There are several types of fertilizers and soil additives that will help to lower he pH of the soil and make it more acidic. These are sold as Azalea, rhododendron and camellia plant foods.  Osmocote makes one that lasts for 6 months and is best applied in late spring or summer. It is called Osmocote for Roses, Rhododendrons, Azaleas and Camellias. lYou can also add used coffee grounds and mulch with old pine needles to slowly help to acidify the soil.  Peatmoss helps hold moisture as well as lower the pH and the Canadian Peat Moss association is sharing a video about  harvesting peat moss in an environmentally friendly way in case you want to gather more information about this controversial topic. Enjoy those blue berries, Keep growing, Marianne Binetti