Yesterday, I sprayed both the soil and the leaves of my hibiscus plants with Garret Juice and orange oil following the directions of 2 tbs./gallon for each in a hose sprayer.

Today, these two potted well-established healthy hibiscus had yellow leaves on them. Was it the spray that caused them to yellow and drop? There didn't appear to be any bugs on them before spraying. I spray with orange oil to protect them from bugs because our neighborhood is new and grasshoppers, and a lot of other bugs seem to be invading from the nearby fields that are being developed to build new houses.

What time of day did you spray them? I think you're supposed to spray early, early morning, or in the evening, so that the leaves don't get direct sun after being sprayed. Maybe that's what happened?