Black walnut is an important tree commercially, as the wood is a deep brown color and easily worked.

Walnut trees are grown for lumber and food, and processors have found additional markets for even the tough outer hulls by finely grinding them for use in products such as abrasive cleansers.

[6] Visually, black walnut is similar to the butternut (Juglans cinerea) in leaf shape, and the range also overlaps significantly.

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.

It is absent from the coastal plain south of North Carolina as well as the Mississippi Valley, and does not occur in the northern tier of the eastern US, where the frost-free season is too short for the nuts to develop.

Black walnut is one of the most abundant trees in the eastern US, particularly the Northeast, and its numbers are increasing due to epidemics that have affected other tree species, including emerald ash borer, chestnut blight, butternut canker, wooly hemlock adelgid, dogwood anthracnose, Dutch elm disease, and spongy moth infestations.

The aggressive competitive strategy of black walnut such as its fast growth, alleopathic chemicals, and rodent-dispersed seeds, have also contributed.

[6] 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.

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.

[8] 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.

), 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.

The fungus causes cankers that inhibit the movement of nutrients in black walnut, leading to crown and branch dieback, and ultimately death.

[17] While black walnut is considered allelopathic, meaning it excretes chemicals into its environment that harm competition, research from 2019 has questioned whether this long-held belief holds up to scientifically rigorous examination.

Many publications that have repeated claims of black walnut allelopathy cite a very limited set of dated research literature, which has not held up to scientific scrutiny.

"[19] Like other walnuts, the roots, inner bark, nut husks, and leaves contain a nontoxic chemical called hydrojuglone;[19] when exposed to air or soil compounds it is oxidized into juglone that is biologically active and acts as a respiratory inhibitor to some plants.

Apples, tomatoes, pines, and birch are poisoned by juglone, and as a precaution, should not be planted in proximity to a black walnut.

[22] 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.

[28] NPR affiliate KCUR stated in an article that "Ralph Hammons began the company in 1946 with a nut cracking machine acquired from Tennessee.

"[29] The Stockton Black Walnut Festival, which has been held annually since 1961, "brings the community together for a 3-day event jam-packed with activities including a carnival, tractor pull, nut roll and 2-hour parade," stated Alexa Hodges in a VOX article.

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.

[5] The shell itself is thicker than that of the English walnut, and there are additional, thick internal walls tightly surrounding the nutmeat.

[32] 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 English walnut.

Consumers include black walnuts in traditional treats, such as cakes, cookies, fudge, and pies, during the fall holiday season.

These compounds cause walnuts to stain cars, sidewalks, porches, and patios, in addition to the hands of anyone attempting to shell them.

[42][better source needed] 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.

[43] The tannins present in walnuts act as a mordant, aiding in the dyeing process,[44][45] and are usable as a dark ink or wood stain.

[48] The tallest black walnut in Europe is located in the Woluwe Park in the city of Sint-Pieters-Woluwe, Brussels, Belgium.