Black Locust
Identification & Biology
Photo By: Lisa Scott
Black locust
Black locust
Photo By: Lisa Scott
Black locust flowers
Black locust flowers
Photo By: Lisa Scott
Black locust flowers and seedpods
Black locust flowers and seedpods
Photo By: Lisa Scott
Black locust thorns
Black locust thorns
Photo By: Lisa Scott
Black locust bark
Black locust bark
Alias' :
False Acacia, Post Locust, Yellow Locust, White Locust, Green Locust
Latin Name :
Robinia pseudoacacia
Category :
Terrestrial Plants
Description :
- Deciduous tree that grows up to 25 m
- Thick, deeply grooved, grey-brown bark
- Seedlings have long sharp spines which are typically absent in mature trees
- Leaves are large, bright green and pinnate with paired leaflets
- Fragrant white flowers grow in drooping clusters
- Smooth dark red-brown seedpods
Black locust has been introduced across North America as an ornamental tree and to rehabilitate disturbed soil sites, such as mines. It mainly reproduces vegetatively through lateral roots forming dense, interconnected stands. Seedlings have high survivorship and fast growth rates, allowing them to rapidly dominate sites. Black locust also reproduces by seed with flowers blooming from April to June. Seedpods form in the fall and can persist through the winter, cracking open in the fall or spring. Seeds land and grow close to the parent tree but can be dispersed by wind, birds and other animals.
Black locust may be confused with honey locust (Gleditsia triacanthos), an introduced ornamental tree. When in bloom, black locust can be distinguished by its white flower clusters which are larger than the yellow-green flower clusters of honey locust. The spines of black locust are also much smaller than those of honey locust, growing up to 4 cm and 20 cm respectively. Spines are typically absent from mature black locust trees while honey locust spines persist into maturity.
Habitat
Black locust is native to the southeastern United States. It is now found throughout British Columbia, including the Okanagan and Similkameen valleys. Black locust prefers moist soils but can tolerate various soil conditions, including high acidity. It is intolerant of shade and grows best in open areas such as pastures, fields, forest edges, sloped hillsides, disturbed grasslands and roadsides.
Impact & Risks
- Can quickly form dense stands that outcompete and shade out native plants
- It is insect-pollinated and may divert pollinators away from native plants
- Black locust can increase the nitrogen, phosphorus and calcium in the soil, creating suitable growing conditions for other invasive plants
- Sharp spines on seedlings and young sprouts can be painful to touch
- Contains chemicals that are toxic to humans and horses
Prevention & Mitigation
The most effective way to ensure that your lands do not become infested with black locust is by prevention. Here are some recommendations to prevent invasion on your property:
- Do not purchase, trade or grow black locust
- Maintain your crops and natural lands in a healthy, vigorous condition to ensure a competitive plant community; competitive perennial forbs, shrubs and trees utilize water and nutrients that would otherwise be readily available for black locust
- Regularly patrol your property for black locust and immediately control or remove infestations before seed set
- Cooperate with adjacent landowners and encourage them to prevent black locust spread
- Immediately re-vegetate disturbed, bare soils with ecologically suitable species that provide dense, early colonization to prevent invasive plant establishment
- Do not move contaminated soils to a new area
Treatment & Disposal
- Do not attempt to hand-pull seedlings; black locust plants are connected by their roots and any root damage will cause stems to sprout
- Girdling can help to provide control with less regrowth than cutting; in the spring when trees are actively growing, manually cut away bark and cambial tissues around the trunks of trees as close to the ground as possible using an ordinary axe
- Large trees can be cut down and herbicides should be applied to the stump to prevent sprouts from re-growing; sprouts will need to be re-cut each growing season with additional herbicide application each year to be effective
- Chipping is an effective means of disposal for limbs and trunks
- Chemical control is also an option; before applying herbicides, read the label for full use and precautionary instructions
- For further information on the selection and application of chemicals to protect your crop, contact AgriService BC at 1-888-221-7141 or email AgriServiceBC@gov.bc.ca
- There are no biological controls (natural insect enemies) for black locust at this time
Okanagan Distribution
Priority Level Definitions
Watch For - Poses a significant threat (very high risk) and does NOT presently occur in the region OR is relatively new to the region and is very limited in extent.
High - High risk/impact; limited population with significant potential to spread in the region.
Medium - Medium risk/impact; limited distribution – broader population distribution with potential to spread further in a region.
Low - Low risk/impact; may be widespread or not, may be of concern in specific situations with certain high values – e.g. specific agriculture crops. Some species may be treated primarily with biological control agents.
