This tip might be helpful. I also have had several double Hibiscus in pots, and mine often have the bud drop problem. The last one I bought is about 2 weeks old, and it has dropped 4 or 5 buds. Here's something I've learned from researching this problem. Hibiscus hates any environmental change, so just relocating it from a nursery to your patio causes stress. Repotting also causes stress. But the biggest thing is this: Do NOT turn your hibiscus pot while it is in bud! We often want to turn our pots so that the plant grows more evenly on all sides, but you cannot do this to a Hibiscus in bud. If you do, the buds will fall off. Probably has to do with the heavy bud being forced to grow in a different direction toward the sun; this bends the bud stem, and off comes the bud! Wait to turn your Hibiscus plant until there are no, or only a few, very small buds. If you must turn it or move it while the buds are large, turn it no more than 1/4 turn each day. You rarely read about this tip, but it's SO important with double Hibiscus. Good luck with yours!