I thought the auger would be perfect, don't do it. All of the 100 bare root Black Walnuts in clay soil were totally root bound in clay pots from the auger smearing. The ones done by hand thrived.
That's why I mentioned what I did - 1,2,3. An auger will glaze the hole such that you've created a non draining pot in the ground with certain death to the tree. That hole must be fractured. Some go to the extreme of taking their auger bit to a welder and have him weld "bits" or sharp "nipples" along the spiral so that it scarify's the sides and bottom.
One of the best, most used, and least expensive tools on the farm. Knife blade, chisel foot. This thing has fractured miles of clay. Helps to have a 4WD tractor too regarding wheel spin.
