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.
While many of Revit’s site tools can be disappointingly limited (or even nonexistent), planting plans are one of the things that make the program worthwhile.
Planting plans can get very intensive, so I’ve broken them down into three levels of complexity, starting with the most basic, which can be done with standard, out-of-the-box Revit.
The most basic planting plan is done by placing individual plants, tagging, and scheduling them. The default Revit plant famillies are RPC. I have heard some complaints about this, since some people prefer actual 3D trees, but from my experience 3D trees bog programs down quickly, so I am quite fine with them and we use RPC plants for all our individual plants.
This is what the default red ash looks like, in realistic and ray trace mode.