Black locust (Robinia pseudoacacia) is a fast growing tree native to the Allegheny Mountains of Pennsylvania. A member of the legume family (Fabaceae) family, black locust is hardy in USDA zones 3 to 8. Growing to a height of 30 to 50 feet at maturity, black locust has very fragrant creamy white flowers that bloom from May to June that resemble wisteria and pinnately compound leaves. It prefers sun and tolerates sandy dry soils and will grow in difficult conditions where other trees might not thrive.
Black locust sends up root suckers, which is why it is often seen growing in large thickets and the fragrance of the flowers permeates the air at bloom time. To prevent black locust from spreading the suckers must be removed or mown down on a regular basis. Black locust has large thorns and is not a tree for those who prefer maintenance free landscapes as it produces large brownish purple seedpods, 4 to 5 inches long.
Once widely planted for its soil stabilizing properties and extremely hard wood, which was used to make fence posts, black locust has become naturalized throughout the United States and many parts of the world. Black locust is one of those species that is a native plant, but is considered invasive when it is planted out of its range and is listed as invasive, not banned in Connecticut and prohibited in Massachusetts.