A bluegrass lawn at six thousand feet spends all winter pressed flat under snow and wind, and come April it needs air more than it needs anything else. Castle Rock Aeration and Power Raking Ltd. does precisely what the name says — cores pulled and left to crumble back into the ground, thatch raked out, the whole yard opened up so water and root can find each other again. Around Diamond Ridge and the Woodlands the difference shows three weeks later, in a green that goes deeper instead of merely wider. When the cold comes the same trucks push snow off drives and clear the walks. Two ends of the calendar, one idea: take care of the ground and it takes care of the house.