Answer: Since neighbors seem to be having better luck, there must be something in particular about your yard or soil or cultural practices that is causing the problem. Some fairly common causes of yellowing and failure to thrive would be that the lawn has been limed and the pH is no longer appropriate for the acid loving rhododendrons; an acidifier has been overapplied to the planting area; soil is poorly drained and thus remains soggy; plants are over or underwatered; plants are planted too deeply, especially if planted in heavy soil and/or watered heavily; balled and burlapped plants have not had the wrappings removed prior to planting and the roots are now restricted (burlap and string today are often synthetic materials and do not rot away); using a variety that is not fully winter hardy in your area; watering with water that has beent hrough a softener system; and finally, there is the possibility that there is a pest or disease problem at work and it is carrying over in the soil or on mulch debris or coming in with the plants.
It can be difficult to diagnose the cause without looking at the foliage. You might want to take a sample and possibly photos of the plants to your county extension (526-6293) and see if they can make a specific determination as to what is causing the problem and what to do about it. I hope this helps you trouble shoot.
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