Black walnut trees are native to the eastern half of the United States. They are slow-growing trees that live a long time. Black walnut trees are valuable as timber trees as well as for nut production. Black walnuts are rather messy to collect and to process. The extremely hard shells are difficult to crack. However, the nutmeats are delicious and very nutritious. If you don't have a black walnut tree in your yard, you can gather the nuts free on public lands.
Wait until the black walnuts begin to drop from the tree naturally in September and October. The nuts look like small green tennis balls when they first fall; after they have been on the ground several days the green husks begin to turn brown and leathery.
Gather the nuts with green husks and put them in a bucket or other container. Black walnut juice from the husks will stain anything it touches, even your skin, so wear gloves and use old containers that you don't mind being stained.
Remove the husks from the black walnuts. There are several different ways to do this. Some people spread the walnuts out on a driveway and drive back and forth over them to loosen the husks. If you have a small number of nuts, you can stomp them with heavy boots. You can also score the husk with a sharp knife and twist apart the sections of husk; however, this requires strong hands, and the sharp blade is a safety hazard.
Clean the residue of the husks from the nuts by soaking the nuts for a few minutes in a bucket of water, and then agitating them. Dump the water and repeat the agitation process if necessary. Do not pour the walnut water on your garden or on plants, and do not put the husks on your compost pile. They contain the toxic chemical compound juglone, which kills plants and earthworms.
Spread the black walnuts to dry after they are washed. Allow two to three weeks for them to dry and cure before you crack the shells.
Crack black walnuts using a vise for the first opening crack, and a hammer or heavy-duty electrical cutters to crack the smaller pieces of shell. Shell the nuts, and store the meats in the refrigerator for two to three weeks or in the freezer for eight months or more. Due to the high level of oils they contain, shelled black walnuts turn rancid quickly if left unrefrigerated. Black walnuts can be stored unshelled in a cool, dark place for about two months before they begin to turn rancid.