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Juglans regia L.

English walnut, Carpathian or Persian walnut

Source: James A. Duke. 1983. Handbook of Energy Crops. unpublished.

  1. Uses
  2. Folk Medicine
  3. Chemistry
  4. Description
  5. Germplasm
  6. Distribution
  7. Ecology
  8. Cultivation
  9. Harvesting
  10. Yields and Economics
  11. Energy
  12. Biotic Factors
  13. Chemical Analysis of Biomass Fuels
  14. References


Principal value is an orchard tree for commercial production of nuts. Nuts consumed fresh, roasted, or salted, used in confectioneries, pastries, and for flavoring. The shells may be used as antiskid agents for tires, blasting grit, and in the preparation of activated carbon. (Activated charcoal and fructose have recently been suggested to foil the alcohol "breathalizer.") Ground nut shells used as adulterant of spices. Crushed leaves, or a decoction used as insect repellant and as a tea. Outer fleshy part of fruit very rich in Vitamin C and produces a yellow dye. Fruit, when dry pressed, yields a valuable oil used in paints and in soap-making; when cold pressed, a light yellow edible oil used in foods as flavoring. Young fruits made into pickles, also used as fish poison. Twigs and leaves lopped for fodder in India. Decoction of leaves, bark, and husks used with alum for staining wool brown. Wood hard, durable, close-grained, heavy, used for furniture and gun-stocks. Tree often grown as ornamental.

Folk Medicine

According to Hartwell (1967–1971), the English walnuts are used in folk remedies for aegilops, cancer, carbuncles, carcinoma, condylomata acuminata, corns, excrescences, growth, indurations, tumors, warts, and whitlows, especially cancerous conditions of the breast, epithelium, fauces, groin, gullet, intestine, kidneys, lip, liver, mammas, mouth, stomach, throat, and uterus. Reported to be alterative, anodyne, anthelmintic, astringent, bactericide, cholagogue, depurative, detergent, digestive, diuretic, hemostat, insecticidal, laxative, lithontryptic, stimulant, tonic, and vermifuge, the English walnut is a folk remedy for anthrax, asthma, backache, caligo, chancre, colic, conjunctivitis, cough, dysentery, eczema, ejaculation, favus, heartburn, impotence, inflammation, intellect, intestine, intoxication, kidney, legs, leucorrbea, lungs, rheumatism, scrofula, sore, syphilis, and worms (Duke and Wain, 1981).


Per 100 g, the seed is reported to contain 647–657 calories, 2.5–4.2 g H2O, 13.7–18.2 g protein, 63.6–67.2 g fat, 12.6–15.8 g total carbohydrate, 1.6–2.1 g fiber, 1.7–2.0 g ash, 92–106 mg Ca, 326–380 mg P, 3.0–3.3 mg Fe, 2–3 mg Na, 450–536 mg K, 0.50 mg b-carotene equivalent, 0.27–0.50 mg thiamine, 0.08–0.51 mg riboflavin, 0.7–3.0 mg niacin, and 0–5 mg ascorbic acid. Wealth of India (C.S.I.R. 1948–1976) also reports, per 100 g, 2.7 mg Na, 687 mg K, 61 mg Ca, 131 mg Mg, 2.4 mg Fe, 0.3 mg Cu, 510 mg P, 104 mg S, and 23 mg Cl, and 2.8 mg I (as well as Ar, Zn, Co, and Mn). About 42% of the total phosphorus is in phytic acid; lecithin is also present. The immature fruit is one of the richest sources of ascorbic acid, the skin with 1,090 mg, 100 g, the pulp with 2,330 mg. The leaves, also rich in ascorbic acid (almost 1% of the weight), are rich in carotene (ca 0.3% wet weight). Juglone is the active compound in the leaves; also quercetin, cyanadin, kaempferol, caffeic acid, and traces of p-coumaric acid, hyperin (0.2%), quercitrin, kaempferol-3-arabinoside, quercetin-3-arabinoside. The seed oil contains 3–7% palmitic, 0.5–3% stearic, 9–30% oleic, 57–76% linoleic, and 2–16% linolenic acids. The oil cake, with 86.6% dry matter, contains 35.0% protein, 12.2% fatty oil, 27.6% carbohydrates, 6.7% fiber, 5.1% ash (Digestible nutrients: 31.5% crude protein, 11.6% fatty oil, 23.5% carbohydrates, and 1.7% fiber). The shells contain 92.3% DM, 1.7% protein, 0.7% fatty oil, 31.9% carbohydrates, 56.6% fiber, and 1.4% ash.


