or pruned to correct deformities. Larger trees are sometimes planted too deeply in the nursery field and come to the customer in “ball and burlap” form with the root flare already covered in soil.
2. Many trees are planted too deeply at the time of installation. If the planting hole is dug too deeply, the root flare gets buried when the soil is filled back in, and often then further covered with mulch. In that situation, stem girdling roots can develop and worsen undetected.
3. Tree flares are often buried deeply in mulch. Too often we see huge piles of mulch – sometimes one foot high or more “mulch volcanoes” – around trees. This will keep the bark moist and can encourage new roots to sprout from the trunk above the main supporting roots (the flare). Those adventitious roots will grow upward for oxygen and may begin to girdle the flare and trunk. They will also be more vulnerable to moisture stress since the mulch does not retain water in the same way soil does. There is absolutely no horticultural basis for putting a big mound of mulch around a tree like this!
An example of incorrect mulching. Photo: Dr. David L. Clement, UME
Here fresh mulch was incorrectly placed on top of a girdling root and up against a tree trunk. Photo: C. Carignan, UME
What can you do? “Free the Flare”
1. Check the roots at planting time. If you purchase a container-grown tree, ensure it is free of circling roots inside of the pot. If you do find roots that are circling the root ball, cut through those roots with a pruner or other sharp tool. Set the roots in the planting hole so that they are pointing in an outward direction.
Prevent girdling roots when planting a container-grown tree
2. Keep the top of the root flare visible. Root flares should be above the soil line. Plant so the root flare is 2 to 4 inches above grade. When purchasing a container-grown or burlapped tree, you may need to wash away some of the soil to see where the root flare begins. If a landscaper is installing a tree for you, make sure they set the tree at the correct depth.
A hose was used to wash away the soil from a container-grown tree, revealing the top of the root flare. The difference in the lower bark color (on the trunk) indicates that the plant was several inches too deep in its container. Photo: M. Talabac
When a root flare is visibly present, it can help deflect any stem girdling roots that begin to grow, forcing them away from the trunk. It also makes it easier to see where girdling roots begin to form. Monitor the root flare area of your tree(s) regularly and cut through any circling roots that begin to grow. It is easier to cut wayward roots when they are small. The process of locating and remediating stem girdling roots on older trees can be very expensive.
Also note that some species of trees are more prone to developing girdling roots (e.g., maples), and sometimes girdling roots develop below the soil surface where they are not easily detectable except by above-ground clues. If you see symptoms of water stress in the canopy of an otherwise sufficiently-irrigated tree (e.g. leaf scorch, smaller-than-normal leaves), consult with a certified arborist for a tree assessment.
3. Don’t overdo it with the mulch! Keep a mulch-free buffer zone around the root flare. Hendee suggested leaving a 3 to 12-inch area bare around the base of the tree. Think of it as a donut hole: mulch should be laid down in the shape of a wide, shallow donut rather than a big heaping mound. The total depth of the mulch should be only about 2 to 4 inches.
Mulch applied correctly. 1 Free root flare, 2. Mulch-free buffer around the root flare, 3. 2 to 4 inches mulch depth, 4. Broad mulch width. Infographic by Smithsonian Gardens
For further exploration of these topics and correct tree-planting procedures, I recommend the following resources:
By Christa Carignan, Certified Professional Horticulturist & Coordinator, University of Maryland Extension Home and Garden Information Center. Read more posts by Christa.
Illustrations used with permission from Jacob Hendee, Smithsonian Gardens
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A collage of cherry (Prunus spp.) blossoms, some of which can be found in Washington DC. The species and varieties vary in blossom color, size, and shape. Credit: LiveJapan
Just across Maryland’s border, millions of people flock to Washington, DC at this time of year to witness the spectacular display of 3,000+ cherry trees in bloom around the Tidal Basin. Keeping these famous trees healthy from pests, predicting the timing of peak bloom, and mitigating the threat of rising tides from climate change are among the challenges that need to be addressed to keep these cherished plants in top form for people to enjoy now and for many years to come.
Dr. Lauren Schmitt, an ecologist working with the Burghardt lab in the University of Maryland’s Entomology Department, gives us a close look at the history of these magnificent trees, how pests are managed using an Integrated Pest Management (IPM) approach, how peak bloom times are predicted, and how some of the non-pest threats such as soil compaction and flooding are being addressed.
Read her two part-series on DC’s Famous Cherry Trees:
Lauren Schmitt, Ph.D. is an ecologist working at the intersection of ecosystem ecology and community ecology. A member of the University of Maryland Burghardt Lab, her research focuses on linking biodiversity and ecosystem function. Much of her work takes place in a forest diversity experiment, “BiodiversiTREE” to assess how tree diversity shapes communities and ecosystem processes.
