Key Facts
- Deciduous leguminous tree that fixes nitrogen
- Fast growing but relatively short lived for a tree
- Showy, fragrant clusters of white pea flowers in late spring
- Spreads by root suckers and can form dense thickets
- Wood is hard and rot resistant and used for posts and fuel
- Tolerates poor, dry, and alkaline soils but dislikes waterlogged sites
- Prefers full sun and flowers poorly in shade
- Considered invasive or naturalized outside parts of its native range
- Contains toxic compounds making seeds, bark and foliage hazardous if ingested
Black Locust Tree is a fast growing deciduous legume valued for fragrant white pea like flowers in late spring and hard, rot resistant wood. It fixes nitrogen and tolerates poor soils but spreads by root suckers and contains toxic parts so choose planting sites carefully.
Identification
Robinia pseudoacacia is a medium sized deciduous tree that typically reaches 30 to 50 feet tall and spreads 20 to 35 feet. It is a legume that fixes nitrogen and produces showy, fragrant clusters of white pea like flowers in late spring. The wood is hard and rot resistant and has traditional uses for posts and fuel.
Where to grow and best uses
Plant Black Locust in full sun for best flowering and form where quick shade, timber or wildlife value is wanted. It tolerates poor, dry and alkaline soils and performs on rocky sites. Avoid planting near small garden beds or sensitive native stands because it naturalizes and can form dense thickets from root suckers.
Planting and spacing
Place trees where they have room to develop a canopy and to limit suckering. Use spacing that reflects a mature spread of about 20 to 35 feet between trees to prevent crowding and thicket formation. Siting in well drained soil is critical because waterlogged conditions cause decline.
Watering and soil
Black Locust prefers well drained loam to sandy soils and tolerates poor and dry conditions as it establishes. Avoid poorly drained or waterlogged sites because standing water often leads to decline. Once established the species shows good tolerance of dry soils but will not thrive in consistently wet ground.
Maintenance and after flowering care
Prune to remove crossing limbs and to manage structure, keeping the canopy open for good flowering. Coppicing and stump sprouting are common responses to cutting and can be used to produce poles or fuelwood. Monitor and remove root sprouts from around the base to limit unwanted expansion.
Spread, naturalizing and control
Black Locust spreads by root suckers and can form dense clonal thickets that crowd out other plants. Control requires prompt removal of suckers by cutting or digging and sustained follow up because roots resprout. For region specific management requirements consult local extension or invasive species authorities before planting.
Toxicity and pets
The species contains toxic compounds and seeds, bark and foliage can be poisonous to humans, livestock and pets if eaten. The ASPCA and university extension sources list Robinia species as toxic. If ingestion is suspected contact poison control or a veterinarian for guidance rather than waiting for signs to appear.
Propagation
Black Locust reproduces readily by seed and by vegetative means including root suckers, root cuttings and stump sprouts. Stem cuttings and coppicing are also used. Propagation success and sucker vigor vary by cultivar and site so plan containment or frequent removal where spread is undesirable.
Frequently asked questions
- How fast does Black Locust Tree grow?
- It is fast growing for a tree and commonly reaches 30 to 50 feet within a few decades.
- Is Black Locust toxic to pets?
- Yes. Seeds, bark and foliage can be poisonous to pets and livestock. Contact a veterinarian or poison control if ingestion occurs.
- Does Black Locust sucker and spread?
- Yes. The tree reproduces by root suckers and can form dense clonal thickets if not managed.
- What soils does it prefer?
- It prefers well drained loam to sandy soils and tolerates poor, dry and alkaline conditions but avoids standing water.
- How tall does Black Locust grow?
- Typically 30 to 50 feet tall, occasionally taller in favorable sites.
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