Common Name: Black Walnut

General Information

Juglans nigra is a deciduous tree with a wide-spreading crown; it usually grows up to 40 metres tall, exceptionally reaching 50 metres, with a tall, straight trunk[, ].
A multi-purpose tree, the black walnut produces an edible seed and a wood of high quality that is possibly the most sought after timber in N. America, The tree is often cultivated for its seed and timber and is also commonly used for a wide range of medicinal and other uses. The tree is also grown as an ornamental[].
Juglans nigra has an extensive range and a large, stable population. The plant is classified as 'Least Concern' in the IUCN Red List of Threatened Species(2013)[].

Known Hazards

The plant has occasionally been known to cause contact dermatitis in humans[].

Botanical References

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Range

Eastern N. America - South Dakota, Minnesota, Ontario, New York and Massachusetts, south to Texas and Florida

Habitat

A canopy tree in rich fertile woods and hillsides[, ], growing in deep well-drained soils; at elevations up to 1,000 metres[, ]. Plants can form pure stands or be in association with several other hardwood species[].

Properties

Conservation Status	Least Concern
Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Deciduous Tree
Height	30.00 m
Growth Rate	Fast
Pollinators	Wind
Self-fertile	Yes
Cultivation Status	Cultivated, Ornamental, Wild

Cultivation Details

The black walnut grows best areas with an annual precipitation from 30 to 130cm, an annual temperature in the range of 7 to 19°C and a pH from 4.9 - 8.2[]. The dormant plant is very cold hardy, but the young growth in spring, however, can be damaged by late frosts.
Requires a deep well-drained loam and a sunny position sheltered from strong winds[, ]. Prefers a slightly alkaline soil[]. Plants are best suited to deep, rich, slightly acid or neutral soil, with good drainage, but will not grow well on infertile upland soil or on soils with poor drainage[].
The Black walnut is one of the most valuable natural forest trees in the United States[]. A very ornamental and fast growing plant[, ], it is sometimes cultivated in N. America for its edible seed.
Whilst potential yields of 7.5 tonnes per hectare have been postulated, it is more feasible to expect annual yields of around 2.5 tonnes per hectare[].
Good seed crops are usually produced every other year, though some plants fruit well annually whilst others produce god crops every third year[]. The average weight of a seed from wild trees is about 17g, though there are many named varieties and the weight of their seeds varies from 20 - 30g[, ].
There are breeding programmes that are seeking to develop cultivars with thinner shells[].
Trees in the wild commence bearing seeds when about 12 years old[]. Black walnut trees mature their fruit rather generally throughout the plants natural range where there is a growing season of about 150 days and an average summer temperature of 16.5°C[]. Trees do not fruit very freely in Britain unfortunately[, ]. They grow well in the eastern half of the country but often do not thrive in the west[]. Trees have been extensively planted for timber in parts of C. and E. Europe[].
This species hybridizes with Juglans regia[], some named cultivars have been developed from this cross for their seed.
Plants produce a deep taproot which makes them very drought resistant when established, though they are intolerant of root disturbance[, , ]. Seedlings should be planted out into their permanent positions as soon as possible and given some protection for their first winter or two since they are somewhat tender when young[, ].
Flower initiation depends upon suitable conditions in the previous summer[]. The flowers and young growths can be destroyed by even short periods down to -2°c, but fortunately plants are usually late coming into leaf[].
The black walnut is self-fertile, but the sequence of male and female blooming, called dichogamy, can and often does minimize chances of a tree shedding pollen on its own pistils. In different trees pollen may be shed before the receptivity period of female flowers, or at same time, or after pistil receptivity. For greatest possible nut production, plant trees of 2 or more cvs, as different cvs have overlapping pollen-receptivity periods and can pollinate each other[].
Any pruning should only be carried out in late summer to early autumn or when the plant is fully dormant otherwise wounds will bleed profusely and this will severely weaken the tree[].
Plants produce chemicals which can inhibit the growth of other plants. These chemicals are dissolved out of the leaves when it rains and are washed down to the ground below, reducing the growth of plants under the tree[, , ]. The roots also produce substances that are toxic to many plant species, especially apples (Malus species), members of the Ericaceae, Potentilla spp and the white pines (certain Pinus spp.)[]. Beans, peas and tomatoes are also particularly sensitive to these secretions and will not grow in the rooting zone[]. Trees cast quite a dense shade so, along with their other anti-social tendencies, are not very friendly trees for a woodland garden[].
The bruised leaves have a pleasant sweet though resinous smell[].

