Killing crepe myrtle roots permanently almost always requires a systemic herbicide applied to a freshly cut stump, timed so the chemical rides the tree’s own internal plumbing down into the root system. Simply cutting a crepe myrtle to the ground rarely finishes the job, because the root network stays alive and sends up new shoots for months or even years. The good news is that with the right method and timing, a single treatment can deliver a kill rate well above 90 percent on woody stumps.
Why Crepe Myrtles Are So Hard to Kill
Crepe myrtles are deciduous trees and shrubs in the genus Lagerstroemia, prized for their summer blooms and peeling bark. They’re also survivors. When the trunk is damaged or cut, the root system responds by pushing out vigorous new shoots called suckers. This resprouting ability is an evolutionary advantage in fire-prone environments and a headache for anyone trying to remove one from a yard. A healthy crepe myrtle can send suckers up from roots several feet away from the original trunk, so even grinding the stump doesn’t guarantee the roots will stop trying.
The root system itself is broad and fibrous rather than deeply taprooted. Most roots sit in the top 12 to 18 inches of soil and extend well beyond the canopy drip line. That spread means mechanical removal by digging is labor-intensive and often incomplete. Leave a segment of living root behind and you’ll likely see new growth within a season. This is why chemical control, specifically a systemic herbicide that travels through the plant’s vascular tissue and kills roots from the inside out, is the standard recommendation.
The Cut Stump Method
The most reliable way to kill crepe myrtle roots is the cut stump technique. You cut the tree as close to ground level as practical, then immediately paint or spray a systemic herbicide onto the freshly exposed wood. “Immediately” matters here: the living cells on the stump surface begin to dry and seal within minutes. If you wait more than about 15 to 20 minutes, the cambium layer starts to close off, and the herbicide can’t enter the vascular system effectively. Treat the outer ring of the stump in particular, because that’s where the active transport tissue sits just beneath the bark.
Two herbicide active ingredients dominate this job. Glyphosate, the active ingredient in many broad-spectrum products, and triclopyr, a broadleaf-selective herbicide sold under various trade names, are both effective on cut stumps. Research on woody shrub control using the cut stump method found that both glyphosate and triclopyr were highly effective, though glyphosate provided slightly better results when lateral sprouting was factored in, and both worked well at concentrations lower than typically recommended on product labels.1Invasive Plant Science and Management. The Influence of Treatment Timing and Shrub Size on Chinese Privet (Ligustrum sinense) Control with Cut Stump Herbicide Treatments in the Southeastern United States While that study focused on Chinese privet rather than crepe myrtle specifically, the cut stump principle applies across woody species: you’re exploiting the same vascular pathway to deliver the herbicide to the roots.
For glyphosate, a concentrated solution of around 20 to 50 percent active ingredient is typically used for stump treatment, far stronger than the diluted spray you’d use on weeds. Triclopyr is often used at similar concentrations. Undiluted or minimally diluted products labeled for stump treatment are the simplest option. You don’t need to drench the stump. A thin, even coat across the entire cut surface, especially that outer ring of cambium, is enough. A cheap foam paintbrush works well and gives you more control than a spray bottle, which can send droplets onto nearby plants you want to keep.
Why Timing Makes a Difference
The cut stump method works year-round in a pinch, but timing it right improves your chances. The reason comes down to how trees move sugars internally. The phloem, the tissue just inside the bark, transports the products of photosynthesis, particularly sugars, from mature leaves down to areas of growth and storage, including the roots.2Fundamentals of Plant Physiology. Translocation in the Phloem When you apply herbicide to a fresh stump, you’re essentially hijacking that transport stream. The chemical gets pulled downward along with the sugars.
In late summer and early fall, deciduous trees are actively shuttling carbohydrates from their leaves into their roots to build energy reserves for winter. That downward flow is at its strongest, which means an herbicide applied to the stump during this window gets the best ride to the root tips. Spring treatment can also work. The same study on cut stump control of woody plants found that both spring and fall timings were effective.1Invasive Plant Science and Management. The Influence of Treatment Timing and Shrub Size on Chinese Privet (Ligustrum sinense) Control with Cut Stump Herbicide Treatments in the Southeastern United States The worst time is mid-winter when the tree is fully dormant and there’s minimal vascular activity, or early spring during the period of explosive upward sap flow, which can push the chemical away from the roots rather than toward them.
