Common Name: Walnut

General Information

Juglans regia is a deciduous tree with a large, spreading, dense crown; it can grow up to 35 metres tall.
The walnut is an important food crop, being often cultivated on a commercial basis, both for its seed and for its valuable wood. The plant is also harvested from the wild for use as a food, as a popular traditional medicine and for a wide variety of other usesmedicine and source of materials. It is often cultivated as a food and timber crop, and is also grown as an ornamental.
Juglans regia has a wide range and probably also a large population. The plant is classified as 'Least Concern' in the IUCN Red List of Threatened Species(2017)[].

Known Hazards

None known

Botanical References

,

Range

Southeast Europe (Balkans), through western Asia (Turkey, Syria, Iran, Irag, Afghanistan)

Habitat

Forests in the Himalayas, preferring a northerly aspect in the west but a southerly or westerly aspect in the east of the range[].

Properties

Conservation Status	Least Concern
Edibility Rating
Medicinal Rating
Habit	Deciduous Tree
Height	20.00 m
Growth Rate	Medium
Pollinators	Wind
Self-fertile	Yes
Cultivation Status	Wild

Cultivation Details

Juglans regia is reported to tolerate an annual precipitation of 31 to 147cm, an annual temperature in the range of 7.0 to 21.1°C and a pH in the range of 4.5 to 8.2[]. The dormant plant is very cold tolerant, tolerating temperatures down to about -27°C without serious damage, but the young spring growth is rather tender and can be damaged by late frosts[]. Some late-leafing cultivars have been developed, these often avoid damage from spring frosts and can produce a better quality timber tree.
Requires a deep well-drained loam[] and a sunny position sheltered from strong winds. Prefers a slightly alkaline heavy loam but succeeds in most soils[, ].
The walnut tree is frequently cultivated for its edible seed in temperate zones of the world, there are many named varieties[, ].
Newer cultivars begin producing nuts in 5 - 6 years; by 7 - 8 years, they produce about 2.5 tons of nuts per hectare[].
Orchards on relatively poor, unirrigated mountain soil report 1.5 - 2.25 tonnes per hectare, orchards in well cultivated valleys, 6.5 - 7.5 tonnes per hectare[]. According to the Wealth of India, a fully grown individual can yield about 185 kg, but 37 kg is more likely[].
Trees grow well in most areas of Britain but they often fail to fully ripen their fruits or their wood in our cooler and damper climate[, ], they prefer a more continental climate. There are some very fine trees in Cornwall[]. Walnuts can produce large healthy trees in many parts of Britain, but seedling trees often do not fruit reliably. Some European varieties have been developed that succeed in colder areas[]. Seedling trees are said to take from 6 to 15 years to come into fruit from seed[], but these cultivars usually start cropping within 5 years.
Plants produce a deep taproot and 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. Some cultivars are self-fertile, though it is generally best to grow at least two different cultivars to assist in cross-pollination.
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.)[]. Trees have a dense canopy which tends to reduce plant growth below them[]. All in all, not the best of companion trees, it is also suggested that the trees do not like growing together in clumps[]. Trees are said to inhibit the growth of potatoes and tomatoes[].
Hybridizes with J. nigra[].
This species is notably susceptible to honey fungus[].
The bruised leaves have a pleasant sweet though resinous smell[].

Edible Uses

Seed - eaten raw or used in confections, cakes, ice cream etc[, , , , ]. A delicious flavour. The seed can also be ground into a meal and used as a flavouring in sweet and savoury dishes[]. Whole walnuts and walnut products (such as walnut flour) are of high popularity as a health food as they contain an antioxidants and antimutagenics and as a super food due to high protein content[].
The unripe fruits are pickled in vinegar[].

An edible oil is obtained from the seed[, , , ], it should not be stored for any length of time since it tends to go rancid quickly[, ]. The oil has a pleasant flavour and is used in salads or for cooking[].

The sap is tapped in spring and used to make a sugar[].

