Black locust is a deciduous tree and member of the pea family, Fabaceae, that also includes lupine, mimosa, and baptisia. It is native to the Allegheny Mountains , but invades dry or moist open woodlands, pastures, thickets, streamvalleys and roadsides and is now found in all states except Alaska and Hawaii. Trees are fast growing and sucker readily so can form colonies and dense thickets that exclude other vegetation. Tolerant of lean soil and urban pollution, black locust thrives in difficult sites. USDA Hardiness zone 3-8
Description: Growing 20-100′ tall, black locust has a straight trunk and rope-like dark gray bark. Although it can be somewhat untidy in appearance it has attractive creamy-white, fragrant flowers that are borne in pendulous clusters up to 8” long in late spring. Flat, purple-brown seed pods 4-5” mature in fall, turn brown, and persist into winter. The dull blue-green leaves have a pair of short spines at their base, are 6-14” long, and pinnately compound with up to 23 leaflets. Fall coloration is dull yellow and not attractive.
Control: Because of its rapid growth and suckering, black locust is difficult to control. Plants are shallowly rooted so hand pulling seedling can be effective if the entire root is removed. Cutting or burning young or mature plants often stimulate resprouting and suckering and is therefore counterproductive. Repeated cutting or mowing may control populations of the tree but will not eradicate them. The use of herbicides may be necessary. Triclopyr is more effective the glyphosate but both can be used as basal bark applications to live young standing trees from late summer to winter, as applications to freshly cut stumps, and or as a foliar spray when the leaves are fully expanded.