Spread a 3-inch-thick layer of heavy mulch around the base of the variegated sea hibiscus to keep the soil from drying out completely. Leave a 2-inch gap between the mulch layer and the base of the trunk to allow moisture to evaporate from the soil.
Water variegated sea hibiscuses regularly, year-round. Run water at the base of the shrub rather than spraying from above to prevent common problems such as bacterial leaf spot and gray mold. Withhold water during rainy weather to keep the roots healthy.
Decrease watering and inspect the growing site if the variegated sea hibiscus develops yellow leaves or foliage loss on the tips of the branches. Allow the top few inches of soil to dry out between waterings to correct the problem, or transplant the tree to a site with better drainage.
Feed variegated sea hibiscuses a high potassium fertilizer with an N-P-K (nitrogen, phosphorus, potassium) ratio of 10-5-25 or 17-5-24. Apply the fertilizer monthly from spring until late summer. Use it at half-strength to prevent root burn.
Feed the variegated sea hibiscus each year in spring once it establishes an extensive root system and reaches 10 feet tall. Apply the fertilizer at full strength and water it in. Avoid over-feeding mature trees because they will develop weak branches.
Inspect the variegated sea hibiscus once a month for signs of damage. Look for sticky discharge or brownish nodules on the stems, which indicates an aphid or scale insect infestation. Spray the shrub with horticultural oil to eliminate the pests.