Harvest Season

• Black walnuts undergo their ripening process toward the end of August into September, according to the University of Minnesota. The University of Illinois suggests late September as a good time to begin harvesting the ripened walnuts.
  
  

Ripeness

• Harvesters can tell whether a black walnut has become ripe by looking at its color, according to the University of Minnesota. Ripe black walnuts will have yellow-green husks instead of the solid green color of the unripened nuts. Ripe nuts will also retain indentations when the harvester presses on them.
  
  

Collection Methods

• Mature black walnuts will often simply drop from the tree to the ground, according to the University of Illinois. As long as the nuts appear mature, however, harvesters can shake the tree limbs or use a pole to remove them from the tree. The outer husks can deposit stains, so harvesters should wear gloves to protect their hands.