Black Locust

The Black Locust reaches a height of seventy feet, with a trunk three or four feet in diameter and brittle branches that form an oblong narrow head. It spreads by underground shoots. The leaflets fold together in wet weather and at night; some change of position at night is a habit of the entire leguminous family. Although similar in general appearance to the honey locust, it lacks that tree’s characteristic long branched spines on the trunk, instead having the pairs of short thorns at the base of each leaf; the leaflets are also much broader. Black locust has nitrogen-fixing bacteria on its root system; for this reason it can grow on poor soils and is an early colonizer of disturbed areas.

The LEAVES are parallel, compound, odd-pinnate, 21-40 inches long, with slender hairy petioles, grooved and swollen at the base. Leaflets petiolate, seven to nine, one to two inches long, one-half to three-fourths of an inch broad, emarginated or rounded at apex. They come out of the bud conduplicate, yellow green, covered with silvery down which soon disappears; when full grown are dull dark green above, paler beneath. Feather-veined, mid-vein prominent. In autumn they turn a clear pale yellow. Leafs out relatively late in spring. Stipules linear, downy, membranous at first, ultimately developing into hard woody prickles, straight or slightly curved. Each leaflet has a minute stipel which quickly falls and a short petiole.

The FLOWERS come out in May or June, after the leaves. Papilionaceous. Perfect, borne in loose drooping racemes four to five inches long, cream-white, about an inch long, nectar bearing, fragrant. Pedicels slender, half an inch long, dark red or reddish green. They are intensely fragrant (reminiscent of orange blossoms) and are considered edible (dipped in batter; deep-fried).

The FRUIT is a legume two-valved, smooth three to four inches long and half an inch broad, usually four to eight seeded. Ripens late in autumn and hangs on the branches until early spring. Seeds dark orange brown with irregular markings. Cotyledons oval, fleshy.

The BARK is dark gray brown tinged with red, deeply furrowed, surface inclined to scale. Branchlets at first coated with white silvery down. This soon disappears and they become pale green, afterward reddish brown. Prickles develop from stipules, are short, somewhat triangular, dilated at base, sharp, dark purple, adhering only to the bark, but persistent.

It is planted for firewood because it grows rapidly, is highly resilient in a variety of soils, and it grows back even faster from its stump after harvest by using the existing root system. The wood is extremely hard, resistant to rot and durable, making it prized for furniture, flooring, paneling, fence posts and small watercraft. With fertilizer prices rising, the importance of black locust as a nitrogen-fixing species is also noteworthy. The mass application of fertilizers in agriculture and forestry is increasingly expensive; therefore nitrogen-fixing tree and shrub species are gaining importance in managed forestry.