HI Erika, there are several reasons why hibiscus drops buds but one of the most common is when the weather is too hot. Anything above 85 degrees can cause buds to drop. Another cause is dry soil. Hibiscus needs constantly moist soil - not wet, but moist. Surprisingly too much fertilizer can make plants drop buds so always follow instructions for fertilizer use. I use Osmocote on my potted hibiscus as this is a slow release food and unlikely to cause bud drop from over feeding.  Follow the dosage on the Osmocote  bottle as the right amount depends on the size of your pot and plant. Although it is possible that insects like mites can cause bud drop on hibiscus you did mention the plant had green foliage so I do not think insects are the problem. Cooler weather is on the way if you live in a hot climate so keep on watering and use Osmocote rather than a liquid plant food and I think you'll have a happy hibiscus soon. Keep growing, Marianne Binetti