Damon Edward Abdi

At the LSU AgCenter, issues echoed at extension events guide research programming to meet the needs of the community. From parish agents to professional horticulturists to the general public, supporting tree establishment in the landscape is a commonly cited concern. After all, poor installation methods can lead to long-term loss of our invaluable urban canopy and the cooling effect it provides for our communities.

Planting sites throughout Louisiana pose a plethora of challenges. Compacted soils in urban environments and new construction sites can limit root growth while remote roadside plantings relegated to limited attention may languish if left unmonitored. The range of unique, site-specific challenges are only exceeded by the spectrum of solutions suggested to support tree establishment.

Proper installation practices are imperative to the long-term success of a tree. While certain aspects of tree planting are widely recognized as best practices, such as digging a planting hole at least twice the width and slightly shallower than the root ball, root modifications made prior to planting are subject to far more debate.

The root system of container-grown plants is confined to a limited volume and can cause circling roots if left for too long. This garners the attention of concerned gardeners, and opinions abound as to the best way to rectify this issue before installation. While some may dismiss concerns about this potential problem, simply placing the plant into the hole without worry, many people profess that some form of preplanting root modification is necessary to support successful establishment. Modification practices include simple solutions such as scoring the root ball with a knife or severing the base of the root ball with a spade, whereas more intensive methods may include manually manipulating the roots. Conversations with stakeholders and hobby horticulturists at extension events yield no consensus on which practice is preferred; however, this inspired programming to turn anecdotal evidence into applied research to benefit our community.

At the Hammond Research Station, a variety of projects and methods surrounding sustainable tree installation practices are shedding light on ways to protect the urban canopy. The first project began with selecting a popular landscape tree, the Natchez crape myrtle (Lagerstroemia indica), as the model plant. Plants were grown for two seasons in a too-small-for-comfort container to develop circling roots before planting. The installation site was uniformly prepared by excavating holes exactly twice the width and slightly less than the depth of the root ball, arranged in parallel rows in the Cahawba fine sandy loam soils on-site. In April 2023, crape myrtles were installed with no root modification as the control while three manipulation practices of increasing intensity were also investigated:

• A “four-cut” method of vertically scoring the root ball, a practice most homeowners and hobbyists use
• A “chop” method where the bottom 2 inches of the root ball are sliced off with a shovel, a practice relayed by local stakeholders
• A “butterfly” practice where roots are hand-splayed, a practice performed by the most meticulous of gardeners

Adhering to best management practices, the native soil was used as a backfill. All fertilizer, pesticide and irrigation practices were uniformly administered for all treatments as the crape myrtles endured what felt like a never-ending drought that summer and several spells of bitter cold during winter months. Over the ensuing year and a half, growth index (the average of the height and perpendicular widths of the plant) and stem caliper (diameter of the largest single trunk in this often multistemmed species) were measured. Growth index was uniform across all treatments, indicating no differences in the size of the plant. Stem caliper was also the same between treatments, save for one sample date in the middle of the study.

While the sizes were visually and quantitatively the same, digging deeper was literally necessary to identify the effects of the preplant root modifications. Plants were excavated in October of 2024, preserving the exact same volume of soil for each replicate by using a hydraulic tree spade. Root masses were carefully cleaned, first with water and followed with an air compressor, before visual inspection and biomass assessments. While it was observed that unmanipulated roots exhibited continued circling, manifesting in a vortexlike appearance of the root mass, this was far less prominent in any of the preplanting modified root systems. While qualitatively noticeable, there were no quantitative differences in the dry weight of the root systems or the dry weight of the aboveground biomass (trunk and stems of the trees).

So, does this mean we should do nothing to the roots before planting? One study investigating one species over one and a half years on one site — with a relatively forgiving soil type — is certainly not enough to make grandiose claims; however, it serves to start a larger conversation. That dialogue continues with active research investigating preplant root modifications of swamp maples (Acer rubrum L. var. drummondii) grown in either larger, 30-gallon containers or balled-and-burlapped production methods. It will also include new preplanting treatments, such as shaving root systems with a reciprocating saw for container plants and removing the wire basket from balled-and-burlapped plants.

Projects investigating Abelia establishment through a partnered program with local high school students expand the scope of this work to new species — and to the next generation of Louisiana horticulturists.

Finally, integrating the insights of our industry members toward real-world scenarios provides new practices to implement. One such method is elevated planting in particularly compacted soils, where plants are installed almost completely above grade and soil is built up around it. Through harvesting insights from the community and developing research to put practices to the test, the LSU AgCenter harmonizes extension and research to solve the pressing problems people face.

Damon Edward Abdi is an assistant professor of landscape horticulture at the LSU AgCenter Hammond Research Station.

This article appears in the summer 2025 edition of Louisiana Agriculture.

After excavation, root balls were cleaned first by hose and second by using an air compressor to remove remaining soil particles. Roots of trees that were not manipulated exhibited a vortexlike circling at times. Photos by Damon Abdi

Using a hydraulic tree spade, plants were removed after one and a half years in the landscape. The hydraulic tree spade allowed consistent excavation practices for each tree and treatment. Photos by Damon Abdi

Using a hydraulic tree spade, plants were removed after one and a half years in the landscape. The hydraulic tree spade allowed consistent excavation practices for each tree and treatment. Photos by Damon Abdi

Manipulating the roots of larger nursery plants may require more advanced tools, such as a reciprocating saw, in order to quickly and efficiently shave the outer root ball. Photo by Jonathan Ford

Using a knife to score the edge of the root ball is one of the more common preplanting methods to address circling roots for smaller plants. Photo by Damon Abdi