Hard water could be the source of the problem. High alkalinity is common in hard water, and rhododendrons like acid, quite the opposite of alkalinity. Have your water tested for its pH, and help the plants with fertilizer (get something specifically for acid-loving plants, such as rhodos and azaleas). Your comment about 鈥渁ny type of soil鈥 is a little suspect here, too, though. Rhodos like acidic soil, so you should test it, too. Peat moss will help to add acidity to the soil (and retain moisture) and aged manure (mixed in in the fall, or not at all!) will help, too. For more on these details and others, see above.
Hard water could be the source of the problem. High alkalinity is common in hard water, and rhododendrons like acid, quite the opposite of alkalinity. Have your water tested for its pH, and help the plants with fertilizer (get something specifically for acid-loving plants, such as rhodos and azaleas). Your comment about 鈥渁ny type of soil鈥 is a little suspect here, too, though. Rhodos like acidic soil, so you should test it, too. Peat moss will help to add acidity to the soil (and retain moisture) and aged manure (mixed in in the fall, or not at all!) will help, too. For more on these details and others, see above.