Answer: "Bud Drop" is a sign of stress. In this case, I think it is due to transplant 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. I would simply give the plant a few more weeks to become more established in your garden and it should be strong enough to open the flower buds it is developing.
Best wishes with your hibiscus!
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