I guess you could double auger and fine tune with a shovel. The nursery is wrong about the hole size.
Standard is two times the width of the root ball, but no deeper than the rootball. Because clay doesn't drain very well you can even go wider and I recommend scarating the sides of the walls and tapering them too. Some-times you even have to dig drainage canals in the clay.
We can't use Birches up here with much luck lately. There is a beetle called the bronze birch borer that is devastating many of ours.
Preventing drought stress helps to control this problem.
Last edited by Dr.NewEarth; 04-11-2012 at 12:10 AM.
Reason: GO CANUCKS GO