No worries your Rose of Sharon hibiscus will do just fine if you follow the instructions on the Osmocote fertilizer and sprinkle the product on top of the soil around the base of the plant. Then work the granules into the top one to two inches of soil. Use your gloved fingers or a light raking action and the roots will be fine.  As the weather heats up the fertilizer will be released when the shrub is growing and needs feeding the most. You can add a mulch over the product to keep down weeds and conserve moisture but it is not necessary to put fresh soil on top of the Osmocote if you work it gently into the soil. Keep growing, Marianne Binetti