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Fertilize light but often. Hibiscus in active growth are heavy feeders, especially when planted in pots. Some growers fertilize every time they water, in which case they use a diluted, water-soluble fertilizer solution at less than full strength.

Apply fertilizers in the cooler hours of the day, and be sure to water well before applying any granular fertilizer. Be especially careful to keep the plants well-watered after using any granular fertilizer.

The prevailing opinion is that hibiscus do not need (nor want) high amounts of Phosphorus (P, the middle number), but they do demand high quantities of Potassium (K, the last number). Tropical hibiscus fertilizers have ratio numbers like 9-3-13, 10-4-12, and 12-4-18.

Granular fertilizers have the advantage of providing plants with a constant source of nutrients. But some, even those marked hibiscus fertilizer are prone to burn the roots of the plants, especially if the plant is potted and becomes too dry. Moreover, these fertilizers break down unevenly, depending on temperature. The hotter the temperatures, the faster the granular fertilizer breaks down (despite label assurances). Some growers place a layer of mulch over the granular fertilizer to slow its rate of break down during the hot summer months.

For large hibiscus in the ground, it is easier to keep them consistently fertilized by placing "tree stakes" around the shrub/tree during the early spring. Since stakes for hibiscus are not available, I use stakes designed for palm trees. I have found that these formulas generally match those of hibiscus fertilizers very closely.

Remember: Phosphorus buildup or pH unbalance account for some 95% of the cases of slow decline and eventual death in hibiscus. Phosphorus, the "P" in the N.P.K formula, affects bloom quality and quantity, but hibiscus only need a small amount, since hibiscus "store" phosphorus. Excessive phosphorus will bind up other minerals. The effect can prove toxic to the plant.