Robinia pseudoacacia

The black locust is a deciduous, flowering tree in the Fabaceae or bean family. It may grow 30 to 50 feet tall, and 20 to 35 feet wide, and its trunk may measure up to 3 to 4 feet in diameter. While it is a native forest tree in the mountains of North Carolina, it is widely planted throughout the state and is now naturalized to all soil and water conditions, except for saturated soils. In other parts of the state, black locusts can be found in thickets, on clay banks, in waste areas, or along fence rows. Unfortunately, the black locust has become invasive in the Midwestern United States. It is a relatively short-lived tree with about a 90-year life span.

Black locust grows in a variety of soil types and can fix nitrogen in the soil, so it is sometimes used to reclaim soil banks in abandoned sites. This is a good plant for difficult sites, transplants well, and tends to reseed.  It develops shoots from roots.  It is moderately salt tolerant. Species trees are sometimes considered to be somewhat weedy. Trees send out long underground root suckers that not only become a maintenance problem but also can disrupt nearby gardening areas. The trees can be pruned and kept at shrub size by cutting them to the ground every 2-3 years, but pruning should be avoided in the spring as the tree will bleed.

The leaves are alternate, pinnately compound with 7 to 23 leaflets. The bark is gray or light brown, thick, fibrous, heavily ridged, and furrowed. In spring and early summer, fragrant, pea-like white flowers, borne in 5-inch long hanging clusters, mature. The tree produces a 2 to 4-inch flattened legume which contains 4 to 8 red-brown seeds.

This tree is rarely seen in residential areas and is not recommended for the home landscape because it tends to be invasive, weedy, suckering, thorny, and has brittle branches that can break off in the wind.

Seasons of Interest:

Bark:  Winter      Bloom:  Spring and Summer          Foliage:  Spring, Summer, and Fall    Fruits:  Fall

Quick ID Hints:

• 30 to 50 feet tall, and 20-35 feet wide, deciduous tree with erect, rounded, or oval habit
• bark is brown to gray, furrowed, and scaly
• dark blue-green, alternate, pinnately compound leaves with up to 23 lance or ovate-shaped leaflets
• fragrant white pea-like blooms, borne in 5 to 8-inch clusters, blooming from April to June
• fruits are smooth, flat, purple-brown seed pods, up to 4-inch long, seen from July to November, and may persist through winter

Insects, Diseases, or Other Plant Problems:   It is susceptible to locust borer (often fatal) and locust leaf miner (brown foliage). Other insect problems include caterpillars, weevils, scales, and whiteflies. Possible disease problems include canker, powdery mildew, leaf spots, wood rots, and verticillium wilt. Small branches of the Black locust fall easily during storms.  Some of its leaves are yellow and fall off during times of drought.

VIDEO created by Andy Pulte for “Landscape Plant Identification, Taxonomy and Morphology” a plant identification course offered by the Department of Plant Sciences, University of Tennessee.