Index | Search | Home

new crop logo

Juglans nigra L.

Eastern black walnut

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 unpublished.

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


Black walnut is one of most valuable natural forest trees in the United States. The nuts furnish a food product, used mainly for flavoring baked goods, pastries, and confectioneries. Wood has good texture, strength, and is coarse-grained, very durable, of a rich dark brown color with light sapwood; used in cabinet-making, gun-stocks, interior finishes of houses, furniture, airplanes, shipbuilding. Wood is also easy to work, resistant to destructive fungi and insect pests. Woody shells on fruits used to make jewelry. Green fruit husks boiled to provide a yellow dye. Trees used for shade and ornamentals.

Folk Medicine

The bark and leaves are considered alterative, astringent, detergent, laxative, and purgative. They are used for eczema, herpes, indolent ulcers, scrofula. The unripe fruit is sudorific and vermifugal, and used for ague and quinsy, and is rubbed onto cracked palms and ringworm. Oil from the ripe seeds is used externally for gangrene, leprosy, and wounds. 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. Indians used the root bark as vermifuge. Macerated in warm water, the husks and/or leaves, are said to destroy insects and worms, without destroying the grass. Insects are said to avoid the walnut, hence it is often used as a poor man's insect repellent. Rubbed on cattle and horses faces, walnut leaves are said to repel flies. The roots and/or leaves exude substances which are known to inhibit germination and/or growth of many plant species. All parts of the plant contain juglone which inhibits other plant species. Juglone has antihemorrhagic activity.


The genus Juglans is reported to contain the following "toxins": folic acid, furfural, inositol, juglone, nicotine, and tryptophane. Juglone has an oral LD50 of 2500 mg in mice. Chloroform is reported to constitute 86% of the essential oil of the leaves [Hort. Abs. 04416(051)]. Per 100 g, black walnut contains 3.1% water, 628 calories, 20.5 g protein, 59.3 g fat, 14.8 g total carbohydrate (1.7 g fiber), 2.3 g ash, a trace of Ca, 570 mg P, 6 mg Fe, 3 mg Na, 460 mg K, 300 IU Vitamin A, 0.22 mg thiamine, 0.11 mg riboflavin and 0.7 mg niacin.


The pollen may induce hay fever.


Tree up to 33 m tall, occasionally to 50 m, and often 100 years old; trunk straight, often unbranched for 20 m, 1.3–2 m in diameter; branches forming a round-topped crown, mostly upright and rigid; branchlets covered at first with pale or rusty matted hairs, and raised conspicuous orange lenticels; bark 5–7.5 cm thick, dark brown tinged red, deeply furrowed with broad rounded ridges; twigs light brown with channeled pith; terminal bud as broad as long; no hairy fringe above leaf-scar; leaves compound, deciduous, 30–60 cm long, petioles pubescent, with 13–23 leaflets; leaflets 7.5–8 cm long, 2.5–3 cm wide, long-pointed, sharply serrate, slightly rounded at base, yellow-green, thin, glabrous above, soft-pubescent beneath, turning bright yellow in fall before falling; staminate aments thick, 7.5–12.5 cm long, compact, not-stalked, single; calyx 6-lobed, lobes concave, nearly orbicular, pubescent on outer surface, its bract nearly triangular with rusty brown tomentum; stamens 20–30, in many series, connectives purple, truncate, nearly sessile; pistillate aments in 2–5-flowered spikes, bracts with pale glandular hairs, green, puberulous, calyx-lobes ovate, acute, puberulent on outer surface, glabrous or pilose within; fruit solitary or in pairs, globose, oblong or pointed at apex; husk yellow-green or green, smooth or roughened with clusters of short pale articulate hairs, 3–5 cm in diameter, indehiscent; nut oval, oblong or round, rough or sculptured, 3–3.5 cm in diameter, dark brown tinged red, 4-celled at base, slightly 2-celled at apex; kernel sweet, soon becoming rancid. 2n = 32. Fl. April–May; fr. at frost in fall.


