Question
I have multiple hibiscus plants in my backyard.  A couple of them are mammoth hibiscus.  These bloom beautifully but drop flowers after one day.  From what I understand this is normal - but unfortunate.
The others are about 6'-8' tall.  They sprout many many buds.  Unfortunately they drop almost all of them and very few end up blooming.  If half of them would bud the plant would probably have overweighted limbs.
Details - They are planted behind a waterfall and around my pool.  There is occasional splashing that gets some of the branches wet. The high chlorination doesn't help those branches that do get wet but this is very slight.  I have never done any type of fertilization.  This bed is mulched.  There don't appear to be any bugs.  They get plenty of midday/afternoon sun. My sprinklers run in the morning (~5 min) and the afternoon (~5 min).
They have done this for 2 years now.  I know it is about time to trim them back, but want to plan ahead for next season.
This is my first attempt to do landscaping. I would appreciate any help you can offer.

Answer
Hibiscus buds are very sensitive and if your plants are stressed the buds may fall off before opening. Some types of hibiscus, especially those with double flowers, are very sensitive in general.

Stress can occur when the plants are fertilized too little or too much, or is over or underwatered. Insects, such as thrips can also cause it.

Generally, water deeply and infrequently rather than frequently and shallowly. You are watering the wrong way. I recommend that you gradually change watering patter to a few times per week, but then give them a good long soaking. I do not recommend using sprinklers. Instead put soaker hoses (made from recycled bicycle tires are commonly found at walmart, home dept, etc and are not all that expensive). Set them to go on, and water for 30 minutes. Do this a few times per week.

If you have mulched well then it should be ok.

Fertilizer will not help stressed plants (it will make it worse) but fertilizing plants can aid in the overall health. Once you have corrected watering pattern, then I recommend that you fertilize once or twice at the begining of the active growing season with a handfull of 10-10-10 fertilizer per bush. Allow 2 months between each application.

You can test for thrips by observing what happens if you touch the stems. If it looks like a newly poured glass of coke (similar to the carbonation) it is the flying thrips that you see. Immediately buy an insecticide and treat.

Some plants are sensitive to chlorine (some rose bushes have problem with too much) and I can not rule it out. However, it may not have to be the culprit. You should try to change the environmental conditions such as watering before you go that route.