hibiscus bushes against fence
I have a row of hibiscus bushes against a fence. A few are doing well, others terribly. Why? All have been in the ground for quite awhile but there is a major difference in how they are doing. All are watered the same amount. Planted in front of a fence, the plants face west. Some of the plants' leaves never get large. Others do ok and then drop most of their leaves, then start growing them again. The ones on the left of the photo look terrific at all times. Can't figure out why some should do so well while others struggle.
I would inspect the plants carefully for signs of insects.
The warm dry temperatures are the perfect conditions for insects to attack the hibiscus.
Also take a look at your watering practices. Hibiscus need water daily during there growing season, and may need twice daily water if the temperatures and above 85 degrees.
Here are several links that should help you to pinpoint the issues.
Neem Oil is a good treatment as it works as both an insecticide and fungicide.