Minecraft wiki entry for Lush_Caves, associated text: Lush caves generate underground at y-10 to y-50 height, usually in areas with forested biomes. Azalea trees generate on any empty space above a lush cave, with roots consisting of rooted dirt and hanging roots that generate down until reaching the lush cave. This is most common at the surface, but they can sometimes generate inside caves if there is enough room.