96 Robinia pseudoacaciaCommon Names: black locust, false acacia, yellow locust Family: Fabaceae (bean Family)
Black locust is a deciduous tree of variable form ranging from small suckering clumps to tall individuals growing to 80 ft (24 m) in height and 1-2.5 ft (0.3-0.8 m) in diameter. The short trunk usually divides not far above ground into multiple stems to create an open oblong or columnar crown. The wood tends to be brittle and weak limbs often break off. On mature trees the dark gray or brownish bark is deeply furrowed and turns jet black when wet. Impressive thorns are often present on both young and old trees. The dark green compound leaves are alternate pinnate (like a feather) and about 12 in (30.5 cm) long with individual oval-shaped leaflets about 1.5 in (4 cm). The foliage doesn't put on much of an autumn show, usually just turning dry and brown and before falling from the tree (it's not unusual for insect and disease to destroy them during the summer).
The black locust reseeds easily in almost any kind of soil. They grow rapidly to create populations in disturbed soils and waste areas. For this reason black locust is considered a weed tree in many areas. The fact that it is also a rather messy tree that drops twigs and large crops of seed pods discourages its planting as a yard tree. Several selections of black locust are available that mitigate these negative traits by not producing many flowers and hence fewer messy seedpods: 'Aurea' has yellow leaves and is breathtaking when planted against a backdrop of darker foliage trees; 'Frisia' has new foliage that is yellow and turns orange in fall; and 'Umbraculifera' is compact with a rounded crown that is sized for home landscapes. Unlike the species and other cultivars, 'Tortuosa' is slow growing with twisted gnarly branches like a yard-sized bonsai.
The black locust, Robinia pseudoacacia, is native to the central and eastern United States. It is widely planted in temperate climates around the world where it has naturalized in some places including parts of the Pacific northwest and Europe.
CultureThe black locust is adaptable to almost any soil condition except for poorly drained, heavy-textured soils (clays). Remove suckers in autumn to maintain single trunk trees. Light: Full sunlight preferred but will grow in partial sun. Moisture: Drought tolerant. Hardiness: USDA Zones 4 - 9. Propagation: By root suckers and hardwood cuttings. Seeds must be scarified to germinate.
It is planted widely for wind breaks and erosion control projects. The black locust, and especially its cultivars, are commonly used as an ornamental inside and outside of its normal range. It is a good choice for natural landscapes and wildlife landscapes as the seeds are eaten by many species of birds and bees have a preference for the fragrant flowers. This tree is useful in land reclamation and as a temporary tree to stabilize and enrich the soil while longer lived but slower growing species establish themselves.
Locust is a legume, which means that it has the ability to fix nitrogen from the air with the aid of nitrogen fixing bacteria on its roots. As a result of this ability, it grows readily in poor infertile soils. Not only does it not require nitrogen fertilization to grow, this tree can act as a natural supplier of nitrogen to other plants in the landscape.
The highly durable wood of this tree is used extensively for fence posts, wooden pegs, and ships timbers. When I was in grade school, the nuns had us make crowns of black locust thorns at Easter and the coolest (cruelest?) crown was set by a crucifix during Holy Week. An interesting side note is that the loosing crowns made awesome weapons when thrown like a Frisbees® and were capable of penetrating corduroy and drawing blood.
Steve Christman 8/12/97; updated 4/25/05, 4/28/12