Answer: Ten year old laurels should have deeply established roots and should not require frequent watering, even during the hottest months of the year. It sounds as though their roots have remained shallow all these years - perhaps there's a natural barrier, or perhaps it's because of root damage from moles and gophers. I think the problem is worth investigating further. I'd dig down adjacent to the row of laurels to inspect the drainage of the general area. You may find bedrock 8 -12" beneath the surface which could stop root growth. Or you may find large enough voids in the earth to affect the health of the roots of your laurels. Perhaps the plants were not removed from their nursery containers when planted - don't laugh, it happens! I'd also carefully examine the undersides of the yellowing leaves, the stems, and the main trunks of your plants. Look for insects, wounds, girdling, cankers, etc.
You might also try thinking back on any chemicals that might have been used in the yard. Some herbicides contain glyphosate which can damage broadleaf evergreens.
If nothing I've mentioned seems to fit the problem, you might take a sample of the affected foliage to your local Cooperative Extension office or Plant Problem Diagnosis Clinic for professional evaluation.
Best wishes with your landscape!
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