Abstract: A rotary tiller device for tilling around trees and other similar obstacles comprises a rotary tilling head with a plurality of tines extending slightly outwardly, downwardly and forwardly from a support which rotates around a vertical axis of the head. A central plate rests upon the ground and defines a tilling depth of the tines. A cover prevents the support from damaging the tree. A mounting system for mounting the unit on the belly of a yard tractor includes a pair of rails mounted in place of the removed belly mower and a hydraulic fluid reservoir tank which slides into position on the rails and defines a support for the tiller head. A linkage between the tank and the tiller head includes a six-bar lever system mounted upon a pivotal plate.