Rose of Sharon is a tough, old-fashioned flowering shrub — an upright, vase-shaped Hibiscus that opens large, trumpet-shaped flowers from midsummer clear through to frost, when most other shrubs have finished for the year. Individual blooms in white, pink, lavender, or blue-violet — often with a contrasting red throat — last only a day, but a mature plant carries so many buds in succession that it stays in flower for months. It's the national flower of South Korea, where it's known as mugunghwa.
It flowers on new wood, so prune hard in late winter or early spring — cutting stems back by about a third encourages a more compact shape and larger individual flowers. Otherwise it asks for very little: full sun to part shade, average garden soil, and drought tolerance once established, which is exactly why it has naturalized so widely outside cultivation. The straight species and older cultivars are prolific self-seeders, and deadheading spent flowers before they set seed is the single most effective way to keep a planting from spreading into nearby woodland edges and disturbed ground; several newer triploid cultivars ('Blue Chiffon', 'Diana') were bred to be sterile or nearly seedless.
Japanese beetles and aphids are the most common pests, but the shrub otherwise shrugs off heat, urban pollution, and poor soil better than almost any other flowering shrub.
Fungal leaf spot
Brown or purplish spots on the leaves, often ringed with a yellow halo, that spread and merge in warm, humid, or wet weather; heavily spotted leaves yellow and drop early.
Pick off spotted leaves and clear fallen debris to remove overwintering spores. Improve air circulation by thinning, and water at the base so foliage dries quickly. If it persists, apply a copper- or sulfur-based fungicide at the first sign.