Calculate how large an area around the roots you will need to dig out. Measure the trunk of the tree and add 12 inches of area for each inch of trunk diameter. A willow tree with a 2-inch trunk will require a 24-inch hole.
Prune the roots three months before transplanting. Drive a sharp shovel into the soil at the edge of the determined root ball diameter to sever the roots, continue pruning the roots all around the base of the tree. Prune the roots in the fall for winter for spring transplanting.
Soak the soil around the weeping willow tree three days before transplanting. Dig out the rootball. Drive the shovel into the soil 6 inches outside of the root pruning circle. Work the shovel all around the root ball. Make the hole half again as deep as the planting hole is wide.
Lift the rootball out of the hole by pulling back on the shovel and working it free. Lift the tree onto a piece of burlap at the edge of the hole. Wrap the burlap around the rootball and tie it closed to keep the soil from falling away from the roots.
Lift the tree from under the rootball rather than by the base of the trunk and place it on a hand truck or in a wheelbarrow.
Prepare the planting hole at the new site. Weeping willow trees grow best in an area that gets full sun, though it will tolerate some light shade. Create a planting hole that is half again as large and as deep as the root ball.
Unwrap the root ball and carefully place it into the hole at the prepared site. Push the soil back into the hole around the root system. Press down firmly as you go to to press out air holes. Water the soil until it is damp to the bottom of the hole. This will settle the roots in their new environment.
Check the moisture level of the soil every few days after transplanting. When the top 2 to 3 inches feel dry to the touch, soak the area around the weeping willow tree.