Answer: Without knowing how you water it's difficult to say, but when leaves brown around the edges in the southwest, the problem is often salt burn. This is common in our area with low rainfall, alkaline soil and water high in salts. Frequent, light "sprinklings" or short time spans with drip irrigation, allow salts to accumulate in the top layers of soil, where the roots are, which is bad news. Occasionally water deeply enough to "leach" or push salts well below the root zone.
Browning usually occurs on the old leaves first. This excess salt accumulates in the leaf edges, where it kills the tissue and the leaf dries out and turns brown. It's important to water deeply, slowly and usually infrequently. A similar thing might happen from fertilizer burn.
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