Black Locust

Geographic Distribution

Black Locust is a North American native tree that despite its relatively small endemic area has been widely planted throughout the United States and Canada for its rapid growth and resistance to drought conditions.  For the botanically inclined, Black Locust is known as Robinia pseudoacacia.

R. pseudoacacia is native to several small and currently separated areas of North America, although in the past the native area is likely to have been contiguous, yet no one knows for certain what this larger native area was exactly comprised of. The eastern section is centered in the Appalachian Mountains and ranges from central Pennsylvania and southern Ohio, south to northeastern Alabama, northern Georgia, and northwestern South Carolina. The western section includes the Ozark Plateau of southern Missouri, northern Arkansas, and northeastern Oklahoma, and the Ouachita Mountains of central Arkansas and southeastern Oklahoma. Outlying populations appear in southern Indiana and Illinois, Kentucky, Alabama, and Georgia.  My example originated from southern Missouri.

Black Locust Exterior

Black Locust Exterior

As mentioned before, despite its relatively small native zone, R. pseudoacacia have been widely planted elsewhere and currently it is reported as growing in all of the lower 48 United States as well as in British Columbia, Ontario, Quebec, New Brunswick, Nova Scotia, and Prince Edward Island in Canada.

While once widely planted, in some instances R. pseudoacacia have become classically invasive and one should think carefully before planting such a vigorously growing and self-seeding tree into a non-native landscape.

One must always be careful to distinguish between R. pseudoacacia (Black Locust) and Gleditsia triacanthos (Honey Locust).  Despite the similar common names, these trees of are of completely different genus designations and the wood itself does not look or behave similarly either.

For sake of simplicity, I will simply refer to Black Locust from this point forward.

General Characteristics

The wood of the Black Locust tends toward a color range moving from the palest yellow-green tone to a much darker brown color.  As is common in highly colored woods, this original coloration will tend to shift toward a darker russet brown color with age and exposure to ultraviolet light sources.

Based on appearance alone, Black Locust can easily be confused with both Osage Orange, Mulberry, or even Honey Locust in some circumstances.  If knowing the specific species is important to you, there are methods that can be used for differentiation, including the use of ultraviolet light fluorescence, present, for example in Black Locust but absent in Mulberry. The presence of a water-extractable pigment in Osage Orange that is absent in Black Locust, or Mulberry for that matter, will provide differentiation there as well.

Black Locust grain is usually straight while the texture is of a medium quality.

Black Locust Interior

Black Locust Interior

The end-grain of Black Locust appears porous in a ring format with both large and small pores depending on the stage of development.  Growth rings are distinct but rays are only barely visible even with a lens.

Black Locust is very durable in its ability to resist rot and it also displays quite good weathering ability, both of which lead to its use in outdoor applications including with ground contact such as fence posts.

Working Characteristics

The overwhelming characteristic about Black Locust that affects its workability is its hardness which leads to mixed results.  For example, while the grain is usually straight, the unusually high density and hardness can make it difficult to work with either hand or machine powered tools.  In addition, Black Locust will have a, perhaps predictably, moderate blunting effect on all cutting surfaces, so frequent resharpening, or the frequent replacement of disposable cutters, will be essential to success in working with Black Locust.