Spring (March through May) is the most popular time in Rock Hill because it clears the winter grime and pollen buildup before summer humidity accelerates algae growth. Fall (September through October) is the second most popular window — cleaning before winter prevents mold from sitting on surfaces all season. That said, house washing can be done year-round in Rock Hill’s mild climate. If your home shows visible algae or mold streaks, that’s the right time regardless of season.