Juglans nigra L.
Eastern black walnut
Source: James A. Duke. 1983. Handbook of Energy Crops. unpublished.
- Folk Medicine
- Yields and Economics
- Biotic Factors
- Chemical Analysis of Biomass Fuels
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
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
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, 1.32 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 57.5
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, 3060 cm long, petioles
pubescent, with 1323 leaflets; leaflets 7.58 cm long, 2.53 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, 7.512.5 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 2030,
in many series, connectives purple, truncate, nearly sessile; pistillate aments
in 25-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, 35 cm in diameter, indehiscent; nut oval, oblong or round,
rough or sculptured, 33.5 cm in diameter, dark brown tinged red, 4-celled at
base, slightly 2-celled at apex; kernel sweet, soon becoming rancid. 2n
= 32. Fl. AprilMay; 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 4.98.2 (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 23-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, 140180 days; south to North Carolina, northern Georgia,
Alabama, Mississippi, Arkansas and Oklahoma, 180200 days; south of that,
220260 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 23 weeks; nuts can then be stored in cool, dry place until needed. Nuts
are cracked and kernels removed for use.
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 1530 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 56
years, these three varieties bear about one-forth bushel of nuts; at 1520
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.
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).
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
- Duke, J.A. 1978. The quest for tolerant germplasm. p. 161. In: ASA Special
Symposium 32, Crop tolerance to suboptimal land conditions. Am. Soc. Agron.
- Duke, J.A. 1979. Ecosystematic data on economic plants. Quart. J. Crude Drug
- Jenkins, B.M. and Ebeling, J.M. 1985. Thermochemical properties of biomass
fuels. Calif. Agric. 39(5/6):1416.
- Reed, C.F. 1976. Information summaries on 1000 economic plants. Typescripts
submitted to the USDA.
Last update Wednesday, January 7, 1998 by aw