If you’re dealing with a crepe myrtle that has already been cut and is resprouting, you can still use this timing principle. Let the suckers grow enough to produce a decent canopy of leaves, then cut them back and treat the cut surfaces in late summer. The leaves will have been feeding the roots, and cutting during that active transport period ensures the herbicide follows the sugar stream downward.
Alternative Application Methods
The cut stump approach is the gold standard for crepe myrtles, but it’s not the only option. Several variations exist depending on the situation.
- Hack and squirt: For a standing tree you haven’t cut yet, you can make downward-angled cuts (hatchet cuts or drill holes) through the bark around the trunk’s circumference and squirt concentrated herbicide directly into the wounds. This works well when you want the tree to die in place before removal, or when felling isn’t practical. Space the cuts a few inches apart around the trunk so the herbicide reaches all sections of the vascular ring.
- Basal bark treatment: A triclopyr ester product mixed with a penetrating oil is painted or sprayed onto the lower 12 to 18 inches of bark on a standing tree. The oil carries the herbicide through the bark and into the cambium. This method works best on trees with trunk diameters under about 6 inches, because thicker bark on older trees makes penetration less reliable.
- Foliar spray: For small crepe myrtle suckers and regrowth under about 4 to 5 feet tall, you can spray the foliage with a systemic herbicide. The chemical enters through the leaves and translocates to the roots. This is practical for cleaning up scattered suckers after an initial stump treatment, but it’s rarely enough on its own to kill an established root system.
Each method has trade-offs. The hack-and-squirt approach is less disruptive to the surrounding landscape because the tree dies gradually without the immediate disturbance of felling and stump grinding. Basal bark treatment avoids cutting altogether, which can matter in tight spaces. But for a crepe myrtle you want gone permanently, cutting to a stump and treating that stump remains the most consistent performer.
Managing Suckers That Appear After Treatment
Even a well-executed stump treatment doesn’t always prevent every sucker. Crepe myrtles store energy in their root systems, and distant root segments may not receive a lethal dose of herbicide from a single application. If suckers appear weeks or months after treatment, don’t panic. This doesn’t necessarily mean the treatment failed entirely. It often means parts of the root system survived while the main root crown died.
The simplest fix is to let the suckers grow to about a foot or two in height and then either pull them or cut them and apply a small amount of herbicide to each cut. Repeated removal exhausts the root’s stored energy over time. Most people see sucker activity taper off after two or three rounds of removal within a single growing season.
Research on sucker control in other woody species has explored chemical growth regulators as an alternative to repeated cutting. A study on hazelnut sucker suppression found that 1-naphthaleneacetic acid (NAA) significantly reduced sucker height and fresh weight when applied as a sequential treatment, delaying regrowth by one to three times compared with untreated controls.3HortScience. 1-Naphthaleneacetic Acid (NAA) Reduces Sucker Growth in European Hazelnut (Corylus avellana L.) NAA is a synthetic plant hormone available in products marketed as sucker suppressants and tree wound paints. Applying it to a treated crepe myrtle stump after the initial herbicide application can slow sucker emergence and reduce the need for follow-up cutting. It won’t kill the roots on its own, but it buys time for the primary herbicide to finish its work.
Why Mechanical Removal Alone Usually Fails
Many people attempt to kill a crepe myrtle by cutting it down and grinding the stump, without any herbicide. Stump grinding removes the visible above-ground wood but only chews through the top few inches of root structure directly beneath the stump. The lateral roots, which extend several feet in every direction, remain alive and intact. Within weeks, suckers start popping up across the lawn, sometimes several feet from where the tree stood. Each sucker is essentially a new tree drawing on the old root system’s energy reserves.
Full mechanical root removal is theoretically possible but rarely practical. It means excavating the root zone to a depth of at least a foot across an area that may extend 10 to 15 feet or more from the trunk. In a typical yard with nearby structures, utilities, and other plantings, that level of excavation is expensive and destructive. And even then, any root fragments left behind can sprout.
