and
Turkish cuisine. The two most commercially important species are
J. regia for timber and nuts, and
J. nigra for timber. Both species have similar cultivation requirements and are widely grown in temperate zones. Walnuts are light-demanding species that benefit from protection from wind. Walnuts are also very hardy against drought. Interplanting walnut plantations with a
nitrogen fixing plant, such as
Elaeagnus × ebbingei or
Elaeagnus umbellata, and various
Alnus species, results in a 30% increase in tree height and girth (Hemery 2001). When grown for nuts, care must be taken to select
cultivars that are compatible for pollination purposes; although some cultivars are marketed as "self fertile", they will generally fruit better with a different pollination partner. Many different cultivars are available for growers, and offer different growth habits, flowering and leafing, kernel flavours and shell thicknesses. A key trait for more northerly latitudes of North America and Europe is
phenology, with ‘late flushing’ being particularly important to avoid frost damage in spring. Some cultivars have been developed for novel ‘hedge’ production systems developed in Europe and would not suit more traditional orchard systems.
Flowers The leaves and blossoms of the walnut tree normally appear in spring. The male cylindrical catkins are developed from leafless shoots from the past year; they are about in length and have a large number of little flowers. Female flowers appear in a cluster at the peak of the current year’s leafy shoots.
Fruit The fruits of the walnut are a type of
accessory fruit known as a pseudodrupe (or drupe-like nut), the outer covering of the fruit is an
involucre – in a drupe the covering would be derived from the carpel.
Nuts and kernels The nut kernels of all the species are edible, but the walnuts most commonly traded are from the
J. regia, the only species which has a large nut and thin shell.
J. nigra kernels are also produced commercially in the US. Two-thirds of the world export market and 99% of US walnuts are grown in California's
Central Valley and in Coastal Valleys, from
Redding in the north to
Bakersfield in the south. Of the more than 30 varieties of
J. regia grown there, Chandler and Hartley account for over half of total production. In some countries, immature nuts in their husks are preserved in
vinegar. In the UK, these are called
pickled walnuts and this is one of the major uses for fresh nuts from the small scale plantings. In
Armenian cuisine, unripe walnuts, including husks, are preserved in sugar syrup and eaten whole. In Italy,
liqueurs called
Nocino and
Nocello are flavoured with walnuts, while
Salsa di Noci (walnut sauce) is a pasta sauce originating from
Liguria. In
Georgia, walnuts are ground with other ingredients to make
walnut sauce. . Walnuts are heavily used in India. In
Jammu, they are used widely as a
prasad (offering) to Mother Goddess Vaisnav
Devi and, generally, as a dry food in the season of festivals such as
Diwali. The nuts are rich in
oil, and are widely eaten both fresh and in
cookery. Walnut oil is expensive and consequently is used sparingly; most often in
salad dressings. Walnut oil has been used in
oil paint, as an effective binding medium, known for its clear, glossy consistency and nontoxicity. Manos and Stone studied the composition of seed oils from several species of the
Rhoipteleaceae and
Juglandaceae and found the nut oils were generally more unsaturated from species which grow in the
temperate zones and more saturated for species which grow in the
tropical zones. In the northerly-growing section
Trachycaryon,
J. cinerea oil was reported to contain 15%
linolenate (the report did not specify whether the linolenate was the alpha (n-3) or gamma (n-6) isomer, or perhaps a mixture), 2% of saturated
palmitate, and a maximum concentration of 71%
linoleate. In the section
Juglans,
J. regia nut oil was found to contain from 10% to 11% linolenate, 6% to 7% palmitate, and a maximum concentration of linoleate (62% to 68%). In the section
Cardiocaryon, the nut oils of
J. ailantifolia and
J. mandshurica were reported to contain (respectively) 7% and 5% of linolenate, 2% of palmitate, and maximum concentrations of 74% and 79% linoleate. Within the section
Rhysocaryon, the nut oils of the U.S. native black walnuts
J. microcarpa and
J. nigra were reported to contain (respectively) 7% and 3% linolenate, 4% and 3% palmitate, and 70% and 69% linoleate. The remaining results for black walnuts were:
J. australis contained 2% linolenate, 7% palmitate, and 61% linoleate;
J. boliviana contained 4% linolenate, 4% palmitate, and 70% linoleate;
J. hirsuta contained 2% linolenate, 5% palmitate, and 75% linoleate;
J. mollis contained 0% linolenate, 5% palmitate, 46% linoleate, and 49%
oleate;
J. neotropica contained 3% linolenate, 5% palmitate, and 50% linoleate; and
J. olanchana contained only a trace of linolenate, 9% palmitate, and 73% linoleate;
Shells The walnut shell has a wide variety of uses. Eastern black walnut (
J. nigra) shell is the hardest of the walnut shells, and therefore has the highest resistance to breakdown. ;Cleansing and polishing :Walnut shells are mostly used to clean soft metals, fiberglass, plastics, wood and stone. This environmentally friendly and recyclable soft grit abrasive is well suited for air blasting, deburring, descaling, and polishing operations because of its elasticity and resilience. Uses include cleaning automobile and jet engines, electronic circuit boards, and paint and graffiti removal. For example: In the early days of jet transportation, crushed walnut shells were used to scour the compressor airfoils clean, but when engines with air cooled vanes and blades in the turbine started being manufactured, this practice was stopped because the crushed shells tended to plug up the cooling passages to the turbine, resulting in turbine failures due to overheating. ;Oil well drilling : The shell is used widely in oil well drilling for lost circulation material in making and maintaining seals in fracture zones and unconsolidated formations. ;Flour : Flour from walnut shells can be used in thermoplastic starch composites to substitute oil derivatives. ;Paint thickener : Walnut shells are added to paint to give it a thicker consistency for "plaster effect" ranges. ;Explosives : Used as a filler in dynamite. ;Cosmetic cleaner : Occasionally used in soap and exfoliating cleansers.
