I am sorry for this delayed reply to your gardening question. The spring rush has brought a deluge of questions and we are working hard to catch up!
It may be that your gardenias are suffering from drought, soggy wet soils, or a root rot. Try to keep the soil moderately moist but not too wet. Prune out any dead areas and if the dieback continues consider trying a fungicide drench for root rots.
Thanks for the question. Best wishes for a wonderful gardening season. Please stop in again soon!
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