Bud Drop
Notice buds dropping excessively? "Bud Drop" is a sign of stress. It is occasionally a problem, especially with double-blooming varieties, during excessively hot weather. Some hibiscus cultivars are more sensitive to heat and seem to drop buds almost naturally under these conditions. Hibiscus grow best in daytime temperatures ranging between 75 and 85 degrees Fahrenheit.
Not all "bud drop" is caused by excessive heat. Any stressful condition can prompt the plant to drop its buds. In many cases the cause is one of the following: lack of water, too much water, wind, heavy rain, insects (especially: hibiscus midges or thrips) and/or an unbalanced feeding formula. Try moving the plant into a more shaded area and regulate the watering more closely.