Quick facts

Common name: black walnut

Scientific name: Juglans nigra

Family: Juglandaceae

Origin: non-native

Black walnut is a large, broadleaf tree which can reach 30–40m high. The tree gets its name from its dark, heavily ridged bark which occurs even when it is still young.

Look out for: the leaflets which have toothed edges. Crushed leaves have a strong smell.

Identified in winter by: the segmented pith, or spongy tissue, inside the twig. At their base, buds have horseshoe-shaped leaf scars, or marks, left by fallen leaves.

What does black walnut look like?

Black walnut leaves

Credit: STUDIO75 / Alamy Stock Photo

Leaves

Pinnate and larger than that of the common walnut (Juglans regia) with more leaflets. Individual leaflets are oval, pointed, irregularly toothed and hairy underneath.

Black walnut catkins flowers

Credit: David Hosking / Alamy Stock Photo

Flowers

Both male and female flowers appear from late May–early June. The male flowers are on 8–10cm-long catkins that droop from the branches. Female flowers appear in clusters.

Black walnut fruit

Credit: Nature Photographers Ltd / WTML

Fruits

In autumn, flowers turn to a brownish-green plum-like fruit. The brown nut is held inside this large semi-fleshy husk which is rougher than that of common walnut. The shells are notoriously hard to break; drying them out makes it easier to crush and open the shells.

Not to be confused with:

Common walnut (Juglans regia). Black walnut has a greater number of leaflets (7–9 pairs) with toothed edges. Black walnut leaflets are also generally smaller and narrower than those of common walnut.

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Did you know?

The nuts have a bitter taste if picked when the casing has hardened.

Where to find black walnut

Black walnut is native to eastern North America and was introduced to Europe in 1629. In Britain it thrives best in warmer regions towards the south. It prefers fertile, lowland soil and needs plenty of light.

Value to wildlife

Squirrels and some birds feed off the nuts while the flesh is still green and the husk easier to penetrate.

Mythology and symbolism

Black walnut is common in Native American creation myths.

Did you know?

The roots contain a growth-inhibiting chemical which prevents many other trees and plants growing near it. This is said to affect tomatoes and apples in particular.

Uses of black walnut

There are many medicinal uses for every part of the tree, including as a mosquito repellent, a dermatological aid, an anti-diarrhoeal medication, a laxative and treatment for parasitic worms. It has been used to relieve the symptoms of fever, kidney ailments, gastrointestinal disturbances, ulcers, toothache, syphilis and snake bites.

The fruit husks of the black walnut contain juglone – a compound that inhibits bacterial and fungal growth and may be valuable in controlling infections in humans. It is also being tested for its cancer-fighting properties.

Its timber is attractive and valuable. It is strong and durable, and the heartwood has a mottled effect. 

The seeds give out a dark-coloured dye which is still used in crafts.

Threats and conservation

A young tree can be devastated by the grey squirrel. It is also susceptible to walnut-leaf blotch.