At present, nearly 100 cvs of black walnuts have been selected and named. Many can be propagated to order, or scions may be obtained for grafting upon established stocks. Cultivars differ in hardiness, response to length of growing season, summer heat, resistance to diseases and susceptibility to insect damage. 'Thomas' is the most cultivated variety in New York; 'Snyder' and 'Cornell' have good cracking quality for northern areas; 'Wiard', for Michigan; 'Huber' and 'Cochrane', for Minnesota; 'Sparrow', 'Stambaugh' and 'Elmer Myers' are all good in parts of South; 'Ohio' and 'Myers', good in north central areas. Natural hybrid, X Juglans intermedia Carr (J. nigra x J. regia) has been recorded in United States and Europe. In California, 'Royal' (J. nigra x J. hindsii) has been artificially produced (Reed, 1976). Reported from the North American Center of Diversity, walnut is reported to be relatively tolerant to disease, drought, fire, frost, fungi, high pH, heat, insects, limestone, slopes, smog, and weeds. (2n = 32) (Duke, 1978)


Grows naturally in 32 states and in southern Ontario, Canada, most abundant in Allegheny Mountains to North Carolina and Tennessee. Occasionally cultivated as ornamental in eastern United States, western and central Europe. Planted in Europe for timber.


Wind pollinated. Suited to rich bottomlands and fertile hillsides from lower Hudson Valley southward, walnut will grow a few hundred miles outside its natural range, but may not bear nuts. Seedling trees mature fruit rather generally throughout area with a growing season of about 150 days and an average summer temperature of 16.5°C. Best suited to deep, rich, slightly acid or neutral soil, with good drainage, but will not succeed on infertile upland soil or on soils with poor drainage. Reliable indicators for suitable land are good stand of white oak and tulip popular, or where corn grows well. Because trees have a deep taproot, they are drought resistant. Ranging from Cool Temperate Moist to Wet through Subtropical Moist Forest Life Zones, black walnut is reported from areas with annual precipitation from 3 to 13 dm (mean of 19 cases = 9), annual temperature from 7 to 19°C (mean of 19 cases = 11), and pH from 4.9–8.2 (mean of 15 cases 6.3). (Duke, 1978, 1979)


Improved varieties do not come true from seed; hence, propagated by grafting scions (twigs) from trees of desired varieties onto main stems of 2–3-year old native seedlings. Scions develop crowns that bear nuts of their own variety. As there is little information available to indicate the best cvs for different localities, local nurseries should be consulted. Trees are 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 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. Young plants are best transplanted in early spring, when new roots will grow rapidly to replace those lost in transplanting. In South, young trees may be planted in fall or winter. For nut production, trees spaced 20 m apart. For trees up to 2.3 m tall, dig hole 0.6 m deep and 1 m wide. Place tree at same depth in hole as it stood in nursery and spread out roots well. Fill hole with topsoil and firm down soil. Form a basin around edge of hole and soak soil immediately. Black walnuts require large quantities of nitrogen and phosphorus. Apply mixed fertilizer (5-10-5 or 10-10-10) each year under tree branches when buds begin to swell in early spring. Rates of 450 g/yr of 5-10-5 fertilizer, or 230 g/yr for 10-10-10, per tree. Do not use during first year, because of danger of injuring roots. In strongly acid soils, apply lime to change pH to 6 or 6.5. Do not over-lime, as this makes zinc in soil unavailable to tree. Soils east of Mississippi River are often deficient in magnesium. Crushed dolomite limestone is used to correct this condition and reduce acidity of soil. Prune any suckers that come from below graft on trunk. In orchards, trees over 15 years old may be interseeded with grasses and legumes and animals turned in to pasture, as they will not damage older trees. All black walnuts tend to bear heavy nut crops every second year. No cultural practices have been developed to offset this type of alternating. Some trees bear every year, while others bear every third year. Others mainly react to climatic conditions with no pattern. In United States growing seasons are divided into 3 zones: North of Mason-Dixon Line, 140–180 days; south to North Carolina, northern Georgia, Alabama, Mississippi, Arkansas and Oklahoma, 180–200 days; south of that, 220–260 days. Varieties are selected for each area. When trees bearing fruits of exceptional quality are found, they are propagated and cultivated for nut production in that area.


