Black walnut

Black walnut (Juglans nigra) is a North American flowering tree that is related to the hickory. Dendrologists, and others who fancy deciduous plants and trees, appreciate the fact that these stately giants are outstanding shade providers. However, there is a long-standing belief that black walnut trees also protect the home from lightning strikes. While some believe this is due to the presence of an abundance of minerals in the timber that act as electrical conductors, it may also be due to the fact that mature black walnut trees can reach up to 60 feet in height. Whatever the reason, these trees have apparently saved many abodes from disaster since it was once commonplace to adopt a strategy of planting groves of them in proximity. In fact, the next time you visit a historic residence or farmstead, conduct a visual scan of the property. Chances are you’ll see several black walnut trees standing ready to deter misfortune. As an added bonus, early homesteaders knew that the presence of black walnut on a potential stake of property indicated that the land was fertile since these trees require a rich, slightly alkaline, and well-drained soil in order to thrive.

The hardwood of black walnut is highly valued for its exceptional beauty and durability. The wood is particularly dense, yet it splits readily and is easier to machine than many other types of wood. These qualities have inspired seafarers, gun manufacturers, and undertakers to use the wood to make boats, gunstocks, and coffins from the wood. Of course, many specimens of fine antique furniture are also made of this material. In fact, until mahogany came into fashion in the late 18th century, black walnut was the wood of choice of furniture makers. During World War I, the husks of the tree were used to produce a high-grade charcoal to filter gas masks. In the mid-20th century, various parts of the tree were used to make an insecticide and herbicide, the effectiveness of which was owing to the presence of juglone.

Juglone, chemically known as 5-hydroxy-alphanapthaquinone, is classified an allelochemical, meaning that it negatively affects the growth of certain neighboring plants by impairing enzymatic processes necessary for survival. This is why some gardeners consider black walnut to be a hindrance in terms of limiting options in landscaping. Regardless, juglone is potent stuff. It’s the reason that black walnut trees are rarely impacted by disease and explains why insects won’t even come into contact with the leaves.

This same substance is what has earned black walnut a place in herbal medicine. In fact, an extract made from the leaves and dubbed “vegetable arsenic” is considered an effective topical remedy for eczema and other skin disorders. However, most herbalists rely on obtaining the beneficial properties of juglone from the hull of the nut, which is ground into a fine powder and prepared as a tincture, salve, or tea. The primary use of black walnut hull is to rid the body of intestinal parasites. Toward that goal, juglone is assisted by the presence of additional quinine compounds and tannins, such as galloyl glucose and ellagitannins.

Other constituents found in black walnut hull include alkaloids, trace minerals, linolenic acid, iodine, and ascorbic acid (vitamin C). As such, traditional uses of this botanical include the treatment of high cholesterol, high blood pressure, hypothyroidism, digestive disorders, asthma, and other respiratory conditions. Topically, black walnut hull preparations are used to address acne, warts, poison ivy, hemorrhoids, cold sores associated with the herpes virus, and fungal infections of the skin, such as ringworm. The properties of black walnut are also thought to promote detoxification of the body when taken internally. In fact, many naturopathic physicians suspect that the various agents found in black walnut hull may enhance the transport and delivery of oxygen to tissue cells, thereby accelerating the elimination of toxins.

Generally, there are no known adverse side effects associated with black walnut hull. However, a few words of caution are warranted. First, Dan Kenner and Yves Requena, the authors of Botanical Medicine: A European Professional Perspective (Paradigm Publications, 1996) do not recommend the internal use of black walnut hull to treat any condition when there is fever present. In addition, juglone can damage the liver or kidneys in humans if consumed in very high doses over a long period of time. Therefore, it is generally recommended that black walnut hull be used on an alternating basis, specifically up to two weeks at any one time. It should also be noted that dogs and horses should not come into contact with black walnut hull pieces due to potential allergic reaction.