The question of whether the Honey Locust (Gleditsia triacanthos) is invasive is complex and highly dependent on context. This deciduous tree, known for its adaptability, has a dual identity in landscapes across the globe. While the wild form possesses aggressive traits that allow it to colonize new environments rapidly, the varieties most often planted in urban settings are intentionally bred to be less problematic.
Defining the Honey Locust’s Native Range and Characteristics
The Honey Locust is native to central and eastern North America, ranging from Pennsylvania and Iowa south to Texas and Georgia. It thrives in the moist, organically rich soils of river valleys and floodplains, demonstrating a natural tolerance for drought and urban pollution. This inherent hardiness is why the tree has been widely cultivated and introduced worldwide.
The wild type of Gleditsia triacanthos is identified by two features: massive, branched thorns and long, dark seed pods. The thorns, which can reach up to 3 inches long, grow in clusters on the trunk and branches, posing a hazard in managed landscapes. The dark purplish-brown seed pods can grow up to 18 inches in length and contain a sweet, sticky pulp, which gives the tree its common name.
The sharp thorns and the messy litter of the large pods led horticulturists to develop thornless and often podless cultivars. Varieties such as ‘Sunburst’ or ‘Shademaster’ are predominantly sold in nurseries today. This intentional breeding largely excludes the wild, thorny species from most urban and residential plantings, as the wild species’ propensity for generating thorny thickets made it unsuitable for common landscaping.
The Nuance of Invasiveness
The Honey Locust is not officially listed as an invasive species across its entire native North American range, but its growth habits are aggressive enough to be considered a weed in certain contexts. In many parts of the Midwestern United States, the wild type is regarded as a pest that readily establishes itself in pastures and farm fields. Within its native habitat, it is better described as an aggressive native colonizer that thrives in disturbed or open areas.
The classification changes significantly when the tree is introduced outside of its native continent. In places like Australia, South Africa, and Argentina, the Honey Locust is unequivocally considered an invasive species. In these non-native environments, it lacks natural controls and forms dense, impenetrable thickets that out-compete native vegetation and dramatically alter local ecosystems. This distinction is important: an aggressive native plant is different from a non-native plant that disrupts an ecosystem, which is the definition of invasive.
The most common ornamental varieties, such as the thornless G. triacanthos var. inermis, are generally not considered invasive due to their reduced reproductive capacity. However, even seedless cultivars may still produce viable seeds. A thornless tree grown from seed may revert to the thorny, aggressive wild type, meaning a seemingly benign ornamental tree can still contribute to the spread of the wild species over time.
Mechanisms of Spread and Ecological Impact
The wild Honey Locust spreads effectively through two primary mechanisms: prolific seed dispersal and vegetative root growth. The tree begins producing seed pods around 10 years of age. The seeds themselves have a hard, impermeable outer coat, which requires a process called scarification to germinate.
This scarification process is often achieved through consumption by animals, a key element of the tree’s reproductive strategy. The sweet, sugary pulp of the long seed pods attracts herbivores, including cattle, deer, and rabbits, who consume the fruit. Passage through the digestive tract breaks down the hard seed coat, significantly increasing the germination rate. The seeds are then deposited in the animals’ dung, aiding dispersal over distances up to several kilometers.
The Honey Locust can also aggressively colonize an area through its root system by producing root suckers. These suckers are new shoots that emerge directly from the lateral roots of the parent tree, allowing for dense, clonal growth. This is especially common when the main trunk is damaged or removed. The tree’s tolerance for poor soil, drought, and high salinity gives it a competitive advantage, allowing it to quickly establish dense stands that crowd out less tolerant species.
Managing Unwanted Growth
Managing the aggressive growth of the Honey Locust requires a targeted approach, particularly when dealing with the wild type or root suckers from cultivated trees. The most common challenge is controlling the root suckers, which are often mistakenly pruned, leading to further sprouting. Root suckers should be removed by cutting them off cleanly at the point of emergence from the parent root or stem.
For established trees, simply cutting the trunk at ground level is counterproductive, as this often triggers a massive flush of aggressive root and stump sprouts. To effectively eliminate the tree and prevent regrowth, a systemic herbicide application to the stump’s cambium layer is necessary immediately following the cut. Herbicides containing triclopyr or picloram are often recommended for a cut-stump treatment, as they are absorbed by the root system to kill the entire plant.
For smaller, newly established wild seedlings, a foliar application of a systemic herbicide may be effective, provided the plant is less than six feet tall and has a healthy leaf canopy. Persistent monitoring and removal of new seedlings are necessary, as the seeds have a long viability and can continue to sprout for several years. Regular mowing can also help manage new suckers in turf areas.