Black Locust

Black Locust (Robinia pseudoacacia) is a dense temperate hardwood cut from a medium-sized, fast-growing deciduous tree native to the Appalachians and the eastern and central United States. Though a legume rather than a true acacia, it is often sold in Europe under the trade name 'Robinia' or even 'Acacia,' where it is widely planted for durable outdoor timber.

At a glance the wood is heavy, tough, and strongly colored: a narrow band of pale cream-to-yellow sapwood surrounds a greenish- to golden-brown heartwood that darkens toward russet-brown with age and light exposure. The tight, distinct growth rings seen on our sample are a hallmark of this ring-porous species. Its combination of extreme hardness and outstanding natural decay resistance makes it one of the most durable domestic woods available.

The heartwood is a warm greenish-yellow to golden-brown when freshly cut, mellowing to a darker russet or reddish-brown as it oxidizes and weathers. The sapwood is thin and distinctly paler — light cream to pale yellow — giving a clear contrast against the heartwood core, exactly as on the sample. Grain is typically straight, the texture medium to coarse, and the wood carries a natural luster; the fine radial pattern and tight annual rings reflect its dense, slow-summerwood structure.

Black Locust is markedly ring-porous, with large earlywood pores that open each spring ring and dense latewood between them, which is what makes the growth rings read so crisply. It is a genuinely heavy, hard wood — roughly 770 kg/m³ air-dry, with a Janka hardness near 1,700 lbf, placing it well into the very-hard range, harder than white oak, hard maple, or hickory.

Its standout trait is durability: the heartwood is rated very durable to exceptionally durable, resisting rot, decay, and insect attack for decades in ground contact — among the best of any temperate hardwood. The pale sapwood is not durable and is usually trimmed away for outdoor uses.

Black Locust's legendary rot resistance makes it a first choice for outdoor and ground-contact work: fence posts, gate posts, stakes, decking, raised-bed and landscape timbers, boardwalks, and boatbuilding components (traditionally used for ship trunnels/treenails and small-craft framing).

Its hardness and toughness also suit it to flooring, tool handles, ladder rungs, mine timbers, railroad ties, and turned or bent items where strength matters. Historically it was prized for insulator pins and wagon parts. Increasingly it is used for outdoor furniture and decking as a domestic, sustainable alternative to tropical hardwoods like ipe or teak.

Black Locust is demanding to work because of its hardness and density. It is hard on cutting edges and can burn or blunt tools, so sharp carbide-tipped tooling, slow feeds, and patience help; it planes and turns to a smooth, lustrous surface when the tools are keen. It is very strong and stiff and steam-bends well. Pre-drilling is essential for nails and screws, as the dense wood splits and resists fastening.

Gluing can be somewhat difficult owing to density and natural oils, so surfaces should be freshly machined and clamped well. It finishes nicely and, given its durability, is often left unfinished to silver outdoors. Caution: Black Locust dust and its bark, leaves, and seeds contain toxic compounds (including the lectin robin and the glycoside robinin); the sawdust is a reported irritant and sensitizer, and the tree parts are poisonous if ingested, so use dust collection and a respirator and keep offcuts away from livestock.

Black Locust is moderately available in North America, more often as posts, landscape stock, decking, and turning blanks than as wide furniture lumber; clear, wide, defect-free boards can be harder to find because the tree is often small and can grow with sweep or borer damage. In Europe, plantation-grown Robinia is a well-established commercial timber and is more consistently sold as dimensioned lumber and decking.

Prices are moderate — generally more than common domestic softwoods but far less than imported tropical durables it competes with. The species is not CITES-listed and is not threatened; it is fast-growing, abundant, and often considered invasive outside its native range, so it is regarded as a sustainable, low-impact choice, and FSC-certified Robinia is available in Europe.