Blue hour over Vinegar Hill: the cobbles go violet, the bridge lights come on, and up on the terraces the planters want water. Greengage Urbanscape, Ltd. works this end of Brooklyn where green space is measured in square feet and lifted three stories off the ground, handling lawn maintenance, bed planting, pruning, mulching and end-of-season clearing. Wind up here is a real force, so everything gets tied, trimmed and tucked before they climb back down. A rooftop patch of turf kept even and soft is an unreasonable thing in a harbor city, which is exactly why it is worth doing. The ground-level gardens downstairs get the same hands.