Rhododendrons and azaleas grow best in light, well-drained soils with good soil aeration and an ample supply of soil moisture during the summer. They can be grown in heavy soils if special precautions are taken.
Rhododendrons require an acidic soil, ideally with a pH between 5.0 and 5.5. Alluvial or river-bottom soils are often more alkaline, and must be enhanced with fertilizer to increase acidity. Soils too acidic can be made more alkaline by adding ground limestone. Rhododendrons have shallow, delicate roots susceptible to rot. Good soil drainage is essential to the health of the plant.