Black walnut

Noyer noir

Juglans nigra L.Juglandaceae (walnut family)

Origin: Eastern North America (native in Ontario)


Black walnut is a large tree, with a rounded, open crown with some irregular branching.

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Leaves are pinnately compound with 14 - 23 leaflets, a terminal leaflet either absent or smaller than the others.

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Male and female flowers are borne separately on the same branch, the male flowers in dangling catkins.

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Fruits are round with a rough, aromatic, yellow-green husk, hanging in clusters of 1-3.

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Black walnut is a large tree, up to 30 m (98') or more tall, and up to 120 cm (47") in diameter, with a rounded crown.

The crown is open with some irregular branching

Young trees have light coloured scaly bark.

The bark of older trees is darker, often nearly black, with intersecting ridges.

Twigs are orange-brown, slightly hairy, with heart-shaped leaf scars.

The terminal bud is brown, hairy, slightly flattened, 8 - 10 mm (about 1/3") long.

Inside the twig there is an orange-yellow chambered pith.

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Leaves are pinnately compound, 20 - 60 cm (8" - 23") long, with 14 - 23 leaflets that are faintly hairy on the underside.

Leaflets are 5 - 13 cm (2" - 5") long, tapering to the tip and base, with fine toothed edges. Terminal leaflet either absent or smaller than the others.

Leaves have an alternate arrangement on the branch.

Leaves turn yellow in fall.

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Male and female flowers are borne separately on the same branch, emerging in May along with the leaves.

Tiny green male (pollen) flowers are borne in drooping catkins 5 - 12 cm (2" - 4 1/2") long.

Small red female (seed) flowers are borne in erect clusters of 1 to 4.

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Fruits are round with a rough, aromatic, yellow-green husk.

Fruits hang in clusters of 1 - 3.

The husk encloses a woody shell with smooth, rounded ridges and deep grooves on its surface that surrounds a sweet, oily walnut.

Some fruits drop in the fall while others may hang on the tree throughout winter.

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Black walnut is native to the deciduous forests of eastern North America and reaches the northern edge of its range in the Carolinian zone of southern Ontario. It has become naturalized in Manitoba and Quebec.

Derivation of names

The genus name Juglans means Jupiter's nut, from the Latin words Jovis, the god Jupiter, and glans, which means nut. The species name nigra is the Latin for black.

Commercial use

The wood of black walnut is highly prized for its density, strength, and colour. The wood is a deep, rich brown with an attractive grain and it does not easily warp. It has been used in shipbuilding and to manufacture veneer, gunstocks, and cabinet making. Because black walnut is coveted for its wood it has been over-harvested in the wild. Efforts to replant the species in Ontario are ongoing.

Wildlife value and human use

The sweet, oily nuts of black walnut are eaten by squirrels and humans. Because they perish quickly the nuts should be eaten soon after harvesting. Black walnut nuts are not those available commercially in grocery stores which come from English or Persian walnut (Juglans regia), introduced from Europe and Asia. Black walnut contains juglone, tanins and other compounds that produce a dark purple dye that was used by early settlers for dying hair and cloth and is still used in handicrafts.

Related species

Black walnut may be confused with both English walnut and the native butternut (Juglans cinerea). English walnut has only 5 - 9 smooth-edged leaflets per leaf, and greenish-brown twigs. Butternut has hairy leaves with a terminal leaftet as big as the adjacent pairs of leaflets. Its fruits are ridged, oval, pointed at the tip. The leaf scars are flat across the top.

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Black walnut IN TORONTO

Black walnut's place in Toronto's urban forest

Black walnut is rare in Ontario both because this is the northern limit of its range, and because it has been heavily harvested for its wood. It is often planted in Toronto's parks.

Landscape value and potential for home planting

Black walnut is a very large tree that requires a large space to grow. In addition, it exudes a toxin called juglone from its roots and fallen leaves that inhibits the growth of other plants around the tree, including its own seedlings, protecting itself from competition. Therefore, in a garden setting, any plants placed too close to a walnut won't grow. Juglone and other compounds leached from black walnut leaves and fruit will stain sidewalks and porches.

Black walnut is intolerant of shade. It grows best in deep, rich, moist soils. Dry soils may be tolerated but will cause the tree to grow slowly.

Pests and diseases: Black walnut may be attacked by walnut caterpillars or fall webworms, which feed on the leaves and can defoliate the tree. Black walnut is usually not seriously affected by other pests and diseases.

This tree is available for planting through LEAF's backyard tree program .

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WHERE CAN I SEE Black walnut?

Find trees on Tree Tour maps at Canadian Tree Tours:

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