Walnuts are harvested in the fall, normally from mid-September to early November. The harvest begins when the nuts have matured and a high percentage of nuts on the tree have split hulls, usually a small amount of nuts have already started to naturally fall to the ground. This last phase of maturation and hull split can be hastened by applying an ethylene-producing compound, such as ethephon.
The nuts are removed from the tree using a mechanical shaker, a machine that grasps the trunk and shakes the whole tree. The nuts drop to the ground, are then swept into windrows and picked up with harvest machinery. This operation is completed quickly to reduce the time nuts remain on the ground.
Harvested nuts are taken to a huller that removes the green hulls from the shell with wet scrubbers and dried in gas dryers for 24 hours or less (until the nuts reach 8% moisture content). When dry, the nuts are ready for storage or processing. Processors typically buy walnuts in-shell and then crack, grade, and package them for marketing.