Somerset County

Robinia pseudoacacia   

Plant of the Week... 

...or Black locust is a native tree that grows in dry to medium well drained soil and prefers to grow in full sun.  They can tolerate a wide range of soil types from sandy soils to moist, organically rich soils and the roots can fix nitrogen in the soil, which allows it to be planted to reclaim soils in abandoned sites.  Plants are cold tolerant from USDA zones 4-8, and as fast growers, can quickly create thickets.   Black locust can grow 30-50 feet tall and 20-35 feet wide and spreads by root suckers and self-seeding.  Its silhouette is a columnar tree with an oval crown.  In May the plants bloom with fragrant, wisteria like flowers that cascade in 5-8-inch-long clusters which attract bees, who use the flower nectar to create delicious honey.   Each 1-inch white flower blooms for 7-10 days.   The leaves are attached alternately on the stems and are pinnately compound with 23 leaflets that can grow 8-14 inches long. Each leaflet is rounded with an entire margin and a dark blue green in color.   The stems zigzag with the alternating leaves, and are armed with spiny, paired prickles that grow ¼ to ½ inches long at each node.  The flowers mature into smooth, flat seed pods that are purple black in color in July and can stay on the trees through the winter.  There are 4-8 reddish brown seeds per pod, each shaped like a kidney bean.  Black locust is a larval host for many different butterflies like the Clouded Sulphur, Zarucco Duskywing, and the Silver-Spotted Skipper.  Bees love the flowers while birds love the leaf cover, and rabbits feed on seeds and sprouts during the winter. The plant is poisonous to humans, livestock and pets.  Insect pests include locust borer which can be fatal,  locust leaf miner, caterpillars, scale, weevils and whiteflies.  Disease can include canker, leaf spots powdery mildew, verticillium wilt and wood rot. 

Ginny Rosenkranz

Extension Advisory Committee