Juglans nigra

"Black walnut" redirects here. For other uses, see Black walnut (disambiguation).
Eastern black walnut
Leaves and fruit
Scientific classification
Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Rosids
Order: Fagales
Family: Juglandaceae
Genus: Juglans
Species: J. nigra
Binomial name
Juglans nigra
L.
Natural range

Juglans nigra, the eastern black walnut, is a species of deciduous tree in the walnut family, Juglandaceae, native to eastern North America. It grows mostly in riparian zones, from southern Ontario, west to southeast South Dakota, south to Georgia, northern Florida and southwest to central Texas. Wild trees in the upper Ottawa Valley may be an isolated native population or may have derived from planted trees.

Black walnut is an important tree commercially, as the wood is a deep brown color and easily worked. The fruits, walnuts, are cultivated for their distinctive and desirable taste. Often, trees are grown for both lumber and walnuts simultaneously and many cultivars have been developed for improved quality nuts or wood. Black walnut is currently under pressure from the thousand cankers disease which is causing decline of walnuts in some areas. Black walnut is also allelopathic which means that it releases chemicals from roots and other tissues which harm other organisms and give the tree a competitive advantage, this is often undesirable as it can harm garden plants and grasses.

Description

The fruit production tends to occur irregularly with some years producing larger crops than others (see mast year). Fruiting may begin when the tree is 4–6 years old, however large crops take 20 years. Total lifespan of J. nigra is about 130 years. Black walnut does not leaf out until late spring when the soil has warmed and all frost danger is past. Like other trees of the order Fagales, such as oaks, hickories, chestnuts, and birches, it is monoecious, with wind-pollinated catkins. Male and female flowers are in separate spikes, and the female flowers typically appear before the male on a single tree (dichogamy). As a consequence, self-pollination is unlikely. However, individual trees usually are not self-sterile; if they are not pollinated by neighboring trees, they may set self-fertilized seeds.[4] For maximum seed germination, the seeds should be cold-moist stratified for 3–4 months, although the exact time depends on the seed source.[4] The seedlings emerge in April or May and typically grow 90 cm (35 in) their first year and even more in the 2nd year.[4] Black walnut often loses its leaves earlier than other deciduous trees growing in the same area after having a growing period of 115–135 days.[4]

Black walnut has a strong taproot which makes the seedlings resilient, but difficult to transplant.

Black walnut is more resistant to frost than the English or Persian walnut, but thrives best in the warmer regions of fertile, lowland soils with high water tables, although it will also grow in drier soils, but much more slowly.[2] Some soils preferred by black walnut include Alfisol and Entisol soil types.[4] Walnut grows best on sandy loam, loam, or silt loam type soils but will also grow well on silty clay loam soils. It prefers these soils due to the fact that these soils hold large quantities of water which the tree draws from during dry periods.[4]

Visually, black walnut is similar to the butternut (Juglans cinerea) in leaf shape, and the range also overlaps significantly. The fruits are quite different, and their presence makes an identification easy, as black walnut fruits are round and butternuts are more oval-oblong shaped. When a fruit is not available, two species can be differentiated based on the leaf scars, or the place where the leaf meets the stem: butternut has a leaf scar with a flat upper edge and with a velvety ridge above that flat part, but black walnut has an indented leaf scar with no hairy ridge.[5]

Ecology

Black walnut is primarily a pioneer species similar to red and silver maple and black cherry. Because of this, black walnut is a common weed tree found along roadsides, fields, and forest edges in the eastern US. It will grow in closed forests, but is classified as shade intolerant, this means it requires full sun for optimal growth and nut production .

The nuts are food for many rodents and make up to 10% of the diet of eastern fox squirrels.[6] The nuts are also eaten by species of birds. The leaves are browsed by white tailed deer,[6] although they are not a preferred food. Squirrels benefit this species by distributing and burying the seeds; if the seeds are not reclaimed by the squirrel, they will germinate and help disperse the species.

