My friend, the Flaneur du Pays, is an architect and claims to be more of a vicarious gardener than a knees in the dirt type, but he has a lot to say about cachepots, jardinaires, urns and plain old pots. He will be guest posting from his cottage moderne set amid a grove of trees, in sight of  a salt marsh and Long Island Sound, for a couple of days while I put my knees in the dirt.…