Will Laundry Detergent Kill Grass?

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Grass thrives under particular conditions, and seemingly harmless conditions can kill it. A substance such as washing powder, while safe for your clothes, can mean the end of your well-kept lawn. Whether you spill detergent accidentally or use it as an insecticide, use caution to prevent it from killing your grass.

Safety for Grass

Though soaps are not inherently harmful to grass, washing powder specifically contains ingredients that damage grass, though not necessarily kill it. When using washing powder as part of an insecticidal spray, dilute it heavily with water. The University of Rhode Island recommends a dilution of no more than 3 per cent washing powder, or slightly less than 2 tbsp of detergent for every quart of water.


According to the American Rhododendron Society, water is an effective insecticide without the damaging effects of washing powder. Water-stressed plants are often more susceptible to insect pests, and spider mites and aphids can be kept in check with regular watering. Water your lawn before trying other methods.

Preventing Damage

Water can also stop the damaging effects of washing powder. Just as soaking grass with water dissolves harmful salts, it also dilutes washing powder and disperses it in the area. Soak the grass with 1 gallon of water for every 1/2 cup of detergent you estimate you spilt. This produces a 3-percent dilution of detergent, which is safe for grass.

Killing Grass Naturally

If you want to kill grass, use salt instead of washing powder. Unlike washing powder, salt is sure to kill grass rather than damage it. Cover the unwanted grass with salt to dry it out and deprive it of nutrients. Whiteness in the soil is a sign the salt is working.