Answer: I've had the same problem with hibiscus plants. They are picky about getting enough water, and they tend to dry out quickly in bright sun and warm temperatures. Your plants may need to be repotted into larger pots so they don't dry out too quickly. Another possible cause of the yellowing is spider mites, which form white webbing on the undersides of leaves and where the leaves attach to the stems. Mites can be held at bay by spraying with insecticidal soap or even soapy water (use soap not detergent). Routinely spraying the plants outside with a hose can knock off the mites before they cause much damage. I would also reduce fertilizing until the plants recover. You can prune the plants to improve their shape and promote bushier growth.
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