Deciduous, monoecious trees, 12–15 m tall (Payne vars.), 17–20 m tall (Eureka, Placentia, Mayette, Franquette), and rarely up to 60 m tall; bark brown or gray, smooth, fissured; leaf-scars without prominent pubescent band on upper edge; leaves alternate, foetid, pinnate, without stipules; leaflets to ovate-lanceolate, acuminate; margin irregularly serrate, glabrescent above, pubescent and glandular beneath; flowers developing from dormant bud of previous season's growth; staminate flowers in axillary, pendulous aments 5–15 cm long, developing 1–4 million pollen grains each; flowers in axils of scales, with 2 bracteoles, perianth-segments 1–4, stamens 3–40; pistillate flowers in clusters of 3–9, developing as many nuts; in selected varieties not only terminal bud produces fruit, but all lateral buds on previous years growth also produce; perianth 4-lobed; fruit 3.5–5 cm in diameter, globose or slightly ridged, not splitting.


Reported from the Eurosiberian and Central Asian Centers of Diversity, English walnut, or cvs thereof, is reported to tolerate frost, high pH, heat, insects, low pH, and slope (Duke, 1978). Cultivars are selected on basis of high heat tolerance, resistance to walnut blight (Xanthomonas juglandis), tolerance for winter cold, and yield and quality of kernels. Most promising cvs are of Carpathian origin and have been introduced from Poland and withstand temperatures below those recorded in the fruit belt of New York. Recent superior cvs include: 'Broadview', 'Schafer', 'Littlepage', 'McKinster', 'Metcalfe', 'Jacobs', and 'Colby'. Other cvs widely grown in the world include: 'Marmot', 'Meylanaise', 'Corne', 'Gourlande', 'Mayette', 'Brantome', 'Ashley', 'Glackner', 'Nugget', 'Poe', 'Franquette', 'Concord', 'Ehrhardt', 'Payne', and 'Waterloo'. Persian walnuts have been hybridized with butternuts, black walnuts, and other European and Oriental walnuts. Juglans regia var. orientis (Dode) Kitam. J. orientis Dode; J. regia var. sinensis sensu auct. (Japan, non DC.) is a widely cultivated Chinese tree, with glabrous leaves and branchlets, leaflets 3–9, obtuse, entire, except in young trees, and nuts relatively thin-shelled. (2n = 32, 36)


Native to the Carpathian Mountains of eastern Europe, but often found growing wild eastward to Himalayas and China. Widely cultivated throughout this region and elsewhere in temperate zone of the Old and New World. Thrives in temperate Himalayas from 1,000 to 3,000 m altitude. In North America, thrives as far north as New York State. Introduced from Spain by way of Chile to California about 1867. In 1873 'Kaghazi' was introduced in northern California and a seedling 'Eureka' has become the important source of our commercial varieties.


Ranging from Cool Temperate Steppe to Wet through Subtropical Thorn to Moist Forest Life Zones, English walnut is reported to tolerate annual precipitation of 3.1 to 14.7 dm (mean of 25 cases = 8.4), annual temperature of 7.0 to 21.1°C (mean of 25 cases = 12.0), and pH of 4.5 to 8.2 (mean of 21 cases = 6.4). Thrives on rich, sandy loam, well-drained, slightly acid or neutral. Responds well to cultivation and fertilization. In areas where hardiness is a problem, trees should not be forced into excessive vegetative growth. Minimum temperature should not go below -29°C. One fault of Carpathian walnuts is that it begins growth early in spring with result that crop and foliage may be damaged by late frosts. When fully dormant, trees can withstand temperatures from -24°C to -27°C without serious damage. French cvs are more winter hardy. 'Eureka' is less hardy than newer cvs being produced for northern California, Oregon, and higher altitudes. Very high summer temperatures cause damage to kernels, slightly at 38°C, severe at 40.5 to 43.5°C. Quite variable resistance to heat among varieties. Reported from areas with pH 4.5 to 8.3 annual rainfall 03 to 15 dm and annual temperature 7–19°C. Rains in late spring and summer increase walnut blight infections.


