Herbicides for Roofs

Written by catherine duffy
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Herbicides for Roofs
Debris filled surfaces give life to unwanted roof gardens. (old roof image by AGITA LEIMANE from Fotolia.com)

Even the most ardent flower and lawn lovers do not want vegetation to flourish overhead. Plant growth damages roofs and limits their lifespans. Roofs in wet climates host moss and algae. Drier climates and older roofs may yield grass, dandelions and other weeds. Identify the flora growing on your roof. The best type of herbicide remediation is dependent upon the type of vegetative growth you find.


Glyphosate is one of the active ingredients of popular, over the counter herbicides such as Round-up. Cornell University's Extension Toxicology Network considers the chemical a "moderately toxic herbicide." Chemical run off from the roof will not injure animals but, since glyphosate is a systemic herbicide, it can potentially harm your garden or lawn. Follow the directions on the label when using any chemicals.

Unfortunately, glyphosate does not remove moss or algae effectively. It will kill off initial growth but algae and moss will return, especially if provided with optimal growing conditions. The best way to remove moss and algae is by cleaning debris from the roof. This eliminates the mosses' growing medium. Moss and algae thrive in shade so the removal of overhanging tree limbs will help minimise moss and algae growth.

Sulphate Compounds

Oregon State University horticulturists suggest the use of copper sulphate to diminish the growth of moss in lawns. A similar compound, Ferrous sulphate is also used. If these chemicals are used on a roof, be aware that they can damage metal surfaces. Since metal roof surfaces are not optimal for root development roof herbage should not be an issue. Consider installing a metal roof if you would like to significantly decrease the possibility of overhead vegetation.

Copper sulphate and Ferrous sulphate compounds can stain cement and concrete so beware of any runoff near cement work. Copper sulphate and ferrous sulphate do not harm the environment. Sulphates help plant growth so this is not a good solution for roofs covered with weeds or grass.

Zinc Sulfate

Commercial moss control substances contain zinc sulphates which are potentially hazardous when introduced to groundwater, humans and animals. The Northwest Coalition for Alternatives to Pesticides suggests the installation of zinc strips. These three-inch metal strips are nailed near the peak of slanted roofs. As rain washes down the strips the remainder of the roof is rendered inhospitable to moss and algae. This is considered a good alternative to spraying the roof with sinc sulphate solutions.

Herbicides for Roofs
Peaked roofs outfitted with zinc strips are inhospitable to mosses. (Roof image by Mohd Haka Khambali from Fotolia.com)

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