Where the range of the eastern black walnut overlaps that of the Texas black walnut (J. microcarpa), the two species sometimes interbreed, producing populations with characteristics intermediate between the two species.[7] J.nigra and J. cinerea often grow in the same range as well but they do not hybridize naturally.[4][6]

The tree's roots often form endomycorrhizal relationships with fungi in the genus Glomus. Some endomycorrhizal relations improve the plant's growth.[4]

Species often associated with J. nigra include yellow-poplar (Liriodendron tulipifera), white ash (Fraxinus americana), black cherry (Prunus serotina), basswood (Tilia americana), American beech (Fagus grandifolia), sugar maple (Acer saccharum), oaks (Quercus spp.), and hickories (Carya spp.). Near the western edge of its range, black walnut may be confined to floodplains, where it grows either with American elm (Ulmus americana), common hackberry (Celtis occidentalis), green ash (Fraxinus pennsylvanica), and boxelder (Acer negundo), or with basswood and red oak (Quercus rubra) on lower slopes and other favorable sites.[4]

Uses

Walnut, black (J. nigra)

Black walnut
Nutritional value per 100 grams
Energy 2,586 kJ (618 kcal)
9.91 g
Starch 0.24 g
Sugars 1.10 g
Dietary fiber 6.8 g
59.00 g
Saturated 3.368 g
Monounsaturated 15.004 g
Polyunsaturated

35.077 g

2.006 g
33.072 g
24.06 g
Vitamins
Vitamin A equiv.
(0%)

2 μg

Vitamin A 40 IU
Thiamine (B1)
(5%)

0.057 mg

Riboflavin (B2)
(11%)

0.130 mg

Niacin (B3)
(3%)

0.470 mg

Pantothenic acid (B5)
(33%)

1.660 mg

Vitamin B6
(45%)

0.583 mg

Folate (B9)
(8%)

31 μg

Vitamin B12
(0%)

0 μg

Vitamin C
(2%)

1.7 mg

Vitamin D
(0%)

0 μg

Vitamin D
(0%)

0 IU

Vitamin E
(12%)

1.80 mg

Vitamin K
(3%)

2.7 μg

Minerals
Calcium
(6%)

61 mg

Iron
(24%)

3.12 mg

Magnesium
(57%)

201 mg

Manganese
(186%)

3.896 mg

Phosphorus
(73%)

513 mg

Potassium
(11%)

523 mg

Sodium
(0%)

2 mg

Zinc
(35%)

3.37 mg

Other constituents
Water 4.56 g
Percentages are roughly approximated using US recommendations for adults.
Source: USDA Nutrient Database

Planting

While its primary native region is the Midwest and east-central United States, the black walnut was introduced into Europe in 1629 and is also cultivated in Hawaii.[6] It is cultivated there and in North America as a forest tree for its high-quality wood. Black walnut plantings can be made to produce timber, nuts, or both timber and nuts. Patented timber-type trees were selected and released from Purdue University in the early 1990s. These trees have been sporadically available from nurseries. Varieties include Purdue #1, which can be used for both timber and nut production, though nut quality is poor compared to varieties selected specifically as nut producers.

Autumn foliage

Grafted, nut-producing trees are available from several nurseries operating in the U.S. Selections worth considering include Thomas, Neel #1, Thomas Myers, Pounds #2, Stoker, Surprise, Emma K, Sparrow, S127, and McGinnis. Several older varieties, such as Kwik Krop, are still in cultivation; while they make decent nuts, they would not be recommended for commercial planting. A variety index and characteristics guide is available from Missouri Extension.

Pollination requirements should be considered when planting black walnuts. As is typical of many species in Juglandaceae, Juglans nigra trees tend to be dichogamous, i.e.. produce pollen first and then pistillate flowers or else produce pistillate flowers and then pollen. An early pollen-producer should be grouped with other varieties that produce pistillate flowers so all varieties benefit from overlap. Cranz, Thomas, and Neel #1 make a good pollination trio. A similar group for more northern climates would be Sparrow, S127, and Mintle.

Sometimes black walnut is planted as part of reclaiming mines.[6] When growing young trees weed control is critical for healthy establishment of the trees, without weed control the young trees are harmed significantly in their growth rate.

J. nigra is also grown as a specimen ornamental tree in parks and large gardens, growing to 30 m (98 ft) tall by 20 m (66 ft) broad.[8] It has gained the Royal Horticultural Society's Award of Garden Merit.[9]

Food

Black walnut nuts are shelled commercially in the United States. About 65% of the annual wild harvest comes from the U.S. state of Missouri, and the largest processing plant is operated by Hammons Products in Stockton, Missouri. The nutmeats provide a robust, distinctive, natural flavor and crunch as a food ingredient. Popular uses include ice cream, bakery goods and confections. Consumers include black walnuts in traditional treats, such as cakes, cookies, fudge, and pies, during the fall holiday season. The nuts' nutritional profile leads to uses in other foods, such as salads, fish, pork, chicken, vegetables and pasta dishes.

