Locust trees, encompassing species like the Black Locust (Robinia pseudoacacia) and Honey Locust (Gleditsia triacanthos), are recognized for their rapid growth and adaptability. While they offer benefits in certain landscapes, their vigorous root growth can present specific challenges.
Characteristics of Locust Root Systems
Locust trees generally possess extensive and robust root systems. Black Locust trees are particularly known for their fibrous and wide-spreading roots, which can range from shallow to deep depending on soil conditions. These roots are highly adventitious, readily producing new shoots, especially when disturbed or cut. This leads to prolific suckering, where new stems emerge from the root system, often forming dense thickets.
In contrast, Honey Locust trees typically develop a strong taproot that can extend deep into the soil, sometimes reaching 10 to 20 feet. While they also have a profusely branched root system, they are less prone to widespread suckering than Black Locust, though root sprouts can still occur, particularly if the tree is stressed or cut. Both species are legumes, fixing nitrogen in the soil through root nodules, which contributes to their vigorous growth and ability to thrive in various soil types.
Common Challenges from Locust Roots
Locust root systems can lead to several common problems in residential and garden settings. Black Locust frequently sends up numerous root sprouts across lawns, garden beds, and even paved areas. These suckers can quickly establish, creating thorny thickets that are difficult to manage and can outcompete desired plants for water and nutrients. Their pervasive spread often extends beyond the tree’s canopy, invading neighboring properties.
Less commonly, the strong and widespread roots of both Black and Honey Locust can pose a risk to hardscapes. Vigorous root growth near foundations, sidewalks, or driveways may lead to cracking or lifting over time. The constant emergence of new shoots requires frequent removal to maintain a tidy landscape.
Strategies for Managing Locust Roots
Managing locust roots, particularly the suckering tendency, requires consistent effort. For Black Locust, regular mowing of areas where suckers appear can help suppress their growth, as repeated cutting depletes the root’s energy reserves. Severing suckers at their point of origin on the main root, rather than just cutting them at ground level, can be more effective. Applying a broadleaf weed killer to individual suckers in the fall, when the tree is translocating nutrients to its roots, can provide better control.
Installing a physical root barrier during planting can prevent root spread and suckering for new trees, directing roots downward and containing lateral expansion. When planting any locust tree, selecting a location away from structures, utility lines, and other garden plantings can minimize future conflicts. For Honey Locust, which suckers less, simply mowing over any emerging sprouts often suffices to keep them in check.
Complete Removal of Locust Trees and Roots
Complete removal of a locust tree and its root system is a substantial undertaking due to their persistent nature. Cutting down the tree alone often stimulates aggressive suckering from the extensive root network. To effectively eliminate the tree, it is important to treat the stump immediately after felling. Applying a systemic herbicide to the fresh cut surface, specifically the cambium layer, allows the chemical to be transported throughout the root system, inhibiting regrowth. Herbicides containing active ingredients like picloram, aminopyralid, triclopyr, or glyphosate are often recommended.
Stump grinding can remove the visible stump, but it may not eliminate all the subterranean roots, which can still produce suckers. Continued vigilance is necessary, as remaining root fragments can sprout for several years. Any new suckers should be promptly treated with herbicide or repeatedly cut to exhaust the remaining root energy, eventually leading to their decline.