blooms not opening

I purchased three different hibiscus from Lowe's for my b-day (late July). Potted them in good sized pots for gallon plants. I keep watered regularly (never sopping, but never completely dry) and I get lots of buds. However, the buds don't always open. They get so far and then drop. This problem happens on the singles, but mostly on the doubles. Yesterday I went out and two buds that fell off of Estelle (double) are now they are opening on the ground!

What am I doing wrong? Please advise! Many thanks!

You actually may be doing nothing wrong. If you were over or under watering you would notice it in the general "look" of the plant (wilting/yellow leaves). My hibiscus plants with double blooms are more likely to have a higher percentage of bud drops. The consistent summer heat can also be a factor in a higher percentage of buds dropping.
If its a pest causing bud drop I would guess its most likely to be "thrips". Thrips are hard to spot with the eye but if you look at buds that do open you may see markings/spots/scratch marks/discoloration on the blooms. These are visual signs associated with thrips.
You can treat the plants and the soil they are growing in weekly for at least 3 weeks and see if that helps. You also want to treat the soil because thrips lay their eggs in the buds and the buds then fall into the soil where they can/may hatch.
A couple of products I have used before are Ortho Systematic Insect Killer and any product containing "neem oil". Usually you will notice fewer buds dropping over the three week treatment cycle.
I hope you find this information helpful

thanks. I will keep a look out for thrips - but really don't think that is it. The heat did seem to make a difference. Now that we are back in the 80's (unusually cool for DFW in Sept) I haven't had too many drop off.