How to Identify Black Locust
Identify Black Locust by its greenish-golden heartwood, crisp ring-porous growth rings, heavy weight, and extreme hardness.
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Start with color. Black Locust heartwood is a distinctive greenish-yellow to golden-brown when fresh, aging to a warmer russet or reddish-brown, wrapped in a thin band of pale cream-to-yellow sapwood. That yellow-green cast in a heavy, hard board is a strong first clue — few domestic woods carry it. Under UV light or over time the heartwood shifts noticeably darker, which can distinguish an old board from a freshly cut one.
Read the end grain and pores. Black Locust is strongly ring-porous: each growth ring opens with a band of large, often plugged earlywood pores followed by very dense latewood, so the annual rings stand out crisply — the tight, distinct rings on our sample are typical. The earlywood pores are frequently occluded with yellowish tyloses, which contributes to the wood's water resistance and can give the pores a filmy, filled look under a lens. Rays are fine and not conspicuous.
Use weight and hardness as confirmation. Black Locust is genuinely heavy and very hard (Janka ~1,700 lbf) — it should feel dense in the hand, resist a fingernail or knife point, and dull tools quickly. A board that looks like ring-porous oak but is markedly heavier and harder is a good candidate for locust. Freshly cut, it can carry a faint sourish or slightly rank odor, milder than oak's tannic smell.
The main look-alikes are Honey Locust and the ring-porous oaks and Osage Orange. Honey Locust (Gleditsia triacantha) is a different genus and is typically pinkish-to-reddish rather than yellow-green, and is somewhat less hard and far less durable. Black and white oak share the ring-porous pattern but show large, obvious rays (prominent ray flecks on quartersawn faces) that Black Locust lacks, and oaks are lighter in weight. Osage Orange (Maclura pomifera) is even more vividly yellow-orange and slightly harder, but oxidizes to golden-brown much like locust, so a fresh cut showing bright orange points to Osage rather than locust. Mulberry is another yellow ring-porous look-alike but is softer and less dense.
Frequently asked questions
How do I tell Black Locust from oak?
Both are ring-porous with crisp growth rings, but oak shows large, conspicuous rays that produce prominent ray fleck on quartersawn faces, while Black Locust's rays are fine and inconspicuous. Locust is also heavier, harder, and carries a yellow-green tint rather than oak's tan-to-pinkish brown.
What's the difference between Black Locust and Honey Locust?
They are different genera despite the shared name. Black Locust (Robinia) is greenish-golden and exceptionally rot-resistant; Honey Locust (Gleditsia) tends toward pink-to-red heartwood, is somewhat softer, and is not durable in ground contact. Color and decay resistance are the quickest tells.
Could my yellow board be Osage Orange instead of locust?
Possibly. A fresh cut is the key: Osage Orange is vivid yellow-orange when new and slightly harder, while Black Locust is more yellow-green. Both oxidize to golden-brown, so if it started bright orange it is likely Osage, and if greenish-yellow it is likely locust.
Why do the pores look filled or filmy under a lens?
Those are tyloses — bubble-like growths that plug the earlywood vessels. Black Locust's heavily occluded pores are part of why it resists water and decay so well, and they are a useful end-grain confirmation.
Black Locust identified by the community
Recent Black Locust samples identified with Wood Identifier.
