To harvest butternuts, remove the nuts from the tree when the outer shell splits and begins to turn brown. Wearing gloves, remove the hulls manually, or press the nuts between two boards to remove the outer hull. If the hulls are very difficult to remove, place the nuts on a sheet of damp burlap or tarp for several days to loosen the outer hull. After removing the hull, place the nuts in a warm location to dry.
Other options to remove the hull include rubbing the butternuts on a wire screen, stepping on the nuts to loosen the outer hull, or driving over the nuts to loosen the hull. After hulling butternuts, remove any fibers on the outside of the shell, and place the nuts in a bucket of clean water. Discard nuts that float.
Place the clean, unshelled butternuts on wire trays in a well-ventilated area that is protected from pests, and allow the nuts to dry for several weeks. When the nut rattles inside the shell, it is sufficiently dry.
Crack the shells open with a nutcracker to harvest the nuts, or store unshelled nuts in a cool, dry location with adequate ventilation. Use unshelled nuts within several months to prevent spoilage. Store the shelled nuts in the freezer for up to one year.