If you're able to adapt it, be careful not to bore too deep. The soil under the root ball will eventually resettle and your tree will sink. Other than that, good idea for breaking up the ground around the tree. I planted 4 last year using a 12" bit to bore multiple holes in a 3x3 square...that worked fairly well but wasn't really much quicker than just digging it out to begin with. When I plant trees in my orchard, I usually dig a 3x3 foot hole about 2' deep, remove half the soil and replace it with a composted soil conditioner. Mix thoroughly with the remaining soil, refill the hole, then plant. About the only thing the auger did was break up the soil and make it a little easier to shovel out of the hole.