Experience is what you gain while looking for something else.
Built a 18" high raised bed in greenhouse earlier in season, put in 6" of wood chips at bottom, provide by council to site. Filled balance with soil and compost.
Planted up, crops growing nicely. Then from the bowels of the bed came, mushrooms, toadstools and huge great fungi beasties, crops lifted out and dying.
Dug down and wood chips alive, not going to use wood chip again as bulking agent.
Digmore.