The best fertilizers for hibiscus should have a balanced ratio or equivalent amounts of phosphorus, potassium and nitrogen. A fertilizer that reads 10-10-10 or 20-10-20 is a balanced fertilizer. These fertilizers can be either water-soluble or slow-release fertilizers.
Hibiscus plants do well when fertilized frequently but lightly. If you choose to use water-soluble fertilizer, make sure not to use too much or you will burn the roots of the plants. To avoid this, use water-soluble fertilizers at half strength. Fertilize every two weeks in spring and summer, and monthly during fall and winter. Four applications per year are effective when using slow-release fertilizers.