Crown vetch (Securigera varia, formerly Coronilla varia) is a perennial legume with a trailing, sprawling growth habit. This herbaceous vine typically forms thick mats of foliage with stems up to six feet long. It is marked by compound, fern-like leaves containing 15 to 25 small leaflets, and characteristic pea-like flowers.
The flowers bloom from late spring through summer, clustered in dense, spherical groups resembling small crowns, often ranging from white to pink or purple. Crown vetch is not native to North America, originating in Europe, Asia, and northern Africa. It was introduced to the United States in the mid-1800s, with widespread use beginning in the 1950s for land management.
Primary Applications in Land Management
Crown vetch was initially embraced throughout North America for large-scale soil stabilization projects. It was promoted as a solution for erosion control, particularly in areas difficult to maintain or revegetate. Its dense, mat-forming growth habit and fibrous root system provided reliable cover for exposed earth.
One of the most extensive uses was along transportation corridors, where it was planted to stabilize steep highway and roadside embankments. Beyond roadways, crown vetch was also used extensively in land reclamation efforts, such as revegetating abandoned mine sites and railroad embankments.
Federal guidelines established in 1977 often required the establishment of 70% perennial ground cover on abandoned mine sites, and crown vetch provided the rapid, dense coverage needed to meet this standard. The plant has also been utilized as a bank stabilizer along waterways and as a temporary ground cover in various other large-scale construction or waste areas. Its use continues in some regions for attracting pollinators or as a forage crop, although these applications are now overshadowed by its drawbacks.
Appealing Traits and Advantages
A primary benefit of crown vetch is its capacity to thrive in difficult environments with minimal human intervention. The plant exhibits exceptional tolerance for a wide variety of soil types, including those that are poor, nutrient-depleted, or acidic. Once established, it is notably drought-tolerant, making it a low-maintenance option for remote locations.
As a member of the legume family, crown vetch participates in nitrogen fixation, a symbiotic process where bacteria within its root nodules convert atmospheric nitrogen into a form usable by plants. This biological trait allows it to enrich the soil, which is a significant advantage in areas where topsoil quality is low. The plant also offers some secondary benefits, such as providing palatable, high-quality forage for livestock and wildlife, including deer and elk, with little bloat hazard.
The deep-green foliage and profuse, aesthetically pleasing flower clusters add an ornamental value, which was a factor in its adoption for highway beautification projects. The plant is cold-tolerant and resistant to browsing by deer and rabbits, enhancing its durability in various climates and environments. Its spreading growth habit can also provide good cover for ground-nesting birds.
Ecological and Horticultural Concerns
Despite its utility, the drawback of crown vetch is its highly invasive nature, which has led to its classification as a noxious weed in many regions. The plant spreads aggressively through both prolific seed production and extensive underground rhizomes. These robust, multi-branched rhizomes can grow horizontally up to 10 feet, allowing a single plant to rapidly cover a large area.
The dense, sprawling mats formed by crown vetch create a heavy canopy that effectively shades out and suppresses native vegetation. This displacement of local flora severely reduces species diversity and degrades wildlife habitat. This unchecked growth can lead to the formation of monocultures, where the plant becomes the sole dominant species in an area.
The nitrogen-fixing ability, while beneficial in poor soils, can alter the nitrogen cycle of native ecosystems that depend on low-fertility conditions. Crown vetch also contains compounds toxic to non-ruminant animals, such as horses, if consumed in large quantities, though it is generally safe for cattle. Furthermore, its dense cover can mask underlying soil problems, concealing rill and gully erosion on steep slopes instead of fully preventing it.
Strategies for Control and Eradication
Managing established crown vetch populations is a challenging and often long-term commitment due to its deep and extensive root system. Manual removal is generally ineffective for large infestations because it is nearly impossible to extract all the rhizome fragments, and any remaining piece can easily resprout. For small, new patches, hand-pulling can be attempted, ensuring that as much of the root material as possible is removed.
Mechanical control through repeated mowing can help suppress the plant’s vigor and prevent seed production. Mowing should be conducted multiple times throughout the growing season, typically starting in late spring, and must be repeated for several consecutive years to deplete the plant’s energy reserves. Prescribed burning is another method that can suppress above-ground growth and kill new seedlings, but established plants will quickly resprout, often requiring integration with other techniques.
The most effective method for controlling large, dense infestations is the application of systemic herbicides. Herbicides like glyphosate, triclopyr, and clopyralid have shown efficacy against crown vetch. Selective herbicides, such as triclopyr or clopyralid, are often preferred in areas with desirable native grasses because they target broadleaf plants, minimizing damage to surrounding non-target species. Herbicide application is best timed for the plant’s period of active growth, in early spring or late summer, and requires repeated treatments over several years for complete eradication.