Yellowing of oleander leaves is a common symptom that the plants are too dry. Get out your hose and flood the root zone of the plants with water, then wait an hour or two and do it again. If the water runs over the surface rather than soaking in, make a raised collar of soil around the base of the plants to help retain water. In California, yellowing of oleander leaves that begins at the tip and spreads inward is a sign of a bacterial disease called oleander leaf scorch.

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