Black walnut trees (Juglans nigra) are a magnet for family gatherings in autumn, when the delicious nuts they drop are treasures for children to help gather from under a blanket of golden leaves. These beautiful native trees are hardy in U.S. Department of Agriculture plant hardiness zones 4 through 9. You can propagate black walnut trees by transplanting seedlings growing under a mature tree to a site where they will have the space they need to thrive. This can be a learning activity for children, but great care is needed to avoid damaging the long taproot.
Excavating the Taproot
Water the ground thoroughly around the walnut seedling the day before you plan to move it, if the soil is not already moist.
Slice vertically through the top layer of soil to a depth of 6 or 8 inches, forming a ring about 6 inches from the trunk of the young tree. Do not pry upward with the shovel or remove any soil at this point.
Continue to loosen and remove soil from around the upper lateral roots with a trowel, being careful not to damage the vertical taproot. The goal is to remove all the soil in a 6-inch radius around the taproot to depth of at least 6 inches.
Fill the hole with water, and allow it to percolate before slicing further into the soil.
Slice vertically with the spade shovel into the soil in a ring around the taproot at the bottom of the hole. Form a complete ring by slicing into the soil, but do not remove any more soil at this time.
Gently begin to pry up on the taproot with the shovel from all sides. Pry a little bit at a time on all sides of the hole until the taproot is free.
Dig a hole in the new location to the depth of the excavated taproot, and as wide as the spread of any lateral roots.
Hold the seedling in the center of the hole so that the crown of the roots is even with the surrounding soil level and begin to backfill the soil into the hole. Be sure to break up any heavy clods of soil in the process. Carefully tamp the soil around the roots by hand to eliminate air pockets.
Apply a 1-inch layer of compost over the root zone, and cover with 1 to 2 inches of mulch to protect the soil. Water thoroughly.