Black Locust
Robinia pseudoacacia
Overview
Present but not recommended for planting. Can be invasive and problematic. Valued for rot-resistant wood
Introduced from Appalachian region, widely planted for fence posts and erosion control. Now spreading into natural areas
Identification
Leaves
Compound leaves with 7-21 oval leaflets arranged along central stem. Light green color. Leaves emerge late in spring.
Bark
Deeply furrowed dark bark with thick ridges. Young branches have paired sharp thorns at leaf bases.
Flowers
Showy drooping clusters (racemes) of fragrant white pea-like flowers in late May-June. Very attractive to pollinators.
Fruit
Flat brown seed pods (2-4 inches) persist through winter. Seeds are toxic.
Growing Conditions
Climate
Well-adapted to Eastern Ontario climate but too adaptable - spreads aggressively
Hardiness Zones: 4a, 4b, 5a, 5b
Light Requirements
Soil
Moisture: dry, moist
Drainage: well-drained
pH Range: 4.5 - 8
Tolerance
Care & Maintenance
Pruning
Best Season: December-February
Frequency: Minimal pruning recommended
- Prune only when dormant in December-February
- Remove suckers regularly
- Wear heavy gloves due to thorns
- Avoid creating wounds that invite borers
Avoid: Growing season when borers are active
Watering
Establishment: Minimal watering needed even when young
Mature: Extremely drought tolerant
Seasonal Care Timeline
Spring
- Sucker control essential
- Leaf emergence late (don't mistake for dead tree)
- Thorns are hazard
Summer
- Beautiful fragrant flowers
- Locust borer active
- Remove suckers before they establish
Fall
- Leaf drop
- Seed pods persist
- Plan sucker removal
Winter
- Brittle wood breaks in ice storms
- Only season for pruning
- Thorns remain hazard
Common Issues
Aggressive Suckering
HighSpreads aggressively by root suckers, forming dense thickets
Symptoms: Numerous shoots from roots, Thicket formation, Difficulty controlling spread
Treatment: Regular removal of suckers, root barriers
Prevention: Not recommended for planting - consider removal
Locust Borer
HighBeetle larvae that tunnel in wood, can cause significant damage
Symptoms: Exit holes in bark, Sawdust, Branch breakage, Tree decline
Treatment: Difficult to control once established
Prevention: Maintain tree vigor, avoid wounding bark
Professional arborist recommended
Quick Facts
When to Call an Arborist
Recommended inspection: Annual inspection
- •Borer damage
- •Brittle branches breaking
- •Aggressive spreading
- •Tree near structures or natural areas
- •Consider removal due to invasive nature
Free consultation for Belleville residents
Recommended Services
Based on Black Locust characteristics