PJM Rhodo leaves turning yellow/red
The leaves on my PJM rhododendron are turning yellow/red (see picture). I'm not sure what is causing this or what (if anything) I should do to about it. Advice would be greatly appreciated!
The shrub is about three years old. For the first couple of years, it was totally ignored. I transplanted it early this spring to a full sun location (8+ hours of sun per day). I pruned away all the dead branches after it finished flowering and have been giving it a good watering once or twice a week, depending on rain.
The new leaves that grew this year seem to be in good shape. They are still bright green and not at all wilted. Over the past couple weeks, next years flower buds have been growing and also look good and healthy. However, all the older leaves turn yellow, then red and fall off. Is this normal? What should I do?