Abstract: An improved powered lawn mower of the type comprising a longitudinally extending engine bed support frame, a transversely extending cutting reel and bed knife assembly carried by the frame, a transversely extending front roller carried by the frame and longitudinally spaced in front of the cutting reel, and a transversely extending lawn conditioning roller carried by the frame and spaced between the front roller and the cutting wheel. The improvements comprise a conditioning roller vertical adjustment means carried by the frame and operable to adjust the vertical height of the conditioning roller with respect to the grass and the pitch of the bed knife together with conditioning roller drive mechanism which is enclosed and pivotable upon vertical movement of the conditioning roller.