Black walnuts are harvested from the black walnut tree, which is native to North America. If you find yourself to be fortunate enough to have a black walnut tree in your yard, you can harvest the nuts yourself and prepare them for storage. Depending upon your chosen storage method, black walnuts can keep from three weeks to two years. Storing them requires only a little prep work.
Put on a pair of garden gloves and remove the husks from the black walnuts if they have not been removed already. The gloves will protect your hands from stains that can come from the residue of the hulls. To hull the black walnuts you can pound them with a hammer, stomp on them or roll them in a hand cement mixer. Be sure to wear safety goggles. If your nuts are already hulled, cleaned and ready for storage, move on to step 4.
Lay the batch of hulled nuts out on the ground or your driveway and hose them down with a garden hose. If you only have a few nuts you can use a sink, but it should be done in a garage or utility sink, as freshly hulled black walnut shells can leave dark stains on items they come in touch with, even skin.
Stack the nuts in a shallow, cardboard box. Make sure the stack is no more than three nuts high to allow for proper air circulation. Place the box of nuts in a cool, dry area out of direct light for 14 days. This cures the black walnuts and is the final preparation for storage.
Place the black walnuts, with shells still on, in a wire basket or baskets. This allows the air to circulate around the nuts, which helps prevent mildew and mold growth.
Store the baskets of black walnuts in a humid area. The University of Minnesota Extension recommends that the humidity be around 70 percent. If the nuts are kept in an area that is too dry, the shells may crack, which can spoil the nutmeat. If you shell the walnuts and wish to store the nutmeat, go on to step 6.
Shell the nuts and place the nutmeats on an ungreased cookie sheet. Bake the nutmeats in a 215-degree oven for 15 minutes.
Remove from the oven and allow them to cool on the cookie sheet. When the nutmeats have cooled, place them in a sealed container. You can store the sealed container in the freezer for up to two years; the refrigerator for up to nine months or at room temperature for up to three weeks.