The man who plants a tree knows he may never enjoy its deepest shade. But he still gets much in return: above all, a length of perspective that can absorb success and failure with the same, dispassionate sense of their transience. You could ask no better mindset of a horseman. And, sure enough, a Thoroughbred could wish for no better environment than the farm that shares its site with--and owes its name to--the oldest arboreal nursery in Kentucky. True to its heritage, John Mayer presides over the mares and foals...