Replace a lot of the old soil with bagged soil containing manure and compost with complete with fertilizer.
Dig out a 16x16 hole and put the new dirt in the hole.
Do not know what killed the rose bush but it is still there unless you remove a lot of soil.
I would also take two inches of soil off of the whole bed and put mulch on top; I use Cocoa Bean Hulls as they also have a small fertilizing effect.
