Experts and BHG readers answer.
I'm confused by your term "heavy sandy soil" because heavy is usually associated with clay and light is usually associated with sand. This is important because peonies, as tough as they are, languish in lean, dry soil. If that's what you have, then you will either need to move the peonies to another spot or drastically amend the soil to make it richer in nutrients and water-holding capacity. Copious amounts of compost are your best bet.