Husks s Walnut husks are often used to create a rich yellow-brown to dark brown
dye used for dyeing
fabric, yarn or
wood and for other purposes. The dye does not require a
mordant and will readily stain the hand if picked without gloves.
Wood , scale in mm The common walnut, and the black walnut and its allies, are important for their attractive timber, which is hard, dense, tight-grained and polishes to a very smooth finish. The color is dark chocolate or similar in the heartwood changing by a sharp boundary to creamy white in the sapwood. When kiln-dried, walnut wood tends toward a dull brown color, but when air-dried can become a rich purplish-brown. Because of its color, hardness and grain, it is a prized furniture and carving wood. When walnut
vascular cambium is involved in a crotch (a branch fork), it behaves unusually, producing characteristic "crotch figure" in the wood which it makes. The grain figure exposed when a crotch in a walnut log is cut in the plane of its one entering branch and two exiting branches is attractive and sought after. There are some differences between the wood of the European walnut (
Juglans regia) and the wood of the black walnut (
Juglans nigra). For example,
Juglans regia wood sometimes has patches with a wavy texture. Black walnut wood tends to be darker than European walnut wood, and can suffer from paler sapwood that only really comes to light when the wood has been planed. Walnut wood has been the timber of choice for gun makers for centuries, including the
Gewehr 98 and
Lee–Enfield rifles of the First World War. It remains one of the most popular choices for rifle and shotgun stocks, and is generally considered to be the premium – as well as the most traditional – wood for gun stocks, due to its resilience to compression along the grain. Walnut is also used in
lutherie and for the body of
pipe organs. Walnut
burls (or "burrs" in the rest of the world) are commonly used to create bowls and other turned pieces. Walnut burl
veneer is one of the most valuable and highly prized by cabinet makers and prestige car manufacturers. The wood of the
butternut and related Asian species is of much lower value, softer, coarser, less strong and heavy, and paler in colour. Freshly sawn walnut heartwood may be greenish in color, but with exposure to air this color quickly changes to brown due to oxidation of the pigment. In North America, forestry research has been undertaken, mostly on
J. nigra, aiming to improve the quality of planting stock and markets. In some areas of the US, black walnut is the most valuable commercial timber species. The Walnut Council is the key body linking growers with scientists. In Europe, various EU-led scientific programmes have studied walnut growing for timber. The
Cherokee Indians would produce a black dye from walnut bark, which they used to dye cloth. As early as the 2nd century CE, shells and kernels of the edible walnut were used to make a dye solution in the
Levant.
Parkland and garden trees Walnuts are very attractive trees in parks and large gardens. Walnut trees are easily propagated from the nuts. Seedlings grow rapidly on good soils. However, different walnut species vary in the amount of juglone they release from the roots and fallen leaves –
J. nigra, in particular, is known for its toxicity, both to plants and horses. Juglone is
toxic to plants such as tomato, apple, and
birch, and may cause stunting and death of nearby vegetation. Juglone appears to be one of the walnut's primary defence mechanisms against potential competitors for resources (water, nutrients and sunlight), and its effects are felt most strongly inside the tree's "drip line" (the circle around the tree marked by the horizontal distance of its outermost branches). However, even plants at a seemingly great distance outside the drip line can be affected, and juglone can linger in the soil for several years even after a walnut is removed as its roots slowly decompose and release juglone into the soil.
Walnut as wildlife food plants Walnut species are used as food plants by the
larvae of some
Lepidoptera species. These include: •
Brown-tail moth (
Euproctis chrysorrhoea) •
Coleophora case-bearers (moths)
C. laticornella (recorded on
J. nigra) and
C. pruniella. •
Common emerald (a geometer moth) (
Hemithea aestivaria) •
Small emperor moth (
Pavonia pavonia) •
The engrailed (a geometer moth) (
Ectropis crepuscularia) •
Walnut sphinx moth (
Amorpha juglandis) •
The bride (a moth) (
Catocala neogama) –
nominate subspecies on butternut and others,
C. n. euphemia on Arizona black walnut, perhaps Texas black walnut and others. The nuts are consumed by other animals, such as mice and squirrels. In California (US) and Switzerland, crows have been witnessed taking walnuts into their beaks, flying up to 60 feet or so in the air, and dropping them to the ground to crack the shells and eat the nut inside. ==Nutritional information==