Nutritionally similar to the milder-tasting English walnut, the black walnut kernel is high in unsaturated fat and protein. An analysis of nut oil from five named J. nigra cultivars (Ogden, Sparrow, Baugh, Carter and Thomas) showed the most prevalent fatty acid in J. nigra oil is linoleic acid (27.80–33.34 g/100g dry kernel), followed (in the same units) by oleic acid (14.52–24.40), linolenic acid (1.61–3.23), palmitic acid (1.61–2.15), and stearic acid (1.07–1.69).[10] The oil from the cultivar Carter had the highest mol percentage of linoleate (61.6), linolenate (5.97%), and palmitate (3.98%); the oil from the cultivar Baugh had the highest mol percentage of oleate (42.7%); the oil from the cultivar Ogden has the highest mol percentage of stearate (2.98%).

Tapped in spring, the tree yields a sweet sap that can be drunk or concentrated into syrup or sugar which is not unlike the sap of sugar maple.

Nut processing by hand

Hands after removing the husks from 500 black walnuts

The extraction of the kernel from the fruit of the black walnut is difficult. The thick, hard shell is tightly bound by tall ridges to a thick husk. The husk is best removed when green, as the nuts taste better if it is removed then. Rolling the nut underfoot on a hard surface such as a driveway is a common method; commercial huskers use a car tire rotating against a metal mesh. Some take a thick plywood board and drill a nut-sized hole in it (from one to two inches in diameter) and smash the nut through using a hammer. The nut goes through and the husk remains behind.[11]

While the flavor of the Juglans nigra kernel is prized, the difficulty in preparing it may account for the wider popularity and availability of the Persian walnut.

Dye

Black walnut drupes contain juglone (5-hydroxy-1,4-naphthoquinone), plumbagin (yellow quinone pigments), and tannin. These compounds cause walnuts to stain cars, sidewalks, porches, and patios, in addition to the hands of anyone attempting to shell them.[12] The brownish-black dye was used by early American settlers to dye hair.[13] According to Eastern Trees in the Petersen Guide series, black walnuts make a yellowish-brown dye, not brownish-black. The apparent confusion is easily explained by the fact that the liquid (dye) obtained from the inner husk becomes increasingly darker over time, as the outer skin darkens from light green to black. Extracts of the outer, soft part of the drupe are still used as a natural dye for handicrafts.[14] The tannins present in walnuts act as a mordant, aiding in the dyeing process,[15][16] and are usable as a dark ink or wood stain.[17]

Industrial

Walnut shells are often used as an abrasive in sand blasting or other circumstances where a medium hardness grit is required. The hard black walnut shell is also used commercially in abrasive cleaning, a filtering agent in scrubbers in smoke stacks, cleaning jet engines, cosmetics, and oil well drilling and water filtration.[6]

Wood

Black walnut wood showing the color and grain

Black walnut is highly prized for its dark-colored, straight grained, true heartwood. It is heavy, strong, shock resistant and yet can be easily split and worked. Along with cedars (Thuja spp.), chestnut (Castanea spp.), and black locust (Robinia pseudoacacia) black walnut is one of the most durable hardwoods in the US.[6] The wood can be kiln dried and holds its shape well after seasoning which makes this wood even more attractive for wood working.[6]

Walnut wood has historically been used for gun stocks, furniture, flooring, paddles, coffins, and a variety of other wood products.[6] Due to its value, forestry officials often are called on to track down walnut poachers; in 2004, DNA testing was used to solve one such poaching case, involving a 55-foot (16-m) tree worth US$2,500. Black walnut has a density of 660 kg per cubic meter (41.2 lb/cubic foot),[18] which makes it less dense than oak.

