By two o'clock in July the sky west of Riviera Beach stacks up dark, and anyone who works outdoors here learns to watch it. F.L INTEGRITY LANDSCAPING plans the day around that anvil of cloud — hedges squared and driveways cleared of clippings before the first fat drops come across from the Glades. Growth is relentless in the wet months; a ficus hedge left three weeks will swallow a window whole. So the mowing, the shaping, the trimming and the haul-off all run on a rhythm the rain sets rather than one a calendar invents. Yards through Riviera Beach, Riviera Beach Heights and the blocks toward Palm Beach Gardens stay in shape because somebody keeps that pace.