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Will Boric Acid Kill the Lawn?

Boric acid is derived from boron, a naturally occurring element. Boric acid is toxic when ingested by humans and causes skin and lung irritation if touched or inhaled. Some plant fertilizers also contain boron, as do certain weed killers. While plants require small amounts of boron to grow normally, large amounts are toxic to plants. Boric acid is sometimes sprinkled on lawns to kill ants or other pests, but can damage grass.
  1. Chemical Composition

    • Boric acid is usually white in appearance, and may resemble salt or a white powder. Its chemical composition is H3BO3. A related product sodium borate (Na2B4O7.10H2) is also sold under the name Borax. It is used in insecticides, weed killers and detergents.

    Plant Interaction

    • Boric acid in high concentrations kills plants. The boric acid dries out the plant and interrupts photosynthesis, thereby preventing it from manufacturing nutrients.

    Application

    • If using boric acid to kill weeds, place the substance directly on the weeds and avoid the rest of the lawn. This ensures that the weeds are killed, while preventing the boron levels in your lawn from reaching a concentration that kills your grass. If you have a major insect infestation on your lawn, select a different insecticide.

    Concerns

    • Boric acid should only be placed on the weeds in your lawn during dry conditions. Rainfall washes away the boric acid where it can get into local aquifers or runoff into neighboring properties. Keep children and pets away from areas treated with boric acid, as it is harmful if ingested and causes skin irritation. Wear gloves when handling this material.