Several years ago I planted vegetables in straw bales as an experiment, and had pretty decent results, and again the next year with potatoes planted in the remains of the bales. What I did NOT like was how much seed was still in the bales and sprouted. I fought them for 2-3 years.
Two years ago I cleared a large area, laid down cardboard, covered it with 6" of alfalfa from some bales I purchased locally, and covered it all with 6" of wood chips. I had 2 bales of alfalfa left over and just stuck them in the barn.
This year I took those 2 aged bales out of the barn and planted winter squash in them. I'm totally astonished at the growth. In the photos, it's hard to see there are actually 2 plants but one is an acorn squash and the other is spaghetti squash.
The acorn squash isn't doing well, but there must be a dozen or so spaghetti squash growing on the other plant!