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Black locust (Not recommended)

Robinia pseudoacacia

Common names:
black locust, common locust

Content Detail

Black locusts have invasive traits that enable them to spread aggressively. While these trees have demonstrated invasive traits, there is insufficient supporting research to declare them so pervasive that they cannot be recommended for any planting sites. Review of the risks should be undertaken before selecting these trees. Black locust produces hanging clusters of very fragrant white flowers in spring. This fast-growing native tree can form colonies and has brittle wood. Sharp spines may be present, especially on sucker growth. They are also susceptible to locust borers.

  • Family (English) Pea
  • Family (botanic) Fabaceae (formerly Leguminosae)
  • Tree or plant type Tree
  • Foliage Deciduous (seasonally loses leaves)
  • Native locale Illinois, North America
  • Size range Medium tree (25-40 feet), Large tree (more than 40 feet)
  • Mature height 30-50 feet
  • Mature width 20-35 feet
  • Light exposure Full sun (6 hrs direct light daily), Partial sun / shade (4-6 hrs light daily)
  • Hardiness zones Zone 4, Zone 5 (Northern Illinois), Zone 6 (City of Chicago), Zone 7, Zone 8
  • Soil preference Moist, well-drained soil
  • Tolerances Alkaline soil, Dry sites, Road salt
  • Season of interest late spring
  • Flower color and fragrance Fragrant, White
  • Shape or form Oval, Thicket-forming
  • Growth rate Fast
  • Transplants well Yes
  • Planting considerations Aggressive, Excessive sucker growth, Highly susceptible to ice damage, Messy fruit/plant parts, Weak wood and branch structure
  • Wildlife Insect pollinators
  • Has cultivars Yes

Native geographic location and habitat: 

Black locust is native to the eastern and the southern parts of the United States. In Illinois, it is native only to the far southern edge of the state.

Bark color and texture: 

The dark gray bark is deeply ridged and furrowed with a rough, scaly, or ropy texture.

Leaf or needle arrangement, size, shape, and texture:

Leaves are alternate and pinnately compound. The entire leaf can be up to a foot long. Each leaflet has a tiny point at the end. The leaves are bluish-green with very little color change in the fall.

Flower arrangement, shape, and size: 

The fragrant, creamy white flowers appear in hanging clusters in late May. Each cluster can be up to 8 inches long.

Fruit, cone, nut, and seed descriptions: 

The fruits are flat brown legumes (pods) and are 4 inches long.

Plant care: 

This species grows in a wide range of conditions, but avoid growing it in wet sites. It is best pruned in the dormant season as this tree will ‘bleed’ when pruned in spring.

List of pests, diseases, and tolerances:

Locust borer is a serious pest of black locust. The wood is weak and brittle making it subject to storm damage. This tree can sucker to the point of forming colonies. Black locust is resistant to black walnut toxicity.

Frisia black locust (Robinia pseudoacacia ‘Frisia’): 

This cultivar has yellow foliage and grows 40 feet high by 25 feet wide.

Purple robe black locust (Robinia pseudoacacia ‘Purple Robe’):

The flowers on this tree are deep rosy-purple. The new foliage emerges tinged with purple and matures to a bronze-green color.

Twisty Baby® black locust (Robinia pseudoacacia ‘Lace Lady’): 

At 20 feet high by 20 feet wide, this tree is smaller in size and has contorted limbs.

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