Edible Uses

Seed - raw or cooked. A sweet, rich distinctive delicious flavour it makes an excellent dessert nut and is also widely used in confections, cakes etc[, , , ]. The kernel is hard to extract and the oil it contains quickly turns rancid[, ]. The unripe fruits can be pickled[]. The fruit is borne singly or in pairs, it can be 35 - 80mm in diameter, containing a single, globose nut around 35 - 40mm in diameter[, , ]. The nuts can leave a permanent stain on clothing[].

An edible oil is obtained from the seed[, ]. A sweet taste but it tends to go rancid quickly[]. Used as a seasoning in bread, squash and other foods[].

The tree yields a sweet sap that can be drunk or concentrated into syrup or sugar[, , ]. It is tapped in spring.

Medicinal

The bark and leaves are alterative, anodyne, astringent, blood tonic, detergent, emetic, laxative, pectoral and vermifuge[, , ]. Especially useful in the treatment of skin diseases, black walnut is of the highest value in curing scrofulous diseases, herpes, eczema etc[]. An infusion of the bark is used to treat diarrhoea and also to stop the production of milk, though a strong infusion can be emetic[, ].
The bark is chewed to allay the pain of toothache and it is also used as a poultice to reduce the pain of headaches[, ].

The juice from the fruit husk is applied externally as a treatment for ringworm[, ]. The husk is chewed in the treatment of colic and applied as a poultice to inflammations[].

The burnt kernels, taken in red wine, are said to prevent falling hair, making it fair[].
Green husks are supposed to ease the pain of toothache[].

A tea made from the leaves is astringent[]. An infusion has been used to lower high blood pressure[]. It can be used as a cleansing wash[]. The pulverized leaves have been rubbed on the affected parts of the body to destroy ringworm[].

The oil from the ripe seeds has been used externally in the treatment of gangrene, leprosy, and wounds[].

The sap has been used to treat inflammations[].

Agroforestry Uses:

The leaves produce substances that depress the growth of other plants. These substances are washed onto the ground by rain and inhibit the growth of plants beneath the tree[, , ]. The roots also produce substances that are toxic to many plant species, especially apples (Malus species), members of the Ericaceae, Potentilla spp and the white pines (certain Pinus spp.)[].

Other Uses

A brown dye is obtained from the nuts, husks and bark[, , , ]. It does not require a mordant[]. The husks can be dried for later use[].
A brown dye is obtained from the leaves and stems[]. It does not require a mordant[]. The dye turns black if it is prepared in an iron pot[]. The leaves can be dried for later use[].
The husks are rich in tannin[].
The green fruit husks can be boiled to provide a yellow dye[].

The husks can be made into a high quality coal (does the report mean charcoal?[]) and is then used as a filter[]. It was used in gas masks[].

The shells may also be used in the automobile industry as a non-slip agent for tires and to protect gears and jet engines[].

The woody shells on the fruits have been used to make jewellery[].

An extract of the seed shell is used as an ingredient in commercial cosmetic preparations as an astringent, emollient and masking agent[].
An extract of the leaves is used as an ingredient in commercial cosmetic preparations as an astringent[].
An extract of the bark is used as an ingredient in commercial cosmetic preparations as a hair conditioner[].

Insects are said to avoid the walnut tree, hence it is often used as a poor man's insect repellent. When rubbed on faces, walnut leaves are said to repel flies[]. The leaves repel fleas and have been used as a strewing herb[, , ]. They are also used as an insecticide against bed bugs[]. The ground up husks are also insecticidal[].

An alternative ingredient of 'QR' herbal compost activator[]. This is a dried and powdered mixture of several herbs that can be added to a compost heap in order to speed up bacterial activity and thus shorten the time needed to make the compost[].

A very ornamental wood that is heavy, hard, strong, close-grained, very durable. Easily worked, it glues well, does not warp, shrink or swell much and takes a good polish. It weighs 38lb per cubic foot. A very valuable timber tree and possibly the most sought after wood in N. America, it is used in cabinet making, the interior finishes of houses, furniture, airplanes, ship building, veneer etc[, , , , , , , , , ].

Propagation

The seed is best sown as soon as it is ripe in individual deep pots in a cold frame[]. You need to protect it from mice, birds, squirrels etc. The seed usually germinates in late winter or the spring. Plant out the seedlings into their permanent positions in early summer and give some protection from the cold for their first winter or two.
The seed can also be stored in cool moist conditions (such s the salad compartment of a fridge) over the winter and sown in early spring but it may then require a period of cold stratification before it will germinate[, , ].