Minecraft wiki entry for Pumpkin_and_melon_farming, associated text: For each jungle chunk generated a random point is chosen and 64 attempts are made to find a random replaceable block (e.g. air, long grass, or vines) with grass beneath in a 15×15×7 region around the point in which to place a melon. Note the random point could be far in the air or far underground, greatly reducing the chances of melons being able to be placed.