It is not necessary to grow asparagus in raised beds. They do appreciate good soil, some moisture and drainage - not heavy clay. I always mulch mine pretty heavily with chopped leaves in the fall. This prevents most weeds. I mulch around the stems before cutting them down. You don't want heavy mulch right on top because the new spears would have trouble pushing through. It is beautiful, pretty easy to grow, tasty and nutritious. Resist the urge to harvest any for the first couple years. You should not harvest any spears (ever) that are skinnier than a pencil.