Black Walnut

Also Known As: Jupiter’s Nuts and Carya

Botanical Name: Juglans Nigra

Family Name: Juglandaceae

Native To: Eastern North America

Parts To Use: Leaves, Bark, Nuts, and Green Hull

How It’s Used: Taken by mouth to treat parasitic worm infections and certain other infections including diphtheria and syphilis.

Harvesting: Black walnuts can be gathered after they’ve fallen from the tree in autumn. The thick outer husk will need to be cracked with a rock or hammer, then the nut removed. The nut can be incredibly staining, so use a stiff brush for assistance. Let the nuts air dry before use.

Although walnut trees produce a bounty of edible nuts, they are generally grown for their beautifully-grained hardwood.

Approximately 20 species and 400 cultivars of Juglans dot landscapes and forests across the world. The ranks of walnuts include the Persian or English walnut (Juglans regia), a native of southeast Europe and western Asia, and the cultivar that produces the majority of commercially-prepared walnuts. J. regia has a milder taste than J. nigra, but in herbalism, the plants are considered of equal value. More than 11,000 tons of black walnuts are harvested annually in the United States, with about half of those nuts going directly to ice cream and baking manufacturers (Small, 2014). 

Though they produce a bounty of edible nuts, most walnut trees are grown for their beautifully-grained hardwood. Transformed into fine furniture, gunstocks, and pianos, walnut timber is a coveted resource the world over (Small, 2014).   

It isn’t just the timber that has market value, however. Walnut shells may be notoriously hard to crack, but their strength makes them fit for a variety of commercial uses. In WWI, for example, crushed black walnut shells were used to create filters for gas masks and were later used to create an abrasive cleaner for aircraft pistons and cylinder heads. Walnut shells are used in contemporary applications, too. They are ground and used to clean and polish metal and are extensively used in the process of sealing leaks on oil rigs. The shells are also used as an ingredient in paints, explosives, and cosmetics (Small, 2014).  

Juglans nigra, also known as eastern black walnut, is the tallest and most long-lived of the Juglans species, occasionally living as long as 250 years when conditions prove hospitable. Juglans nigra prefers rich, loamy soil and often grows in ditches and along riverbeds. Dutch settlers who came to North America looked for eastern black walnut trees when deciding where to live, since these trees indicated the presence of good quality soil (Small, 2014).

Black walnuts were considered a good omen as far back as the Middle Ages. At weddings, the groom frequently threw black walnuts to signify his maturity. Walnuts were also used as a kind of talisman to ward off lightning, fevers, witchcraft, and epileptic seizures (Janick and Pauli, 2008). 

Black walnuts have historically been collected as an important food source for a number of Native North American tribes. The Apache, Navajo, Northern Tepehuan, Tewa, Tohono, Tohono O’odham, Walapi, and Yavapai peoples have all gathered and stored black walnuts for sustenance over the winter (Austin, 2010). Stores of black walnuts dating to 2000 BCE have been found at several archeological sites in the Great Lakes region, affirming their importance as a storage crop (Small, 2014). 

In addition to eating the nuts for a source of protein, various Native American tribes such as the Iriqouis have tradtionally made walnut milk by grinding the kernels and adding water. They have also pressed black walnuts and used the oil in prepared foods (Small, 2014).  

The timber, nutmeats, and shells of the black walnut may have broad commercial and cultural uses, but black walnut also has a lengthy history of use in herbal traditions. In the Doctrine of Signatures, the Greeks believed that the shell of a black walnut resembled the human skull, and associated the nut with the human brain. Accordingly, the Greeks used black walnuts to ease headaches and issues of mental illness (Janick and Pauli, 2008). 

The Cherokee, Delaware, Iroquois and Meskwaki tribes have a history of chewing the bark of the black walnut tree for mouth sores and toothaches and crushing the husks and leaves for ringworm infections. An infusion of nut shells has been used for skin inflammations, and charred black walnut sticks were applied to burns, wounds, and insect bites to soothe itching or inflammation (Meuninck, 2008).  

Black walnut is a known alterative, anthelmintic, antifungal, antiseptic, astringent, insecticide, laxative, and parasiticide. The green hull of the black walnut is particularly prized among contemporary herbalists; it is used to cleanse the blood and intestines and for skin conditions, including eczema, impetigo, and other kinds of dermatitis (Ritchason, 1995). 

Rosemary Gladstar (2001/2008) explains that black walnut is effective against fungal infections, an action owing to its high juglone content. Interestingly, it is walnut’s juglone that makes it toxic to many other plants growing nearby.

According to Gladstar (2001/2008), black walnut tincture is also appropriate for gastrointestinal problems, such as diarrhea and constipation caused by intestinal parasites, including giardia and candida. Topically, a black walnut tincture is used on herpes lesions and cold sores.

Clinically, black walnut is well researched, though most studies focus on the nuts as a source of nutrition, particularly as a heart protectant. In a randomized, controlled, single-blind, crossover clinical trial conducted in 2012, forty-six overweight adults with signs of metabolic syndrome (a precursor of diabetes and cardiovascular disease), were randomly assigned to two 8-week sequences of a walnut-enriched diet (Katz et al., 2012). 

Throughout the study, participants consumed 56 grams of shelled, unroasted walnuts per day, while a control group did not eat any walnuts. At periodic intervals, participants underwent endothelial function testing following an 8-hour fast.

Endothelial function was measured in participants’ right brachial artery, using a high-frequency ultrasound machine. A resting scan was performed, and arterial flow velocity was measured (the percentage change of brachial artery diameter from before cuff inflation to 60 seconds after cuff release.) These tests revealed a significant change in the flow-mediated vasodilation in the brachial artery of the group who consumed walnuts, as compared to the control group (1.4% ± 2.4% versus 0.3% ± 1.5%; p = 0.019)

Increasingly, endothelial function is being viewed as a predictive marker of one’s susceptibility to possible cardiac events. The positive changes in endothelial function in this study make a strong case for including walnuts as part of a healthy diet.

Not only are walnuts good for the heart, but they also show promise as an agent in the fight against drug-resistant bacteria. Iqbal et al. (2013) added an aqueous extract of J. regia to Mueller-Hinton agar, followed by drug resistant Salmonella typhi or enteropathogenic E. coli. Researchers then placed paper discs with different classes of antibiotics on the agar surface. As a control, bacteria were incubated with J. regia extract or antibiotics alone. 

The results demonstrated a significantly larger zone of inhibition (>30%) around several of the antibiotics tested, compared with J. regia or antibiotics alone. In other words, J. regia works in tandem with selected antibiotics to inhibit drug-resistant bacteria. Though researchers have yet to identify the precise biological mechanism at work, it’s clear that J. regia has the potential to work synergistically with other medicines.   

In a similar study, black walnut extract was selectively active against Gram-positive bacteria. Significantly, J. regia demonstrated strong anti-staphylococcal activity that led to the changes in bacterial cell morphology (Farooqui et al., 2015).