Various methods are used for preparing an area for a walnut orchard, all giving equally good results, when measured by profitable crop production. Since trees are deep-rooted, soil should be fertile, well-drained, alluvial, 2 m or more deep, of medium loam to sandy or silt loam texture, and free of alkali salts, especially excessive boron. Seedling trees show great variation as to hardiness, type of fruit and fruitfulness. 'Paradox' hybrids, 'Royal' hybrids and Juglans hindsii are used as rootstocks for grafting Persian and Carpathian walnuts. Rootstock of Juglans regia may be used if oak root fungus (Armillaria mellea) is absent in area. Persian walnuts have been grafted to Chinese wingnut (Pterocarya stenoptera). Selected varieties are best whip or bark grafted or patch budded on seedling trees, or top-worked on existing trees. Persian walnuts are planted in the orchard from 10 to 20 m each way; however, many spacings are in use depending on the variety and the cultivation methods to be used. Intercropping young walnut orchard with trees of a different species may be useful, at least for the first 5–10 years. Intercropping may be difficult because of irrigation, spraying, and use of equipment for cultivation of the intercrop. Holes should be dug amply wide to accomodate roots, a few m deeper than the roots, and planted no deeper than they were in the nursery. Roots should never be allowed to dry out during the transplanting process. Topsoil should be used to fill hole when planting tree, and firmly tamped around roots. Do not transplant when soil is wet. Nut trees must have tops reduced or cut back, either before or after planting, usually to about 1.5–2 m from ground level. Lower buds should be suppressed so the upper ones will be forced to grow and make the framework of the tree. Newly planted trees should be staked, either with a single stake driven close to the tree and tying it to the stake, or driving three stakes equidistant, fastening tree to each with stout cord so as not to injure bark. After trees are planted, they should be watched, and watered during every severe dry spell until they have become established. When irrigated, total of 2 1/2–5 acre feet of water per acre should be applied through-out the year, including normal rainfall. The modified central leader system of training young walnuts is recommended for western orchards, in which 4 or 5 main framework branches spaced both vertically and horizontally are developed; the first branch should be started no lower than 2 m from the ground. Trend is toward heavier and more consistent pruning both in young and old trees; very fruitful new cvs respond more readily than some of the older cvs. Nitrogen and zinc deficiencies in soils are based on minimum of 100–150 kg/ha per year for bearing walnuts; 200 to 250 kg/ha are used on high-producing orchards. Standard method for applying zinc to walnut trees is to drive zinc-bearing metal pieces or glazing points into outer sapwood of trees. Other elements which may show mineral deficiencies in various soils and hence must be corrected are iron, manganese, boron, potassium, magnesium, phosphorus, and copper.


Under favorable conditions, the husks of nuts crack open and adhere temporarily to twigs, allowing nuts to fall to ground, this occurring with most cvs between September 1 and November 7. First picking up of nuts begins in second week of September. Hastening of falling of nuts is usually done by shaking the trees with long poles or a boom shaker. During harvest period, nuts are picked up 3 or 4 times before total crop has matured and dropped. Nuts should not be allowed to remain on ground too long. After being picked up and sacked, nuts are washed if dirty, and spread out in shallow trays with bottom slats spaced 1.5–2 cm apart. Nuts should not be exposed to sun for entire day. Trays are piled up so as to permit ventilation after nuts have become warm. Too fast drying causes shell to crack and open. In large orchards, a drying house is constructed for curing process. After curing and bleaching, nuts are graded and packed for shipment.

Yields and Economics

Newer cvs 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 MT/ha; orchards in well cultivated valleys, 6.5–7.5 MT/ha. According to the Wealth of India, a grown individual can yield about 185 kg, but 37 kg is more likely. In the United States, California is the major producing area, with about 129,400 acres producing 77,000 tons nuts per year; Oregon is second with about 3,500 tons annually; the total valued at about $32.3 million. About 60% of Persian walnuts are sold shelled. Lumber from large trees may bring up to $1,500/tree.


If the walnuts yields of 7,500 kg/ha (Duke, 1978) yielded all their 65% (63–67% oil) oil, there is a potential oil yield of nearly 5 MT per year, a very worthwhile target, if attainable. The green hulls have recoverable ascorbic acid (content 2.5–5% of dry weight). Hulls contain 12.2%, bark 7.5%, leaf blades 9–11% tannin. After extraction of the vitamin C and tannin, the residues might be used for fuel or ethanol. Prunings from the trees might contribute another 5 MT biomass per year.