Nuts are havested from native trees as well as from improved selections and cultivars. Fruit ripens in one season, usually by late September or early October. Most production is from wild trees growing on non-crop land, and these represent the main commerical source of kernels for today's market. Nuts should be harvested as soon as they fall, in order to get light-colored kernels with mild flavor. Leaving them on ground causes some discoloration of kernel. Hulls of native trees are thick and heavy, whereas those of 'Thomas' and 'Ohio' have thinner hull, those of 'Myers' being thinnest of all. Hull may be mashed and removed by hand, or by mechanical devices. After removing the hulls, nuts should be washed thoroughly and spread out to dry in direct sunlight. Drying takes 2–3 weeks; nuts can then be stored in cool, dry place until needed. Nuts are cracked and kernels removed for use.

Yields and Economics

Although Duke (1978) reported yields of 7.5 MT seeds, this is probably highly optimistic. Elsewhere it is said that 95% of the wild black walnut seeds are empty or aborted. Perhaps yields could be as high as 2.5 MT/ha under intensive management, which is attainable in the commercial walnut, Juglans regia. Selections are made based on weight of nuts. Trees may bear at rates of 7,500 seed/ha. Nuts from wild trees weigh about 17 g (27 nuts per lb); for selected varieties, weights vary from 15–30 g; those 20 g or over are: 'Michigan' (20); 'Grundy', 'Monterey', 'Schreiber' and 'Thomas' (21); 'Victoria' (22); 'Hare' (23); 'Pinecrest' (25); and 'Vandersloot' (30). 'Thomas', 'Ohio' and 'Myers' begin bearing nuts in second or third year after planting, while native trees usually do not begin to bear until about 10 years after planting. In 5–6 years, these three varieties bear about one-forth bushel of nuts; at 15–20 years of age, the first two bear 2 bu of nuts, 'Myers' about 1 bu, and native trees about one-fourth bu. Lumber trees yield about 1150 board feet at 76 years old. Nut shelling industry centered in and around Arkansas, Kansas, Kentucky, Missouri, Oklahoma, Tennessee, West Virginia and Virginia. Because of scarcity of trees and long growing period required to get wood, walnut lumber is not in great demand as it used to be. More frequently grown in Europe for lumber. Walnuts grown in United States for nuts and ornament. Well-formed trees will yield lumber worth thousands of dollars.


Oil contents of the seeds run about 60%, suggesting that if the walnut yields of 7.5 MT/ha were attained, there might be as much as 4.5 MT/oil there. Hulls and exocarp might be used to fuel the processing, as the value of the timber improves with age (one tree commanded $35,000 at an Ohio auction). Prunings and culls, as well as fallen and dead limbs might amount to 5 MT/ha/year.

Biotic Factors

Walnut anthracnose is most serious disease to native trees. 'Ohio' is resistant to this disease; 'Myers' is less resistant. Disease overwinters in fallen leaves and reinfects new leaflets in mid May until mid June, often defoliating entire trees. Many nuts are empty or contain blackened, shriveled kernels. Bunch disease, the cause and means of spread are unknown, stunts growth of tree and lowers nut production. Most serious insect pests are walnut lace bug, curculios, walnut husk maggot, walnut caterpillar and fall webworm. Serious damage may also be caused by leaf-eating caterpillars, scales, aphids and twig girdlers. County agricultural agents should be consulted for measures to control these in a particular area. Nematodes include Meloidogyne sp., Pratylenchus coffeae, P. pratensis, and P. vulnus (Golden, p.c. 1984).

Chemical Analysis of Biomass Fuels

Analysing 62 kinds of biomass for heating value, Jenkins and Ebeling (1985) reported a spread of 19.83 to 18.65MJ/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 80.69% volatiles, 0.78% ash, 18.53% fixed carbon, 49.80% C, 5.82% H, 43.25% O, 0.22% N, 0.01% S, 0.05% Cl, and undetermined residue.


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