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TREES & plants

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.

 

 

Robinia pseudoacacia or Black locust (Not recommended)