Propagation of black walnut trees is possible from nuts that contain the outer husks. According to the University of Minnesota's extension service, the seeds or nuts have a better chance of germination if the outer husk is peeled away. Black walnut trees are valuable for both the nuts the tree produces, and the lumber from older trees. Black walnut trees that reach a diameter of 12 inches, measured 4 ½ feet from the ground, are ready to be harvested for lumber. Time of growth is fully dependent on site selection and amount of annual rainfall.
Collect the black walnuts immediately after they have hit the ground. Walnuts that sit on the soil for too long will develop rot, or worms will begin to enter through the outer green husk.
Place the nuts in a bucket full of water. Discard any that float. If you so desire you can stop here and go on to Step 5, as black walnuts with the outer husk planted in the soil will germinate, but not as well as the peeled nuts.
Put on rubber gloves. Peel the outer green husk away from the hard shell. The outer husks will be easier to peel after the nuts have soaked in the water for a short period of time.
Rinse the peeled nuts in a bucket of clean water. Discard any nuts that are floating. The sinker nuts will have more nutmeat to germinate.
Dry the walnuts on an open space, protected from predators. Place the nuts in a plastic bag after the outer shell is fully dry. In the case of black walnuts with the outer husk intact, the husk will turn from a vibrant green color to a dark black when dried.
Set the plastic bag in the refrigerator for 90 days to 120 days where the temperature will remain between 34 degrees F to 41 degrees F. This process is called stratification. Many seeds require cold treatment or stratification to germinate.
Plant the black walnuts in the field or growing area after all danger of frost has passed. Dig a singular hole approximately 1- to 2-inches deep. Place one nut per hole. Cover with soil. Place the walnuts in a grid pattern approximately 12 feet by 12 feet for best results in timber and nut production.