The wilting may be due to a fungal infection in the soil. The fungus enters the roots and into the plants stems then into the leaves. The wilting is a sign of stress. There are several causes of stress such as too much water or not enough, and poorly drained or compacted soil. You need to tackle the problem as soon as the wilting starts. If the plant is in full sun then the heat places the fungi infected plant under more stress. Place some shade over the plant such as an old umbrella for a start or, if possible, remove the plant and place it into the shade. Pick off the yellow leaves so that the plant does not waste energy in causing them to drop off. Leave the green wilting leaves alone. Treat the plant with an appropriate fungicide. If you leave the plant in the ground you might consider using worm casting. You could call a garden club that has hibiscus enthusiasts to seek advice.

- Stephen Young