Pests

Maggots (larvae of Rhagoletis completa and Rhagoletis suavis) in the husk are common, though more a nuisance than a serious problem for amateurs, who may simply remove the affected husk as soon as infestation is noticed. The maggots develop entirely within the husk, thus the quality of the nutmeat is not affected.[19] However, infestations of maggots are undesirable because they make the husk difficult to remove and are unsightly. Maggots can be serious for commercial walnut growers, who tend to use chemical treatments to prevent damage to the crop.[20] Some organic controls also exist, such as removing and disposing of infested nuts.[21]

The walnut curculio (Conotrachelus retentus) grows to 5 millimetres (3⁄16 in) long as an adult. The adult sucks plant juices through a snout. The eggs are laid in fruits in the spring and summer. Many nuts are lost due to damage from the larvae, which burrow through the nut shell.[22]

Black walnut is affected by European canker (Neonectria galligena). The infection spreads slowly but infected trees eventually die.[6]

The walnut caterpillar (Datana integerrima) and fall webworm (Hyphantria cunea) are two of the most serious pests, they commonly eat the foliage in midsummer and continue into autumn.

Codling moth (Cydia pomonella) larvae eat walnut kernels, as well as apple and pear seeds.[23]

Important leaf sucking insects include species of aphids and plant lice including (Monellia spp. and Monelliopsis spp.),which suck the juices from leaves and often deposit a sticky substance called "honey-dew" on the leaf surface that may turn black and prevent photosynthesis; and the walnut lace bug (Corythucha juglandis),which causes damage when the adults and nymphs suck the sap from the lower surfaces of walnut leaflets.[4]

A disease complex known as thousand cankers disease has been threatening black walnut in several western states.[24] This disease has recently been discovered in Tennessee, and could potentially have devastating effects on the species in the eastern United States.[25] Vectored by the walnut twig beetle (Pityophthorus juglandis), Geosmithia morbida spreads into the wood around the galleries carved by the small beetles. The fungus causes cankers that inhibit the movement of nutrients in black walnut, leading to crown and branch dieback, and ultimately death.[26]

Allelopathy

Black walnut is allelopathic as it excretes chemicals into its environment which harm competition. While many species of plants are allelopathic, walnuts are particularly famous for it, records of walnut toxicity to other plants have been observed as far back as the first century when Pliny the Elder wrote: "The shadow of walnut trees is poison to all plants within its compass."[27] Walnuts have since been observed as being toxic to many plants including herbaceous and woody plants

Like other walnuts, the roots, innerbark, nut husks, and leaves contain a nontoxic chemical called hydrojuglone,[27] when exposed to air or soil compounds it is oxidized into juglone which is biologically active and acts as a respiratory inhibitor to some plants. Juglone is poorly soluble in water and does not move far in the soil and will stay most concentrated in the soil directly beneath the tree.[28] Even after a tree is removed the soil where the roots once were will still contain juglone for several years after the tree is removed as more juglone will be released as the roots decay.[28] Well drained and aerated soils will host a healthy community of soil microbes and these microbes will help to break down the juglone.

Symptoms of juglone poisoning include foliar yellowing and wilting.[28] A number of plants are particularly sensitive including: apples, tomatoes, pines, and birch are poisoned by juglone, and should not be planted in proximity to a black walnut.[4][29]

Interaction with horses

Horses are susceptible to laminitis from exposure to black walnut wood in bedding.[30]

Alternative medicine

Black walnut has been promoted as a potential cancer cure by alternative medicine practitioners, on the basis it kills a "parasite" responsible for the disease. According to the American Cancer Society, "available scientific evidence does not support claims that hulls from black walnuts remove parasites from the intestinal tract or that they are effective in treating cancer or any other disease".[31]

Largest trees

The largest known living black walnut tree is on Sauvie Island, Oregon.

The US national champion black walnut is on a residential property in Sauvie Island, Oregon. It is 8 ft 7 in (2.62 m) diameter at breast height and 112 ft (34 m) tall, with a crown spread of 144 feet (44 m).[32]

The largest black walnut in Europe is located in the Castle Park in the city of Sered, Slovakia. It has a circumference of 6.30 m (20 ft 8 in), height of 25 m (82 ft) and estimated age of 300 years. [33]

