This is a grafted pawpaw and part of its understory. It has been established for several years and we are looking forward in 2010 to seeing what happens when dwarf comfrey comes into contact with water celery. Both are dense and fast growing. Jonathan and I both think dwarf comfrey will "win."
We keep the water celery in check in part because our chicken pen is right next to the patch so it is easy to cut extra growth and feed it to our girls.
The aster is a dwarf variety. We'll see how it does when the slow tsunami of water celery and dwarf comfrey reach it. A full-sized aster would stand a much better chance.