What is the best roof moss killer?
Short answer. The best roof moss killer for most asphalt shingle roofs is a product labeled for roofs that uses zinc compounds or potassium salts of fatty acids, applied on a dry day and left to work rather than scrubbed or pressure washed. Diluted bleach also kills moss but is harder on plants and metal, so it needs heavy rinsing and protection for landscaping.
The main active ingredients
- Zinc sulfate or zinc chloride: kills moss and leaves a residue that slows regrowth. Effective, but runoff can stain concrete, harm plants and react with some metals, so read the label about gutters and landscaping.
- Potassium salts of fatty acids: soap-based, fast acting and gentler on surroundings; kills on contact but may need a repeat application.
- Sodium hypochlorite (bleach) mixes: kill moss and algae quickly and lighten stains, but can burn plants and fade some materials; rinse thoroughly.
- Quaternary ammonium cleaners: found in some leave-on outdoor cleaners that work slowly with rain over weeks or months.
How to choose
Pick a product whose label names asphalt shingles, or your roof type, and follow that label exactly; with pesticides the label is the law. For light growth on a shaded slope, a leave-on product that works with rain is easiest and keeps you off the roof. For thick mats, a fast-acting product followed by gentle removal once the moss is dead works better.
What not to use
- Pressure washers, which strip granules and can void a shingle warranty.
- Wire brushes or scraping across shingle edges.
- Homemade mixes of unknown strength, or anything not labeled for the metal flashing and gutters it will run over.
Make the result last
Moss returns wherever shade and debris stay. Trim overhanging limbs, keep valleys clear, and consider zinc or copper strips near the ridge. See moss and lichen on roofs and pine needles and leaves on the roof for prevention.