See also

References

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  1. 1 2 Peterson, George A. Petrides ; illustrations by George A. Petrides, Roger Tory (1986). A field guide to trees and shrubs : northeastern and north-central United States and southeastern and south-central Canada (2nd ed.). Boston: Houghton Mifflin. ISBN 0-395-13651-2.
  2. 1 2 3 4 5 6 Dirr, Michael A (1990). Manual of woody landscape plants. (4. ed., rev. ed.). Champaign, Illinois: Stipes Publishing Company. ISBN 0-87563-344-7.
  3. ↑ Rhoads, Ann; Block, Timothy. The Plants of Pennsylvania (2 ed.). Philadelphia Pa: University of Pennsylvania press. ISBN 978-0-8122-4003-0.
  4. 1 2 3 4 5 6 7 8 9 10 11 12 Williams, Robert D. (1990). "Juglans nigra". In Burns, Russell M.; Honkala, Barbara H. Hardwoods. Silvics of North America. Washington, D.C.: United States Forest Service (USFS), United States Department of Agriculture (USDA). 2. Retrieved 2016-06-29 – via Northeastern Area State and Private Forestry (www.na.fs.fed.us).
  5. ↑ "Juglans nigra". Flora of North America (FNA). Missouri Botanical Garden – via eFloras.org.
  6. 1 2 3 4 5 6 7 8 9 10 "Juglans nigra". www.fs.fed.us. Retrieved 2016-06-29.
  7. ↑ "Juglans microcarpa". www.fs.fed.us. Retrieved 2016-06-29.
  8. ↑ RHS A-Z encyclopedia of garden plants. United Kingdom: Dorling Kindersley. 2008. p. 1136. ISBN 1-4053-3296-4.
  9. ↑ "Juglans nigra". Royal Horticultural Society. Retrieved 23 July 2013.
  10. ↑ Senter, S. D., Horvat, R. J., and Forbus, W. R.: "GLC-MS Analysis of Fatty Acids From Five Black Walnut Cultivars." Journal of Food Science 47(5) pp 1753, 1755 (1982)
  11. ↑ Mason, Sandra. "Preparing Black Walnuts for Eating". University of Illinois Extension. Retrieved 2014-07-26.
  12. ↑ Black Walnuts Drug Information
  13. ↑ Nuts with High Fat Content:Black Walnuts
  14. ↑ Black Walnut Basket Dye
  15. ↑ Fixing natural dyes from walnuts, goldenrod, sassafras and poke weed in cotton
  16. ↑ Dyeing with Tannic Acid and Iron: Walnut Husks (2005)
  17. ↑ Making Walnut Ink. Madame Elizabeth de Nevell.
  18. ↑ Niche Timbers Black Walnut
  19. ↑ Walnut Husk Maggot, Rhagoletis suavis (Loew) and Walnut Husk Fly, Rhagoletis completa Cresson
  20. ↑ Walnut Husk Maggot. Ontario Ministry of Agriculture, Food and Rural Affairs.
  21. ↑ Walnut Husk Fly.
  22. ↑ Barbara C. Weber, Robert L. Anderson, and William H. Hoffard. How to diagnose black walnut damage. USDA Forest Service. General Technical Report NC-57.
  23. ↑ University of California. Agriculture and Natural Resources. Publication 7412. Codling Moth.
  24. ↑ Purdue University: Purdue Pest & Plant Diagnostic Laboratory. Pest Alert: Walnut Twig Beetle and Thousand Cankers Disease of Black Walnut
  25. ↑ Bill Poovey. Black walnut tree thousand canker first in East US. Times Union. Posted July 30, 2010.
  26. ↑ http://www.clemson.edu/public/regulatory/plant_industry/pest_nursery_programs/invasive_exotic_programs/pest_alerts/walnut_twig_beetle.html
  27. 1 2 Rietvelt, W. J (1983). "ALLELOPATHIC EFFECTS OF JUGLONE ON GERMINATION AND GROWTH OF SEVERAL HERBACEOUS AND WOODY SPECIES" (PDF). Journal of chemical ecology. 9 (2). Retrieved 2 July 2016.
  28. 1 2 3 "black walnut toxicity" (PDF). Retrieved 30 June 2016.
  29. ↑ "Black Walnut Toxicity". West Virginia University. Retrieved 3 July 2014.
  30. ↑ "Laminitis Caused by Black Walnut Wood Residues" (PDF). Purdue University. January 2005. Retrieved 9 March 2009.
  31. ↑ "Black Walnut". American Cancer Society. April 2011. Retrieved September 2013. Check date values in: |access-date= (help)
  32. ↑ Oregon Champion Tree Registry.
  33. ↑ Sered City has a unique tree Juglans nigra tree nominated in the contest of 2012
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