Answer: Because you want to promote blooms, the best choice in fertilizers is one with high middle number. The first number represents nitrogen (for green, leafy growth), the second number is phosphorous (promoting blooms and strong stems), and the third number is potassium (helps root growth and works in conjunction with the other elements to strengthen stems and shoots). For a hibiscus I'd use the all-purpose Miracle-Gro which has a nitrogen-phosphorous-potassium ratio of 15-30-15. If your hibiscus is in a container, dilute the fertilizer to half-strength and apply every 3 weeks during the growing season. If your hibiscus is planted in the ground, use the fertilizer as recommended on the label.
Hope your hibiscus rewards you with lots of blooms this year!
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