Ferrous sulfate treats lawns for moss.

Why Use Ferrous Sulfate on Lawns?

by Sarah Moore

Mosses, though pretty in some garden settings, can act as an irritating weed in others. Lawns are such a place, where the presence of moss destroys the uniform green of grass with a darker, scrubby presence. Moss does not actually kill lawns, but if you don’t want it there, you can apply ferrous sulfate to get rid of it.

1. Indications of Ferrous Sulfate

Ferrous sulfate kills moss without harming the grass around it. In fact, iron substances oftentimes improve the look of lawns by deepening the green color of grass. Although ferrous sulfate is effective at killing moss, it is not a permanent solution. While most people assume that moss on the lawn means that it is killing the lawn, this is not true: moss is an opportunist that moves in where lawns have failed. Therefore, applying ferrous sulfate will help initially rid your lawn of moss, but you must then act to improve lawn health.

2. Application of Ferrous Sulfate

Add 3 ounces of ferrous sulfate to 5 gallons of water, then apply to the lawn with a sprayer. Five gallons of ferrous sulfate mixture should provide moss treatment for about 1,000 square feet of lawn. Because it doesn’t harm grass, you can safely apply ferrous sulfate directly on lawn areas that are affected by moss without worrying about it touching the grass. Do not apply iron when temperatures are higher than 80 degrees Fahrenheit or when grass is already wet, and water the lawn afterward, otherwise turf burn may result.

3. Moss and Lawns

Moss is a poor competitor with healthy grass, and will almost never appear on lawns that are healthy and actively growing. Although applying ferrous sulfate will help to keep moss out of lawns, a better bet is to figure out why your lawn isn’t performing well and fix the problem. Always choose grasses suited to your landscape conditions -- sun or shade, soil type, moisture levels -- and climate -- cool-season grasses for cool areas or winter, warm-season grasses for warm areas or summer. A well-functioning lawn is the best moss buffer there is.

4. Iron Toxicity

Although ingesting ferrous sulfate will not usually have fatal results, it can have very serious effects, especially in children under the age of five. Children who’ve ingested iron may exhibit symptoms of iron poisoning ranging from vomiting, diarrhea and stomach pain to more serious intestinal damage. Untreated iron poisoning can result in coma within 48 hours, and in gastric scarring within several weeks. If you suspect a person or animal may have ingested iron, seek professional help immediately.

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