Kill moss on roof

Asked September 23, 2017, 3:45 PM EDT

On September 22, Thursday, I cleaned off my roof and applied Moss out. It rained the day before but hasn't rained since. 1.) Will the product work this time of year? I plan to apply more in May of 2018. 2.) What is the best product to use? 3.) Is a spray on product better than a powder? Thanks very much. Larry

Clackamas County Oregon

3 Responses

Thanks for your moss control question. Could you do me a favor and look at the label of the product you used? If it is the "Moss Out" sold by Lilly Miller, the label says:

"USE PRECAUTIONS and RESTRICTIONS: MOSS-OUT is for use on lawn or turf only. Do not use MOSS-OUT to control moss on roofs, patios or other surfaces made of concrete, tile, brick, wood or painted surfaces as severe staining may occur upon contact. Since MOSS-OUT can cause corrosion to galvanized metal, apply only with a plastic sprinkling can or a plastic hose-end sprayer."

Before I can answer your questions, I need specific information about the product. Once we can figure that out, we can explore further. Thanks!


Thanks for the quick reply. The product I used is Moss Out for Roofs and Structures, dry formula. Active ingredient: Zinc sulfate monohydrate - 99% (equivalent to 36% zinc as metallic.)

Hope this helps.



Oh, good! So, in responding to your questions, insofar as possible I'm going to refer to the label specific to your product, since "the label is the law." You probably have it handy, but some of my answers will come from information that is provided by the manufacturer to the EPA, which licenses its sale.

1.) Will the product work this time of year? Yes; label says "prior to the time when fall rains begin." "Destroying existing moss is done most effectively during times when its growth is is most rapid and rain is not expected for several days."

1.a) Will the product work in May, 2018? Yes; label says "or in early spring."

2.) What is the best product to use? Since any moss control product's active ingredient is either zinc or zinc sulfate, that's largely a value judgment on the part of the homeowner. However, this article has some alternative ways to control moss that you might want to read further on, both by physical and chemical means.

3.) Is a spray on product better than a powder? I think I'll let you read the above article so you can compare several aspects of various chemical mechanisms, since, as is to be expected, they all have both positive and negative sides, and your environment may militate for one versus the other. And, who knows, you may decide that a zinc strip along your roof's peak is more effective in the long term, is more appealing than climbing up on your roof annually.

Hope this information is informative and helpful to you. Good luck!