Knock the nuts from the tree when the green hulls begin to split and the packing tissue between and around the kernel halves has just started to turn brown.
Remove the hulls as soon as you can. There are several ways to remove the hulls: Use a knife, stomp and roll the nuts with your foot, roll over them with the car tire, between two boards or work them over a rough screen to loosen and remove the hulls.
If the hulls stick tightly to the shells, moisten them and cover with a moist tarp or burlap sheet for several days to loosen.
Particularly with black walnuts, but also with the others, wear gloves when handling the hulls to avoid staining your hands.