Use a spade to slice a circle in the ground around the tree that's as deep as the blade and 11 times the trunk's diameter. Outside this circle, dig a wide trench; keep digging until you stop encountering roots. Work the spade under the ball at a shallow angle until it's free. Carefully slide the burlap under the ball, grasp the fabric, and lift the tree out of its hole.
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Burlap (42x42 inches for 18-inch-diameter root ball)