Robinia pseudoacacia, black locust
1 / 7
Broadleaf Deciduous Trees

Robinia pseudoacacia

black locust

Fabaceae

Central Appalachian and Ozark regions of eastern North America

At a Glance

TypeTree
HabitUpright
FoliageDeciduous
Height40-70 feet (12-21 m)
Width25-35 feet (7.6-10.7 m)
Maturity15 years

Growing Zones

USDA Hardiness Zones

3 - 8
Zone 3
Zone 4
Zone 5
Zone 6
Zone 7
Zone 8
These zones indicate the coldest temperatures this plant can typically survive.
Frost Tolerancehardy

Key Features

Attracts Pollinators
Attracts Butterflies
Deer Resistant
Drought Tolerant
Fragrant (strong)
Native to North America
Maintenancehigh

Overview

Robinia pseudoacacia is a medium to large deciduous tree reaching 40-70 feet (12-21 m) tall with a spread of 25-35 feet (7.6-10.7 m), developing an open, irregular crown with upright branching. Bark is dark gray to nearly black, deeply furrowed with interlacing, rope-like ridges — among the most textured bark of any North American tree. Branches and twigs bear paired stipular thorns, 0.5-1 inch (13-25 mm) long, at the base of each leaf. Leaves are alternate, pinnately compound, 8-14 inches (20-36 cm) long, with 7-19 oval leaflets, each 1-2 inches (2.5-5 cm) long. Foliage is bright to medium green, creating a fine-textured, light, filtered shade. Fall color is generally yellow-green, not a strong ornamental feature; leaves drop early. Flowers are white, fragrant, pea-like, 0.75-1 inch (2-2.5 cm) long, borne in pendulous racemes 4-8 inches (10-20 cm) long in May to June. Fragrance is intense, sweet, reminiscent of orange blossoms, carrying over considerable distance. Fruit is a flat, brown pod 2-4 inches (5-10 cm) long, persisting through winter. A nitrogen-fixing legume (Fabaceae) with Rhizobium root nodules. Growth rate is very fast at 24-36 inches (61-91 cm) per year. Trees are moderately short-lived at 60-100 years. Spreads by root suckers and prolific self-seeding; classified as invasive in parts of the Pacific Northwest, particularly on dry, disturbed sites west of the Cascades. Wood is extremely hard, dense, and rot-resistant. All parts except flowers are toxic, containing robin and robitin.

Native Range

Native to the central Appalachian and Ozark regions of eastern North America, from Pennsylvania south to Georgia and west to Missouri and Oklahoma. Original native range is relatively restricted but has expanded dramatically through naturalization. Classified as invasive in multiple Pacific Northwest counties, particularly on disturbed, dry sites.

Suggested Uses

Planted on difficult sites where other trees fail, including dry slopes, disturbed ground, mine reclamation sites, and poor urban soils, spaced 25-35 feet (7.6-10.7 m) apart. Nitrogen fixation improves degraded soils. Extremely durable wood is valued for fence posts, outdoor furniture, and boat-building. Check local invasive species regulations before planting. Thornless and non-suckering cultivars ('Umbraculifera', 'Lace Lady') are more appropriate for residential settings.

How to Identify

Identified by deeply furrowed, rope-like dark bark, paired stipular thorns at leaf bases, pinnately compound leaves with 7-19 small oval leaflets, and pendulous racemes of fragrant white pea-like flowers. Fruit is a flat brown pod persisting into winter. Distinguished from Gleditsia triacanthos (honey locust) by smaller, fewer leaflets (not bipinnately compound), white (not greenish) flowers, and shorter thorns. Distinguished from Robinia pseudoacacia 'Frisia' by green (not golden-yellow) foliage.

Appearance

Size & Dimensions

Height40' - 70'
Width/Spread25' - 35'

Reaches mature size in approximately 15 years

Colors

Flower Colors

white

Foliage Colors

green

Fall Foliage Colors

yellow

Bloom Information

Bloom Period

~2 weeks
J
F
M
A
M
J
J
A
S
O
N
D
Spring
Fragrant white pea-like flowers in pendulous racemes appear in May to June, lasting 1-2 weeks. In the Pacific Northwest, bloom typically occurs in late May to early June. Fragrance is intense and sweet, detectable from considerable distance. Flowers are highly attractive to honeybees; black locust honey is prized. Flat brown pods persist through winter.

Detailed Descriptions

Flower Description

White

Foliage Description

Bright to medium green

Growing Conditions

Sun Requirements

Full Sun
Requires 6-12 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range5.0 - 8.5(Neutral)
357912
Soil Types
loamsandclayrockychalk
Drainage
well drained

Water & Climate

Water Needs

Very Low

Frost Tolerance

hardy

Time to Maturity

5-8 years

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Water during the first growing season only. Established trees are extremely drought-tolerant and require no supplemental care. Plant in full sun with at least 6 hours of direct light. Tolerates a very wide range of soil types including poor, dry, rocky, alkaline, and compacted soils. As a nitrogen-fixing legume, improves soil fertility. Check local invasive species regulations before planting — classified as invasive in parts of the Pacific Northwest. Root suckers and prolific seeding can create management challenges. Locust borer (Megacyllene robiniae) is the primary pest, tunneling in trunks and causing structural weakness; maintain tree vigor to reduce susceptibility. Locust leaf miner causes cosmetic browning of foliage in midsummer.

Pruning

Prune in late winter (January through February) while dormant. Remove dead, damaged, and crossing branches. Branches are brittle and prone to breakage in storms. Remove root suckers regularly to prevent colony formation. Avoid heavy pruning, which stimulates vigorous suckering. Thorns on young growth require protective gloves.

Pruning Schedule

J
F
M
A
M
J
J
A
S
O
N
D
winter

Maintenance Level

high

⚠️ Toxicity Warning

Toxic to pets and humans