What kills moss on a roof best?

What kills moss on a roof best are products containing zinc sulfate, potassium salts of fatty acids, or copper that are specifically formulated for asphalt shingles and kill moss without damaging granules. Among the most effective, zinc sulfate monohydrate, found in products like Moss B Ware and Moss Out for Roofs, is considered highly effective as it desiccates moss and prevents regrowth, especially when applied as a powder on a dry day and allowed to be washed by rain. Potassium salts of fatty acids, found in products like Bayer Advanced Moss Killer and Safer Brand Moss Killer, work by penetrating moss and killing it quickly and are considered environmentally friendly and shingle-safe. Commercial ready-to-spray products like Spray and Forget and Wet and Forget Outdoor are also very effective, as they kill moss, algae, and lichen gradually without scrubbing or pressure washing, using a no-rinse formula that works over weeks. For best results, apply moss killer in late spring or early fall when moss is actively growing and rain is expected within a few days to help activate and wash the product. Avoid using chlorine bleach, which can damage shingles and corrode flashing, and never pressure wash moss, which strips granules. After moss dies and turns brown, gently sweep dead moss off with a soft broom from ridge downward. Installing zinc or copper strips near the ridge provides long-term prevention after killing existing moss.