Certified GKH Gardening Expert
If there are few or no flower buds, this could be a soil fertility issue. You may have excessive nitrogen in the soil or too little of another nutrient.
Hibiscus plants also prefer acid soil; you may want to get a soil test to see if it needs to be acidified.
It is also common for hibiscus buds to fall off without opening in times of environmental stress, such as high temperatures.