It's important to care for your new tree from the day you plant it. Using a rototiller is one way to make the process of planting the tree easier and to make the surrounding soil healthier. Not only does a rototiller serve to help in amending the soil around your new planting, it can also be used to dig a hole for the new tree.
Till the area where you wish to plant the tree as well as 6 inches around it. Dig the tines into the soil to a depth of 8 inches. Set the rototiller's depth gauge, if available on your model. Work in rows until soil is loose.
Remove all rocks and weeds from the soil by hand. Toss weeds into an outdoor trash container. Place the rocks in another area of your yard or garden to increase drainage.
Shovel a 2-inch layer of compost or a mixture of 1/2 compost and 1/2 peat moss on top of the soil. Retill the area to incorporate amendments into the soil.
Set the tiller where you choose to plant the tree. Start tilling and work to the depth of the tree's root ball, usually about 12 inches.
Till the width of the hole three times wider than the diameter of the root ball. If after tilling to the depth of the root ball, the hole does not appear wide enough, set the tiller on one of the hole's side and retill to the hole's depth. Continue tilling a different side of the hole each time, working in a circle, until you have a hole wide enough for planting.