Tree Identification
print close window
Robinia pseudoacacia - Black locust
Pinnate and doubly- pinnate compound leaves.
Showy, fragrant flowers of black locust.
Close-up look of the 2-4 inch long seed pods.
Black locust on a reclaimed mine site near Ely, Minnesota.
Seed pods of black locust on the left compare to seed pods of honeylocust on the right.
A pink flowered variety of black locust.
Trunk of black locust with the bark furrowing as the stems mature.
Spines on black locust. Typically found on smaller, rapidly growing stems and on sucker growth.
Black locust seed in winter.
All Images By: Dave Hanson
  • Characteristics
  • Disease Management
Black locust or common locust is not a Minnesota native. The original range was in the south and east portions of the United States, however; it is has naturalized throughout much of the eastern United States including Minnesota.

As a landscape tree - black locust has its detractors since the species can aggressively colonize a site and is often used for site reclamation purposes where the species will perform well on very poor soils.
Medium tree height: 30-50'
Canopy spreads: 20-30', Oval to irregular crown.
Drought Tolerance: Tolerant
Shade Tolerance: Intermediate
Soil pH Tolerance: Tolerant to high pH
Poor Soil Drainage: Intermediate to flooding
Salt Tolerance:

 Tolerant of salt spray and Tolerant of soil salts.
An alternately branched tree with pinnately compound leaves. The compound leaves typically have 7-19 sub-opposite to alternate leaflets. The smooth margined leaflets are green in the summer and yellow in the autumn. Bark on the black locust is a darker gray-brown that separates into deep furrows of interlacing ridges. Between the ridges the color can be orangish. Black locust has showy flowers that are typically white, however there are varieties with pinkish flowers. The fruit pod is not that large. Compare the mature purplish-brown pods of honeylocust to the brown, much smaller (2-4 inches long by 1/2 inch wide) pods of black locust.

Black locust is available in the nursery trade. The traits of the varieties vary in foliage color ('Frisia' a variety with golden yellow foliage) and flower color ('Purple Robe' with a pinkish-rose flower).

Did you know
Even though black locust is an attractive tree with an attractive flower, it is considered invasive - in the wrong location in the landscape black locust will readily colonize an area. The bark is said to be toxic to livestock and humans.
DISEASE SYMPTOMS MANAGEMENT
Nectria canker, Nectria cinnabarina and Fusarium sp. Fungi
 Cankers develop as sunken areas originating from a wound or dead branch stub. Advanced cankers are visible as dark brown discolored bark with cracks at the margins. Yellow/orange, salmon/pink, or reddish fruiting bodies form on the cankered areas. Provide proper cultural care. Avoid stress and mechanical damage. Prune during extended dry periods, make proper pruning cuts. Remove and destroy infected branches during dry weather.

CHEMICAL: None.