The term “hardwood” often suggests wood that is dense and difficult to scratch. However, the scientific classification of wood is based purely on botanical origin, not physical hardness or weight. This distinction is relevant for species like locust, whose extreme physical performance can be counter-intuitive to its actual biological grouping. Understanding the difference between a botanically defined hardwood and a physically hard wood is key to correctly identifying locust timber.
Defining Hardwood and Softwood
The classification of wood into hardwood and softwood is rooted purely in how the parent trees reproduce. Hardwoods come from angiosperms, which are flowering plants that produce seeds enclosed in a fruit or shell, such as acorns or apples. These trees typically have broad leaves and are often deciduous, shedding their leaves seasonally. Hardwood structure is complex, featuring specialized vessel elements, or pores, that transport water.
Softwoods, by contrast, originate from gymnosperms, which are non-flowering, cone-bearing plants like pines, firs, and cedars. The term “gymnosperm” translates to “naked seed,” as their seeds are exposed on cones. Softwoods have a simpler cellular structure, primarily composed of tracheids, and lack the vessel elements found in hardwoods. This botanical grouping does not correlate perfectly with strength; for example, the hardwood balsa wood is softer than many softwoods.
The Botanical Classification of Locust
Both of the commercially relevant locust species, Black Locust (Robinia pseudoacacia) and Honey Locust (Gleditsia triacanthos), are classified as hardwoods. This classification is based on their botanical status as angiosperms, meaning they are flowering plants that produce enclosed seeds. Black Locust, for instance, produces fragrant white flower clusters and develops small, flat seed pods, confirming its place in the pea family (Fabaceae).
The Honey Locust also belongs to the Fabaceae family, producing less showy flowers and long, twisted pods, confirming its hardwood designation. Although these two species differ slightly in their physical characteristics, their foundational biology places them firmly within the hardwood category. This botanical classification resolves the common question, confirming that locust wood is scientifically a hardwood.
Practical Properties and Exceptional Durability
The confusion regarding locust’s classification stems from its physical properties, which are extreme even for a hardwood. Black Locust wood is known for its high density and strength, often exceeding that of species like oak. Its Janka hardness rating is approximately 1,700 pounds-force (lbf), making it substantially harder than many other common domestic woods. This density makes the wood highly resistant to denting and surface wear, desirable for heavy-use applications.
Beyond its hardness, the heartwood of the locust tree exhibits remarkable natural resistance to rot, decay, and insect damage. This durability is due to the presence of natural chemical compounds, such as flavonoids, which are deposited in the heartwood as the tree grows. This inherent resistance allows the wood to perform exceptionally well in harsh outdoor conditions without the need for chemical preservatives. The lasting power of locust wood has historically made it a preferred material for demanding uses like railroad ties, fence posts, and mine timbers.
The wood’s dimensional stability and minimal shrinkage upon drying further contribute to its reputation. Today, this combination of density, strength, and rot resistance makes it a popular choice for outdoor applications such as decking, outdoor furniture, and vineyard posts. Black Locust provides a durable, naturally long-lasting alternative to tropical hardwoods and chemically treated lumber for exterior construction.