Biotic Factors

Pollination is often a problem, as Persian walnuts are monoecious, with separate staminate and pistillate flowers in different parts of the same tree. Staminate catkins are 10–15 cm long and produce 1–4 million pollen grains each. Sometimes freshly picked catkins are put on paper in room at 21°C and the shed pollen stored in desiccator at 0°C. Then pollen is blown on trees by fan mounted on truck. Helicopters are sometimes used to blow pollen over orchard. Seedlings are very susceptible to mushroom root rot, and Walnut girdle disease 'Blackline' is thought to occur when certain horticulture varieties of Juglans regia are grafted on rootstocks of Juglans hindsii and its hybrids, associated with graft incompatibility. Fungi known to attack Persian walnuts include: Alternaria nucis, Armillaria mellea, Ascochyta juglandis, Aspergillus flavus, Auricularia auricula-judae, Auricularia mesenterica, Cerrena unicolor, Cladosporium herbarum, Coniophora cerebella, Coprinus micaceus, Coriolus tephroleucus, Cribaria violaceae, Cryptovalsa extorris, Cylindrosporium juglandis, C. juglandis, C. uljanishchevii, Cytospora juglandina, Cytosporina juglandina, C. juglandicola, Diplodia juglandis, Dothiorella gregaria, Erysiphe polygoni, Eutypa ludibunda, Exosporina fawcetti, Fomes fomentarius, F. igniarius, F. ulmarius, Fusarium avenaceum, F. lateritium, Ganoderma applanatum, Glomerella cingulata, Gnomonia ceratostyla, G. juglandis, G. leptostyla., Hemitricia leiotyichia, Hypoxylon mediterraneum, Inonotus hispidus, Laetiporus sulphureus, Lentinus cyathiformis, Licea tenera, Marsonia juglandis, Melanconis carthusiana, M. juglandis, Melanconium juglandis, M. oblongum, Melanopus squamosus, Microsphaera alni, M. juglandis, Microstroma juglandis, Mycosphaerella saccardoana, M. woronowi, Nectria applanata, N. cinnabarina, N. ditissima, Oxyporus populinus, Phellinus cryptarum, Phleospora multimaculans, Phoma juglandis, Phomopsis juglandis, Phyllactinia guttata, Phyllosticta juglandina, P. juglandis, Phymatotrichum omnivorum, Phytophthora cactorum, P. cinnamomi, P. citrophthora, Pleospora vulgaris, Pleurotus ostreatus, Polyporus hispidus, P. picipes, P. squamosus, Polystictus versicolor, Rhizopus nigricans, Stereum hirsutum, Trametes suaveolens, Tubercularia juglandis, T. vulgaris, Verticillium albo-atrum. Bacteria attacking Persian walnut include: Agrobacterium tumefaciens, Bacillus mesentericus, Bacterium juglandis, Pseudomonas juglandis, Xanthomonas juglandis, Cuscuta pentagona, also parasitized the tree. The following nematodes have been isolated from Persian walnut: Cacopaurus pestis, Diplogaster striatus, Diplogaster coronata, Ditylenchus intermedius, Meloidogyne arenaria, M. javanica, M. sp., Pratylenchus coffeae, P. pratensis, P. vulnus, Rhabditis debilicauda, R. spiculigera, Tylolaimophorus rotundicauda. Among the insect pests of this walnut are the following: Walnut Blister mite (Eriophytes tristriatus), Walnut aphid (Chromaphis juglandicola), Italian pear scale (Diaspis iricola), Calico scale (Eulecanium cerasorum), Frosted scale (Parthenolecanium Pruinosum), Walnut scale (Quadraspidiotus juglansregiae), Codling moth (Cydia pomonella), Fruit tree leaf-roller (Archips argyrospila), Indian meal moth (Plodia interpunctella), Walnut caterpillar (Datana integerrima), Red-humped caterpillar (Schizura concinna), Walnut span worm (Phigalia plumigeraria), and Walnut husk fly (Rhagolestis completa).

Chemical Analysis of Biomass Fuels

Analysing 62 kinds of biomass for heating value, Jenkins and Ebeling (1985) reported a spread of 19.63 to 18.49 MJ/kg, compared to 13.76 for weathered rice straw to 23.28 MJ/kg for prune pits. On a % DM basis, the orchard prunings contained 80.82% volatiles, 1.08% ash, 18.10% fixed carbon, 49.72% C, 5.63% H, 43.14% O, 0.37% N, 0.01% S, 0.06% Cl , and undetermined residue.


Complete list of references for Duke, Handbook of Energy Crops
Last update Wednesday, January 7, 1998 by aw