While Revit has adequate tools for individual plants, planting areas (for perennials and the like) are not as easily done. There are many system families that calculate areas: filled regions, floors, rooms, and areas. Though you could use filled regions, it is never advisable to use an annotation for a physical (model) element. Instead, I recommend areas.
Areas are funny little families. Like rooms, they overlay over everything and only appear in plan view. Since they are designed for floor plans, they are not ideal for planting plans, but they work well enough. Just like most things in Revit, this process requires a bit of investment initially, but the payoffs are there immediately when you start tagging.
