Black locust (Not recommended)

Black locust has fragrant white flowers in spring.

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 risks should be undertaken before selecting these trees for planting sites. 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.

This plant has some cultivated varieties. Go to list of cultivars.

Botanical name:

Robinia pseudoacacia

All Common Names:

black locust, common locust

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:

  • Large tree (more than 40 feet),
  • Medium tree (25-40 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 (Chicago),
  • Zone 6,
  • Zone 7,
  • Zone 8

Soil Preference:

  • Moist, well-drained soil

Acid Soils:

  • Tolerant

Alkaline Soils:

  • Tolerant

Salt Spray:

  • Tolerant

Soil Salt:

  • Tolerant

Drought Conditions:

  • Tolerant

Poor Drainage:

  • Intolerant

Planting Considerations:

  • Aggressive,
  • Excessive sucker growth,
  • Highly susceptible to ice damage,
  • Messy fruit/plant parts,
  • Weak wood and branch structure

Ornamental Interest:

  • Spring blossoms,
  • Fragrant flowers,
  • Persistent fruit/seeds,
  • Showy flowers,
  • Attractive bark

Season of Interest:

  • Late spring

Flower Color & Fragrance:

  • Fragrant,
  • White

Shape or Form:

  • Oval,
  • Thicket-forming

Growth Rate:

  • Fast

Transplants Well:

  • Yes

Wildlife:

  • Insect pollinators

More Information:

Tree & Plant Care

This species grows in a wide range of conditions.  Wet sites should be avoided.
Best pruned in the dormant season as this tree will 'bleed' when pruned in spring.

Disease, pests, and problems

Locust borer is a serious pest of black locust.
The wood is weak and brittle, subject to storm damage.
This tree can sucker to the point of forming colonies.

Disease, pests, and problem resistance

Black locust is resistant to black walnut toxicity.

Native geographic location and habitat

Native to eastern and southern parts of the United States.  In Illinois, native only to the far southern edge of the state.

Bark color and texture 

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

Leaf or needle arrangement, size, shape, and texture

Leaves are alternate and pinnately compound, the entire leaf up to a foot long.  Each leaflet has a tiny point at the end.  Leaves are bluish green.  Very little color change in fall.

Flower arrangement, shape, and size

Fragrant, creamy white flowers in hanging clusters.  Each cluster can be up to 8 inches long.  Flowers produced in late May.

Fruit, cone, nut, and seed descriptions

Fruits are flat brown legumes (pods), 4 inches long.

Cultivars and their differences

Frisia black locust (Robinia pseudoacacia 'Frisia'):  Yellow foliage; 40 feet high by 25 feet wide.

Purple robe black locust (Robinia pseudoacacia 'Purple Robe'):  Flowers are deep rosy-purple; new foliage emerges tinged with purple and matures to a bronze-green color.

Twisty Baby® black locust (Robinia pseudoacacia 'Lace Lady'):  Smaller size tree (20 feet high by 20 feet wide) with contorted limbs.

 

 

Location of Robinia pseudoacacia (Black locust (Not recommended)) at the Arboretum