The finely ground shells are used in the stuffing of 'agnolotti' pasta[]. They have also been used as adulterant of spices[].

The dried green husks contain 2.5 - 5% ascorbic acid (vitamin C) - this can be extracted and used as a vitamin supplement[].

The leaves are used as a tea[].

Medicinal

The walnut tree has a long history of medicinal use, being used in folk medicine to treat a wide range of complaints. Virtually all parts of the plant are used, different parts being considered to have their own unique properties and applications[, ].

The leaves are alterative, anthelmintic, antiseptic, anti-inflammatory, antispasmodic, astringent and depurative[, , ]. They are used internally the treatment of constipation, chronic coughs, asthma, diarrhoea, dyspepsia etc[]. The leaves are also used to treat skin ailments and purify the blood[, ]. They are considered to be specific in the treatment of strumous sores[].

Male inflorescences are made into a broth and used in the treatment of coughs and vertigo[].

The rind is anodyne and astringent[]. It is used in the treatment of diarrhoea and anaemia[].

The seeds are antilithic, diuretic and stimulant[]. They are used internally in the treatment of low back pain, frequent urination, weakness of both legs, chronic cough, asthma, constipation due to dryness or anaemia and stones in the urinary tract[].
Externally, they are made into a paste and applied as a poultice to areas of dermatitis and eczema[].

The oil from the seed is anthelmintic[]. It is also used in the treatment of menstrual problems and dry skin conditions[].

The cotyledons are used in the treatment of cancer[]. Walnut has a long history of folk use in the treatment of cancer, some extracts from the plant have shown anticancer activity[].

The bark and root bark are anthelmintic, astringent and detergent[, ].

The roots are antiseptic[]. The dried roots are rubbed on teeth to make the lips and gums red, healthy and strong[].

The plant is used in Bach flower remedies - the keywords for prescribing it are 'Oversensitive to ideas and influences' and 'The link-breaker'[].

Other Uses

A yellow dye is obtained from the green husks[, , , ]. It is green[]. The green nuts (is this the same as the green husks?) and the leaves are also used[]. The rind of unripe fruits is a good source of tannin[].
A brown dye is obtained from the leaves and mature husks[, , , , ]. It does not require a mordant and turns black if prepared in an iron pot[]. The dye is often used as a colouring and tonic for dark hair[]. The leaves and the husks can be dried for later use[].
A golden-brown dye is obtained from the catkins in early summer. It does not require a mordant[].

A drying oil is obtained from the seed. It is used in soap making, paints, etc. It is not very stable and quickly goes rancid[, , , ].

The nuts can be used as a wood polish. Simply crack open the shell and rub the kernel into the wood to release the oils. Wipe off with a clean cloth[, , ].

The dried fruit rind is used to paint doors, window frames etc[] (it probably protects the wood due to its tannin content).

The shells may be used as anti-skid agents for tyres, blasting grit, and in the preparation of activated carbon[].

An extract of the wood is used as an ingredient in commercial cosmetic preparations as a skin conditioner[].
The shell is used as an ingredient in commercial cosmetic preparations as an abrasive, skin conditioner[].
The seed and oil are used as ingredients in commercial cosmetic preparations as emollients and skin conditioners[].
An extract of the leaves is used as an ingredient in commercial cosmetic preparations as an abrasive, astringent, bulking agent, cleanser, masking agent and skin conditione[].
An extract of the flowers is used as an ingredient in commercial cosmetic preparations as a skin conditioner[].

The leaves contain juglone, this has been shown to have pesticidal and herbicidal properties[]. The crushed leaves are an insect repellent[, ].
Juglone is also secreted from the roots of the tree, it has an inhibitory effect on the growth of many other plants[].

Bark of the tree and the fruit rind are dried and used as a tooth cleaner. They can also be used fresh[, ].

Wood - heavy, hard, durable, close grained, seasons and polishes well. A very valuable timber tree, it is used for furniture making, craft pieces, 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[, , ].
Named varieties are propagated by budding.