Come the first cool Saturday of October, downtown Harlem fills for the Oliver Hardy Festival and every lawn on the way in gets looked at twice. Landscape Wizard spends that stretch on the details — mowing, edging, bed work, hauling off the leaves that come down late here, sometimes not until November. Autumn in this part of Georgia arrives slowly, more a change of light than of temperature. That long shoulder season is the best window of the year for shaping a yard and letting the shape hold. A crisp border between mulch and grass is a small thing that changes the whole front of a house.