Last year I (by myself!!) built a waist high raised bed. I didn't have enough soil, so I placed flakes of straw and old hay in the bottom and then topped it off with 14" of three year old horse manure and a little topsoil. I planted strawberries and asparagus and they did GREAT! Problem is, here at the end of the season, the straw broke down and the bed has sunk in. Being new at this, I knew it would sink, but it didn't occur to me that perennial plants would not be a good choice here. When the strawberries get brown I don't mind pulling them up and either putting them somewhere else, or putting in a "new"batch of 3 y/o horse manure and putting them back in.
1) Is it okay to do the same thing with the asparagus when they turn brown?
2) Since both strawberries and asparagus are harvested in the spring it seems like I am not using the waist high bed to my best advantage. Is there something else I could put in there that is harvested in the summer?
When I put in my asparagus bed, I dug down 2' and put in maybe a foot of rich soil, then planted the asparagus crowns in that. I have gradually filled it to ground level or above, and the asparagus still comes up strong. That said, I do tend to think that asparagus is not the best occupant for a raised bed, at least such a tall one. It might not be happy over winter being so exposed to cold (depending on your climate).