If you soak the ground the day before, really well, it will be that much easier to dig up a young tree or bush that you want to move to a different area of the garden.
I wish we had thought of that before we moved my daughter's crepe myrtles last summer. They seemed to have survived the move, but man! were they tough to dig out. We may have been lucky they lived... or we might find out this year that they didn't.
May all your weeds be wildflowers. ~Author Unknown
Glad this was of some help. I know I found out the hard way about doing this.
I now wait until the tree/shrub is dormant, which is usually very late winter/early spring. I have not lost a single one doing it this way.