The classification of wood as hardwood or softwood often creates confusion because the terms do not strictly refer to the material’s physical density. Many assume a “hardwood” must be physically hard, yet some softwoods are denser than certain hardwoods. Elm, prized for its distinctive grain and strength, frequently becomes a subject of this misunderstanding. Understanding Elm’s place requires separating its practical hardness from its scientific, botanical identity.
The Classification of Elm Wood
Elm, belonging to the genus Ulmus, is unequivocally classified as a hardwood. This determination is based on the tree’s fundamental biological structure. The classification places Elm alongside other broadleaf, flowering trees, regardless of whether the specific species yields a timber that feels relatively “soft” to the touch. This categorization is consistent across all species within the genus, including American Elm, Red Elm, and Rock Elm.
Understanding the Botanical Definition
The distinction between hardwood and softwood is rooted in the cellular structure of the wood itself. Hardwoods come from broadleaf, flowering trees, and their primary characteristic is the presence of specialized water-conducting cells called vessels, or pores. These vessels appear as small, circular openings when the wood is viewed in cross-section and are a defining feature of this group. Elm is considered a ring-porous wood, meaning its vessels are larger and more numerous in the earlywood, creating a distinct ring pattern.
Conversely, softwoods originate from non-flowering, cone-bearing trees, and their wood structure is simpler. They lack true vessels and instead rely on long, thin cells called tracheids to perform both water transport and mechanical support. Therefore, the botanical classification is a matter of anatomy, specifically whether the wood possesses these vessel elements.
Physical Characteristics That Define Elm
Elm wood’s physical properties contribute to the confusion surrounding its classification, as its hardness varies significantly between species. The Janka hardness rating, which measures the force required to embed a steel ball halfway into the wood, ranges from approximately 810 pounds-force (lbf) for English Elm to 1,320 lbf for Rock Elm. American Elm, a common species, registers around 830 lbf, placing it in the moderate or “soft hardwood” category, softer than woods like oak or maple.
A defining feature of Elm is its unique interlocked grain, where the wood fibers spiral and reverse direction as the tree grows. This structure makes the wood resistant to splitting and gives it exceptional shock resistance and bending strength. Due to this resistance, Elm has historically been used for demanding applications like wheel hubs, chair seats, and water pipes. It remains popular today for furniture and flooring accents.
The average dried weight of Elm is approximately 560 kilograms per cubic meter, which aligns with its moderate density. While the interlocked grain provides toughness, it simultaneously makes the wood challenging to work with, causing it to tear out easily during planing. This combination of moderate density, high toughness, and a striking, wavy grain pattern explains why Elm is frequently mistaken for a less durable wood.