What roof moss killer is safe for asphalt shingles?
Short answer. Look for a moss killer labeled for use on asphalt shingle roofs, typically products based on zinc sulfate, potassium salts of fatty acids, or quaternary ammonium compounds, or use a diluted bleach solution as shingle makers describe for algae. Apply it on a dry day with a low-pressure sprayer, follow the label exactly, protect plants, and let the moss die and loosen before removing it gently.
Common types
- Zinc sulfate products: powders or liquids that kill moss and leave some lingering protection. They can stain some surfaces and harm plants, so keep them off painted trim and rinse plants nearby.
- Fatty acid soaps (potassium salts of fatty acids): fast acting and comparatively gentle, but with less lasting effect.
- Quaternary ammonium products: the spray-and-leave type. They work slowly over weeks as rain helps break down the dead moss.
- Diluted bleach: kills algae and surface moss quickly, but is harsh on plants and needs careful rinsing.
How to apply safely
- Read the label. Pesticide labels carry the legal use directions, including roof suitability and rates.
- Pick a dry day with no rain in the forecast for the time the label specifies.
- Wet and cover plants below, and plug or redirect downspouts if the label warns about runoff.
- Spray with low pressure from a ladder or the roof edge; avoid walking on treated, slippery shingles.
- Wait for the moss to brown and loosen.
- Remove dead clumps gently, working downhill with a soft brush or plastic scraper, or let rain wash them off.
What to avoid
- Pressure washers and stiff wire brushes, which strip granules.
- Products not labeled for roofs, or chemicals your shingle maker does not approve.
- Scraping off live moss, which pulls granules with it.
Prevention
Trim trees for sun and airflow, keep gutters and valleys clear, and install zinc or copper strips near the ridge. Algae resistant shingles help at replacement time.
See moss and lichen on roofs and black streaks and algae on roofs.