Rose of Sharon, also known as hibiscus syriacus, is, as its botanical name suggests, not a rose at all but a relation of the hibiscus that sports foliage reminiscent of maple leaves and belongs to the mallow plant family. Rose of Sharon is a summer and fall blooming shrub that is hardy in USDA Zones 5 through 8 and will continue to bloom into winter when grown in warmer climates.
Feed your rose of Sharon in September or October with a good quality balanced water soluble fertilizer. Apply according to the package directions around the root ball and drip line of the shrub. Keep fertilizer away from the immediate area surrounding the trunk, allowing at least a five inch perimeter which will encourage healthy outward root growth and prevent damage to the trunk. Feed again in the spring when the last frost has passed and the ground soil has thawed.
Water in the fertilizer deeply and slowly around the base of the plant allowing the water to percolate the fertilizer down into the soil. Keep the soil evenly and lightly moist with weekly watering through the fall.
Mulch around the base of your rose of Sharon with a one or two inch thick layer of good quality compost. Pull the compost out a few inches from the trunk to prevent rot and continue it out to a few inches past the drip line. Mulch will hold moisture in and protect the roots from cold winter temperatures.