WSU Clark County Extension

PNW Plants Searchable, categorized images

Black Locust

Scientific name: Robinia pseudoacacia

Type:Invasive plants
Plant Requirements
Zone:3 to 8
Sun:Full to partial sun
Plant Characteristics
Height:80 ft
Width:30 ft
Bloom:Showy flowers
Bloom Time:May
Bloom Color:White
Additional Characteristics



Wildlife value

Description Black Locust is a widely planted ornamental that has now escaped cultivation and become naturalized throughout eastern North America and parts of the West.

Black locust is a leguminous deciduous tree that grows from 30 to 80 feet tall. Leaves of black locust are arranged in a pinnate, alternate fashion with 7-19 leaflets. Leaves are 8” to 14” long.

Fragrant white flowers appear in drooping clusters in May and June and have a yellow blotch on the uppermost petal. Flowers are monoecious and perfect. They are showy and fragrant, white in color, 1” long and pea-like in appearance. Flower clusters are typically 5” long and hang in clusters. They appear in mid to late spring.

Fruit pods are smooth, 2” to 4” long, and contain 4 to 8 seeds. However a very thick seed coat hinders consistently successful seed germination.

The bark of the Black Locust is gray or light brown, thick and fibrous and heavily ridged and furrowed.

Black locust is an early successional plant, preferring full sun, well drained soils and little competition. It is commonly found in disturbed areas such as old fields, degraded woods and roadsides.

Root suckers easily arise from established root systems, sprouting new shoots and interconnecting fibrous roots to form extensive, dense groves of new plants.

Pest free in the Northwest.
For assistance, contact Dr. Charles Brun (, (360) 397-6060 5701
Computing and Web Resources, PO Box 6234, Washington State University, Pullman WA 99164-6234