Native Plants

NATIVE PLANTS

The Black Walnut

Juglans nigra

- Diana L. Cassel, Ph.D.

The black walnut, also known as the American walnut, is native to eastern North America. Those greenish “tennis balls” you see in the park in the fall are the fruits of the black walnut. This big deciduous (loses its leaves in the fall) hardwood can reach 150 feet in height in a good site, but in a forest only 70 to 80 feet. The brown to gray-black bark is thick and deeply furrowed. There are black walnut trees growing near the Upper Farm Road along the railroad tracks just down the hill from the Springhouse. They are interspersed among some non-native tree of heaven specimens. Note that although the leaves of these trees appear similar, the bark is very different, with the black walnut blackish rough bark contrasting with the grayish smooth bark of the tree of heaven. The compound leaves of the black walnut are 1 to 2 feet long, with the 15 to 23 leaflets arranged alternate pinnately, i.e., on opposite sides of a long axis.

The root system is deep and wide. The roots, as well as the leaves, bark and nut husks, produce a toxic substance called juglone, which prevents some plants from growing nearby. These include the white pine, the red pine, the Scotch pine, the paper birch, apple trees and especially the tomato. In these susceptible plants, juglone causes yellowing, wilting and death. Black walnuts are shade intolerant and prefer full sun. The straight-grained hard wood of black walnuts is used for furniture, gunstocks and veneer. The nuts are eaten by man and other animals and oil is pressed from the nuts.

Black Walnut Reproduction

Black walnuts are monoecious, which means separate male and female flowers are borne on the same tree. The flowers appear from mid-April to mid-June. The male flowers are slender catkins that arise from the previous year’s growth. Catkins are slender cylinders of flower clusters closely packed along a stem that frequently droops. In the black walnut, catkins produce pollen. The female flowers occur at the termini of short spikes on the current year’s shoots. They look like a little pear (ovary) with 2 V-shaped antennae (stigmas). The flowering is dichogamous, which means either the female flower (more common) or the male flower develops first, followed by the other. This means that the female flowers, usually but not always, are fertilized by the pollen from a different tree. The stigmas capture the pollen and the ovaries develop first into the husk (yellowish green), then the corrugated shell and then the seed (nutmeat). The husk surrounding the nut (shell and seed) equals the fruit, which drops from the tree soon after the leaves do in the fall. During ripening, the husk turns from green to brown or black and softens. Various wildlife bury the nuts and those not eaten will germinate during the first or second spring after the freezing and thawing of winter.

Harvesting Black Walnuts – A Comedy

Harvesting black walnuts takes a whole lot of effort. You must really want to! First, they have to be hulled – that means the husks have to be removed. It is best to do this when they are green. Gloves should be worn because the dye from the husks stains – and does not come off for about 2 weeks no matter how much you wash your hands. I can attest to that! Husks can be removed by hammering side to side (wearing safety glasses), by soaking and then peeling, by using a hand-operated corn sheller or by stomping on them wearing old shoes over pavement (which will be stained). Another tried and true way is to drill a nut-sized hole in a heavy plywood board and then hammer the nut through – the nut goes through and the husk does not. After the husks are removed, the nuts are rinsed (outdoors because they stain, too) and then the clean nuts must be cured for 2 weeks in a cool, dry place out of the sun. This allows flavors to develop. To shell the nuts, they are soaked in water for 24 hours, drained and then soaked for 2 more hours. Cracking the black walnuts requires extreme force. Some people spread them out on the driveway and drive a car over them. Or you can crack the shell with a large rock, a vise, a heavy hammer or a heavy-duty nutcracker (you can find a Black Walnut Cracker at C.E. Potter in Sapula, OK – 918-224-0567). Even after cracking the shell, it is still difficult to get the meat out. Commercially, this is all done with machines. For example, a car tire rotating against a metal mesh is used in commercial huskers. Now we can ask, “How do the animals crack the nut?” I have not found any information on that subject!

Other Interesting Walnut Facts

Black walnuts belong to the walnut family, Juglandaceae. The Romans believed that the gods loved walnuts. The genus name Juglans is from a contraction of the Latin for Jupiter and nut, thus Jupiter’s nut, or nut of the gods. The genus, Juglans, comprises 15 edible species. The most widely used species is Juglans regia, also known as the English, Persian or common walnut (the one we see in the grocery stores). At Roman weddings, the groom threw walnuts to the guests; the walnuts were believed to bring good health and promote fertility. During the Middle Ages in Europe, walnuts were believed to thwart witchcraft, the evil eye, and lightening as well as protect against fevers and epilepsy.

In North America, many of the native groups used the bark of the native black walnut, J. nigra (“nigra” means black), for various purposes. The Cherokee among others used it in a tea to treat constipation and chewed it for toothache pain. The Cherokee and the Chippewa made brown and black dyes from the bark. A paste made from the leaves and husk of the fruit was used to treat ringworm by the Comanche. Other uses of black walnut by several native groups included treatments for athlete’s foot and hemorrhoids and as an insecticide. I wonder if staining was a problem for the native Americans during these treatments.

What do we know today about the walnut? Walnuts are a high protein food with a high fat (oil) content. They are a rich source of alpha linolenic acid (an omega 3, polyunsaturated fatty acid) and Vitamin E, a powerful antioxidant. They are good for you when eaten in reasonable quantities (watch those calories!). Like all foods high in unsaturated fat, they can turn rancid if not stored properly in a cool place. Black walnuts have a strong flavor, which has been described as “rich, smoky….with a hint of wine.” They can be eaten raw or cooked in any recipe with nuts listed as an ingredient, but their strong flavor has to be taken into consideration or it will overwhelm everything – using 1 part black walnuts to 3 parts English walnuts (the common type) is a good idea. Here is a recipe that uses black walnuts straight – it’s from The Nut Factory (www.thenutfactory.com):

Black Walnut and Wild Rice Pilaf

1 cup uncooked wild rice

¼ cup butter

1 cup sliced mushrooms

½ cup chopped green pepper

1 tsp garlic salt

½ cup black walnuts

Cook the wild rice according to package directions. Melt the butter and sauté the black walnuts, mushrooms, onion and green pepper about 3 minutes, or until the vegetables soften slightly. Add the wild rice and garlic salt and continue cooking, stirring several times, until the wild rice is heated through. Serves 4 to 6. The garlic and black walnuts probably battle over taste supremacy in this recipe!

Information for this article came from the USDA’s Natural Resources Conservation Service, University of Minnesota Extension, the US Forest Service, the Department of Forestry, College of Natural Resources at Virginia Tech, from Home Cooking at about.com, Inc. and from walking in NFP and observing first-hand. Aren’t we lucky we have NFP?

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