Walnuts are a popular ingredient in many culinary traditions and a nutritious snack. Found in baked goods, salads, and as a standalone treat, their widespread use often prompts curiosity about their origin and the trees that produce them.
The Walnut Tree Species
Walnuts originate from trees in the Juglans genus. Two species are primarily responsible for commercially available walnuts: the English walnut (Juglans regia) and the Black walnut (Juglans nigra). The English walnut, also known as the Persian walnut, originated from southeast Europe to southwest China, with Persia being a significant domestication center. English merchants played a key role in distributing this species globally, earning it its “English” designation.
English walnuts are valued for their mild flavor and thinner, easier-to-crack shells. In contrast, the Black walnut (Juglans nigra) is native to eastern North America. This species is cultivated primarily for its valuable, dark timber, prized in woodworking. While edible, Black walnuts have a bolder, earthier flavor and an exceptionally hard, thick shell, making extraction challenging. Though less common in commercial nut production, Black walnuts offer higher protein.
Characteristics and Cultivation
Walnut trees are deciduous and can reach impressive sizes. English walnut trees grow up to 35 meters (115 feet) tall with a broad crown, while Black walnuts reach 30 to 40 meters (100-130 feet). A defining feature is their pinnately compound leaves, with multiple leaflets along a central stem. English walnuts typically have 5 to 9 leaflets, while Black walnuts have 9 to 23. Crushed English walnut leaves may emit a polish-like scent, whereas Black walnut leaves have a more pungent aroma.
Young English walnut bark is smooth and olive-brown, developing fissures and turning silver-grey with age. Black walnut trees have dark, deeply furrowed, ridged bark, often with a distinctive diamond-shaped pattern. The edible walnut is not a true botanical nut but a drupe: a fleshy fruit with a hard inner shell containing a seed. It begins as a green outer husk that encloses the hard, wrinkled shell. As it ripens, usually in autumn, the husk splits, allowing the nut to fall.
Walnut trees thrive in specific environmental conditions. They prefer well-drained, fertile, moisture-retentive loamy soils with a pH from slightly acidic to neutral (6.0-7.5). Full sun exposure is essential, and they should avoid frost pockets or overly exposed sites that can damage flowers and foliage. Harvesting occurs from late August through November, when husks begin to split. Nuts are collected from the ground after falling or are mechanically shaken. After collection, husks are removed, and nuts are dried for storage or processing.