Copper sulfate is often used on lawns to treat outbreaks of mold, moss, or the pests that feed on dying lawns. But could copper sulfate cause the death of a lawn itself? Advice can be mixed. On one hand, copper is a known essential nutrient for many types of plant life, including grass. On the other, copper can poison plants, insects, and animals in high doses.
Do the quantities required by herbicide or pesticide applications provide too much copper and lead to the decline of a lawn over time, or will this copper help your grass grow? Below you can learn when copper sulfate crosses the line from necessary nutrient to deadly poison.
Will Copper Sulfate Kill Grass?
Yes, at relatively low concentrations, copper sulfate can kill grass. For example, adding 1 oz of copper sulfate to 1 gallon of water and spraying it over an area of about 250 square feet can kill moss and algae while sparing a lawn. Add 3 ounces to a gallon of water and spray it over that same area and you could begin to see the effects of slow copper poisoning- lack of recovery after mowing, roots dying off, visual “rusting” or red-tinge on blades of grass. Too much copper in the soil is also difficult to correct.
What Does Copper Sulfate Do to a Lawn?
If you have a problem with mold, mildew, algae, or moss buildup in a lawn, using a weak spray of copper sulfate will quickly eliminate these problems. It doesn’t take much copper to kill these smaller plants or organisms. If necessary, more copper can be applied a month following the first application, if the desired results have not been seen.
Too much copper added to a lawn can take years to get rid of and the effects of copper poisoning may not show up for several weeks after the copper spray is applied. Feeding your lawn a small amount of copper, on the other hand, may increase thickness and growth rate.
Related Article: What Kills Grass?
Does Copper Sulfate Work as a Lawn Pesticide?
Does copper sulfate kill grass-destroying pests? Yes and no. Copper Sulfate is a “molluscicide”. This means that copper sulfate kills snails, slugs, mollusks, and other gastropod-type pests or lawn residents. While snails and slugs often won’t harm a lawn, they can be food for animals that do dig up lawns and cause holes and bare patches in turf. Reducing these populations can discourage shrews, mice, snakes, and squirrels from visiting your yard.
How Does Copper Sulfate Affect the Soil?
Copper sulfate will build up in the soil until it is taken up by a plant, another organism, or until it has leeched into the groundwater supply. High levels of copper will prevent seed germination, plant growth, and will kill soil microorganisms.
How Do You Reduce Copper In Lawn Soil?
If too much copper sulfate has been added to a lawn, it can take quite a bit of effort to correct. First, the easiest way to correct a minor excess copper problem is by liming the lawn, if the lawn’s pH is already lower than 7.5. This is a delicate line to walk as you don’t want the pH to become too high and inhibit plant growth more than the copper already is.
A higher pH will increase the amount of copper healthy soils high in clay and organic matter will keep, making it less available for plant uptake. Less copper will be absorbed over time and plant root growth should return to normal in 1 to 3 months after liming.
Beyond adjusting the pH of the soil, increasing the availability of nitrogen, iron, zinc, and phosphorous can also reduce the uptake of copper. These nutrients compete with copper when they are taken into the plant, giving the grass greater “choice” of nutrients that can help them survive in a high copper environment.
If the grass is healthy otherwise, mowing the lawn more frequently and bagging or raking up clippings can also help reduce copper in the grass and the soil. This combined with the other methods should make it so an excess of copper can be depleted in about 2 years.
Will Copper Sulfate Kill Grass and Weeds?
Yes, copper sulfate can kill or prevent the growth of grass and weeds in small quantities. If applied directly to plants or soil and not diluted at a rate of at least 1 gallon of water to 1 ounce of copper sulfate, copper sulfate can kill the plant life in that area within just a few weeks. Further, no other plants will be able to grow until the copper content of that soil is sufficiently diluted. Without intervention, this can take years if not decades.
Can Copper Sulfate Be Beneficial to a Lawn?
Does copper sulfate kill grass and have absolutely no desirable benefits? No. Copper is a necessary plant nutrient and copper sulfate makes an easy form of copper to dilute and deliver to plants. If used correctly, this copper can prevent some plant diseases as well as discourage pests, eliminate snail and slug populations, and prevent the growth of moss and algae.
Thank you for your article on using copper sulphate to kill moss / algae in my lawn ( more like a patch of grass with lots of bumps and bare patches).
I am a fairly active 72 year old lady who has no help. I will now try to aerate my grass, treat the algae and then over seed.
Hi Joan,
Sounds like you have a good plan. The aerating will definitely help. You may want to also try reducing the amount of water your lawn gets, as moss loves moist/wet soil. Just be careful not to give too little water so the grass doesn’t begin to struggle.
Good luck with your lawn & thank you for the comment.
Tom.