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I live in Portland, Oregon and I'm battling moss on my asphalt shingle roof. I usually scrub it off manually, but it's extra bad this year and I might need more help than my broom.

My neighbor swears by Moss B Ware which is zinc sulfate. I don't know anything about this chemical and before I sprinkle it all over my roof, I want to understand just how toxic and/or creepy it is. I only use organic products in my garden. Is it responsible to use this chemical on my roof/yard? If not, can you recommend something better?

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  • Is the roof flat or pent (sloping)? – Bamboo Nov 10 '20 at 19:32
  • The material safety data sheet doesn't say much, it appears dust is the most hazardous thing if you breath it in a lot..pure-chemical.com/msds/Zinc%20sulfate.pdf – kevinsky Nov 10 '20 at 23:15
  • The roof is pitched but gentle. I can walk in it easily. – emersonthis Nov 13 '20 at 15:25
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A quick google search on Zinc Sulfate yielded this interesting page.

Briefly, it's fairly innocuous in an of itself, but like many inorganic salts, too much can have environmental effects. If you have runoff into waterways, it's toxic to aquatic fauna. I don't know how much you have to use to control moss. Use according to label and you're probably okay.

From the website:

What happens to zinc sulfate in the environment? Zinc naturally occurs in the environment. It can be found in animals, plants, and soil. Zinc may come from natural sources, pesticides, or human activities such as farming, and the production of batteries, animal feed, and metals. Zinc is also used as a food additive.

Zinc sulfate is an inorganic salt that dissolves in water to form zinc ions. The formation of zinc ions depends on water pH and the presence of agents that can bind and capture zinc. Solubility makes zinc available to plants and other organisms in soil; that availability depends on soil pH. Zinc in the environment is considered immobile because different substances bind to it.

Can zinc sulfate affect birds, fish, or other wildlife? Zinc salts are slightly toxic or practically non-toxic to birds and highly toxic to freshwater fish and invertebrates. No data were available on toxicity to bees. Bees and other pollinators are not likely to be harmed because they do not eat much plant material.

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    I found that fact sheet, too. But I found it frustratingly inconclusive. I was hoping there might be consensus from responsible gardeners about whether it's responsible to use this product on a roof. Does it contaminate ground water? Will it kill other plants or insects in my yard? I never use products like Round-Up to kill weeds. Is this in that category? – emersonthis Nov 10 '20 at 17:17
  • Not in the same category as glyphosate, an organic compound. Think of zinc sulfate like you would table salt. A little bit is fine, even necessary. Too much can cause problems. I seriously doubt it would harm any plants or insects in your yard, used according to label. I don't know enough about it to comment on the groundwater question. – DCookie Nov 11 '20 at 17:49

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