For most large trees the nuts are too difficult to reach and can only be practically collected after they fall from the tree. Husks must be removed before you store black walnuts and are easier to remove when husking before this green husk turns into a hard black seed cover.
Don't pile walnuts in husks for long periods of time or let the husks deteriorate. Aging walnut husk's juices can penetrate the shell and discolor the nutmeat and give the nut an undesirable flavor. Husk them as soon as is possible after they drop.