Hardiness Zone: 9b
By jpear from Riverside, CA
Yes, fertilize and you should get more and bigger blooms. Be sure you don't over-fertilize or you will get lots of lush green leaves and no blooms.
Hibiscus are my favorites so I have had lots of experience with aphids/Hibiscus. I don't know if soapy water is safe to use, but I know that insecticidal soaps are safe for Hibiscus, but after you use the soap, it will take a while for the plant to recover from the "treatment". I use a water hose (or sprayer in the kitchen sink for house plants), and no soap. I turn the water on low force and wash the aphids off the bottom of each leaf. Once washed to the soil, they will not climb back up and the plant will not need time to recover from soap or chemicals, so the blooms will keep on coming.
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