Answer: English laurels thrive in full sunshine so I'd look towards the soil for the cause of the browning leaf margins. Salt burn from excess fertilizer can cause brown leaf margins; overwatering might also cause this problem. Since your plants are in containers, you may want to investigate just how hot the roots become during summer afternoons. It is surprising just how warm potting soil can become when a container is in full sunshine and setting on a deck, patio or sidewalk. Excessive heat may have stressed the roots of your plants.
If you think you overdosed with fertilizer, you can flush excessive amounts out of the soil. This won't change the damage on the affected leaves, but it will keep the other leaves from developing brown margins.
Hope this gives you some clues as to what may have caused the brown margins on your laurels.
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