Answer: There are a number of problems that can beset rhododendrons and cause foliage and wilting problems (and death), but those planted in a heavy clay soil will be very susceptible to root problems due to the poor drainage. And, there are diseases which carry over in the soil and will affect the replacement plants. If it is a disease issue, it would be unwise to replant with rhododendrons again as they too will be affected. It is also possible that the location is just not suitable for rhododendrons and you should consider planting something else there. Based on your description, I would suggest you consult with your local county extension to obtain a specific diagnosis of the problem(s) and based on knowing that, decide how to proceed. I'm sorry about your plants.
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