I heard that a lot of grocery stores poor bleach and etc. on top of food they put in the dumpster, to keep people from eating it. Sad, but it will protect the store from a law suit, if someone eats the food and becomes ill because it's spoiled, and then tries to sue.
Re the plants, remember that if you ever DO score such mark downs, be sure to open the package and examine for mold, rot, or etc. Those plants were marked down for a reason, remember.