Question
Do you generally prefer potting soil or plant-specific soil like roses and azaleas in slightly acidic soil?

Answer
Hi Sally, for beans I'd want the pH around 6.5, but the soil on the poor side.  It should be loosened, but not overly improved or fertilized.  Rich soil produces spectacular plants but few beans.  You want beans, so the plant should be stressed a little for better production.  When loosening the soil, I'd add no more than 10-20% compost, chopped leaves or finely ground pine bark to help separate the soil.  Jim