Answer: Cleyera prefer acidic soils so I wonder if the concrete foundation is leaching, making the soil too alkaline? You might want to test the soil (test kits are available in garden centers). Cleyera prefers a soil pH of 4 to 6.5. They also grow best in dappled to part sun. If they are receiving all day sunshine, they may be cooking, especially if there is reflected heat from the side of your house. Hope this information helps you determine just why your Cleyera are declining.
Best wishes with your landscape!
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