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Loughmiller, Campbell and Lynn
Robinia pseudoacacia L.
Black locust, Honey locust
Synonym(s): Robinia pseudoacacia f. inermis, Robinia pseudoacacia var. pyramidalis, Robinia pseudoacacia var. rectissima
USDA Symbol: rops
USDA Native Status: L48 (N), CAN (I)
The largest representative of a mostly shrubby genus, black locusts become burly, pictureque mature trees 30-50 ft. or sometimes 70 ft., in height. Branching tends to fork and become crooked and limby. Branches and twigs with spines. Leaves divided into ovate to oblong leaflets up to 2 inches long and 1 inch wide, rounded at the ends and with smooth margins. Blue-green, feathery, pinnately-compound foliage contrasts well with the deciduous tree dark, furrowed bark. Fragrant, white, pea-like blossoms hang in pendulous clusters. Flowers appearing in April and May. Fruit a flat, straight to slightly curved pod up to 5 inches long.
British colonists at Jamestown discovered this species in 1607 and named it for its resemblance to the Carob or Old World Locust (Ceratonia siliqua L.). Posts of this durable timber served as cornerposts for the colonists first homes. Because this species is well-adapted to establishment in very poor soil, it has been widely used for land reclamation projects.
The eagerness of Robinia pseudoacacia to establish just about anywhere has a dark side; Black locust is often considered an invasive species and a garden thug because it spreads very rapidly by root sprouts and by the copious seeds it produces. Its wood, renowned for its toughness, belies its habit of shedding branches in high winds. Finally, its thorns are vicious to anyone attempting to work in or around the tree. This species and its various cultivars and hybrids should be rejected for most landscape uses because of the trees many bad habits.
Plant CharacteristicsDuration: Perennial Habit: Tree Leaf Retention: Deciduous Leaf Arrangement: Alternate Leaf Complexity: Pinnate Size Notes:
Green Fruit: Size Class:
Bloom InformationBloom Color: White
Bloom Time: Apr , May , Jun
, WY Canada: BC
, QC Native Distribution: GA
n. to PA, WV,
s. IL, LA
& e. OK; naturalized elsewhere Native Habitat:
Woods; thickets; fence rows
Growing ConditionsWater Use: Medium
Light Requirement: Sun
Soil Moisture: Dry , Moist
Soil pH: Circumneutral (pH 6.8-7.2)
CaCO3 Tolerance: High
Soil Description: Moist, rich to dry, rocky soils.
Black Locust is widely planted for ornament and shelterbelts. It is also used for erosion control, particularly on strip-mined areas. Although it grows rapidly and spreads by sprouts like a weed,
it is short-lived. Use Wildlife:
Flowers are a favorite of honeybees and hummingbirds. Use Other:
Virginia Indians made bows from the wood and apparently planted the trees eastward. Warning:
This species naturalizes easily and is considered an invasive weed
in many of its non-native areas of establishment. Its brittle branches (subject to breaking in winds), vicious thorns, rampant root sprouts and copious seeding make this species a garden thug. Conspicuous Flowers:
Birds , Butterflies , Hummingbirds Nectar Source:
PropagationDescription: Propagate by seed, spring root cuttings or dormant sucker divisions. Cuttings should be stored in cool, dry sand for three weeks before planting.
Seed Collection: Not Available
Seed Treatment: Mechanical or acid scarification or a hot water soak is necessary due to impermeable seed coats.
Commercially Avail: yes
National Wetland Indicator Status
This information is derived from the U.S. Army Corps of Engineers National Wetland Plant List, Version 3.1
(Lichvar, R.W. 2013. The National Wetland Plant List: 2013 wetland ratings. Phytoneuron 2013-49: 1-241). Click here
for map of regions.
Record Last Modified: 2011-04-15
Research By: TWC Staff