Outdoor bronze sculptures are vulnerable to biological growth like moss, algae, and lichen, which can damage their surface and patina over time. To effectively prevent this growth, regular maintenance is crucial. Start by cleaning the sculpture every 3-6 months using a soft brush and mild soap solution, avoiding harsh chemicals that might strip the protective patina. After cleaning, apply a high-quality microcrystalline wax specifically formulated for bronze, creating a barrier against moisture and organic growth.

For sculptures in particularly damp environments, consider installing them in areas with good air circulation and sunlight exposure. Some conservators recommend applying a dilute solution of benzalkonium chloride (a biocide) annually, though this should be done cautiously to avoid altering the bronze's appearance. Another effective preventive measure is the use of sacrificial anodes in water features to reduce electrolytic corrosion that can encourage biological growth.

For existing growth, never use pressure washers or metal tools. Instead, use wooden or plastic scrapers and specialized bronze cleaners. Professional conservators often use steam cleaning for stubborn biological growth without damaging the metal. Remember that some natural patination is desirable, so the goal is control rather than complete elimination of all biological activity. With these methods, your bronze sculptures can maintain their beauty for generations while preventing damaging biological colonization.