Black Walnut is an elegant tree yielding fine timber and edible nuts, equally at home in a large, sheltered garden or a mixed broadleaved forest. It was introduced to Britain and Ireland in the mid-seventeenth century (a neophyte) by John Tradescant the Younger (1608-1662).
Native to North America, including Ontario in Canada, and to central and eastern states in the USA, from the Great Lakes region south to the Gulf Coast, and west to Kansas.
Monoecious. Pioneer, fast-growing. Wind-pollinated. Seeds distributed by birds and mammals. Hybridises with other walnut species, including Common Walnut (Hybrid Walnut p. xxx).
Large (40-50m), strongly upward-branching, usually straight-trunked. Bark grey-brown, narrowly ridged in a lattice. Twigs downy, with notched heart-shaped leaf scars showing three dots and pale chambered pith. Foliage smells of juglone, citrus-spice. Leaves pinnate compound, 20-60cm, with 10-23 serrated leaflets, often lacking a terminal one, downy beneath. Fruit a tough-husked spherical drupe (3-4cm) staining hands black. Common Walnut differs: 5-7 leaflets, easily split husks.
Cold-hardy but frost-prone, thriving in deep, moist, fertile, neutral soils; avoid frost hollows and waterlogging. Light-demanding, preferring warm, sunny sites. An attractive open-grown ornamental needing space, though beware its allelopathic juglone (rhubarb is very sensitive). For timber, grow with non-competing companions such as Silver Birch, Small-leaved Lime and Wild Cherry, or nitrogen-fixers like alders. Prune side branches in July.
Juglone produced in leaves and roots is allelopathic, hindering growth from other plants nearby. No notable associations where introduced.
Although affected by various diseases, by far the most worrying is thousand cankers disease, present in North America and Europe (Italy) but so far absent from Britain and Ireland. Carried by the Walnut Twig Beetle (Pityophthorus juglandis), the fungus is fatal to walnuts, especially Black Walnut, killing mature trees in just 2-3 years, with symptoms of sudden leaf wilt and branch dieback.
An attractive ornamental, rarely grown here for fruit. Its timber is its greatest asset, second in beauty and quality only to Common Walnut, and one of few dark hardwoods growable in Britain and Ireland. Strong and shock-absorbing (favoured for gunstocks), with rich chocolate-brown heartwood and little sapwood, it polishes well and is prized in cabinet-making; in the USA it is commonly cut for veneers.
