Please Note-Rhododendrons require soil that has a high acid content. A pH of 4.0 to 5.5 is recommended. When planting we suggest spreading 1/2 lb. of fast acting Aluminum Sulphate around each plant, working it throughly into the soil. To maintain the proper pH a top dressing of 1 cup Soil Sulphur worked into the soil every 3 to 4 years is sufficient.