Some homeowners try to starve roots by covering the stump and surrounding soil with a thick layer of plastic sheeting or landscape fabric. The idea is to block light from any emerging suckers, eventually depleting root energy. This can work, but it’s slow. Expect to keep the area covered for at least a full growing season and often two. It’s more effective as a supplement to chemical treatment than as a standalone method. If you’ve treated the stump with herbicide and then mulch or cover the area, the combination of chemical kill and light deprivation is more reliable than either approach alone.
Environmental Considerations Near Water
If your crepe myrtle sits near a pond, stream, or drainage area that holds standing water, the choice of herbicide and application method matters beyond just effectiveness. Triclopyr in particular has shown concerning off-target movement in wet conditions. Research tracking triclopyr behavior after basal bark application found that flooding events could release the herbicide into surface water and groundwater at concentrations high enough to cause significant defoliation of nearby non-target plants, with damage reaching as high as 92 percent in affected areas. In contrast, when activated charcoal barriers were present, triclopyr concentrations in monitoring wells stayed very low.4Weed Science. Physical and physiological pathways of off-target triclopyr movement and associated non-target injury following basal bark application
The practical takeaway: if your crepe myrtle is within a few yards of standing or flowing water, glyphosate applied directly to a cut stump is a safer bet than triclopyr. Several glyphosate formulations are labeled for use near aquatic areas. The cut stump method also minimizes the amount of chemical used compared with basal bark or foliar spray, which further reduces the chance of runoff reaching water. Avoid any herbicide application before heavy rain is forecast, since even a well-placed stump treatment can wash off before the tissue absorbs it fully.
Triclopyr can also cause non-target injury through soil activity independent of flooding, so gardens with shallow-rooted ornamentals near the treated stump may see collateral damage. If you’re using triclopyr in a densely planted area, the cut stump method with careful, brush-on application limits exposure far more than spraying does.
Glyphosate vs. Triclopyr for Crepe Myrtles
Both herbicides are systemic and both kill woody plants effectively, but they work differently and have different practical profiles. Glyphosate is non-selective, meaning it kills essentially any green plant tissue it contacts. Triclopyr is selective for broadleaf plants and won’t harm grasses, which can be an advantage if you’re treating a stump surrounded by lawn. However, that selectivity is only relevant for foliar spray or accidental drip. On a cut stump, both chemicals enter through the wood rather than through leaf tissue, so the selectivity distinction matters less.
Glyphosate tends to be cheaper and more widely available. Concentrated glyphosate products designed for stump and brush treatment are sold at most garden centers. Triclopyr products marketed for brush and stump use are also available but sometimes harder to find in concentrated form outside of professional supply channels.
For crepe myrtles specifically, glyphosate is the more common recommendation among extension services, partly because of its availability and partly because research on woody plant cut stump treatment found glyphosate had a slight edge in preventing lateral resprouting.1Invasive Plant Science and Management. The Influence of Treatment Timing and Shrub Size on Chinese Privet (Ligustrum sinense) Control with Cut Stump Herbicide Treatments in the Southeastern United States That said, the difference between the two is small in practice. If you already have triclopyr on hand and your crepe myrtle isn’t near water, it will do the job.
What to Plant After the Roots Die
Once the root system is dead, which you can confirm by the absence of new suckers for a full growing season, the old roots will decompose naturally over a period of one to several years depending on soil conditions. Warm, moist soil speeds decomposition. You don’t need to dig out every dead root before replanting, but larger root sections near the surface can interfere with new plantings and may attract termites or carpenter ants as they decay.
If you ground the stump initially, fill the resulting depression with a mix of topsoil and compost rather than the sawdust from grinding, which robs nitrogen from the surrounding soil as it breaks down. Give it a few months to settle before planting. If you didn’t grind and the stump remains, you can either let it rot in place (painting it with a nitrogen-rich fertilizer solution speeds this up) or hire someone to grind it once you’re confident the roots are dead.
Residual glyphosate in the soil is generally not a concern for new plantings. Glyphosate binds tightly to soil particles and is broken down by soil microorganisms, typically within weeks. Triclopyr persists somewhat longer, particularly in clay-heavy or waterlogged soils, but at the small quantities used in a single stump treatment, residues are unlikely to affect plants installed several months later. If you’re anxious about it, wait until the next growing season before putting anything new in the ground near the old stump site.