Soap-Based Herbicides

Soap-based herbicides can be effective on weeds.

The active ingredient in soap-based herbicides is potassium salts from fatty acids. The soaps work as a post-emergence weed control in flower and vegetable gardens.

Function

Herbicidal soaps penetrate a plants' waxy cuticle and dry out the plant. They kill only the parts of the plant that they come in contact with.

Uses

You can use herbicidal soaps to control annual weeds, as well as moss and algae. Because roots are not affected by the soaps, they are less effective on perennial plants. Apply the soap in the spring when plants are growing rapidly.

Considerations

Herbicidal soaps have low toxicity and are biodegradable. However, when spraying, shield plants to keep them from coming in contact with the herbicidal soap, because it is not selective. These soaps may not be as effective on older weeds.

References

• Clemson University Cooperative Extension; Glyphosate Damage on Tomatoes; J. McLeod Scott, et al.; July 2010
• Oregon State University Extension Service: Least Toxic and Organic Pesticides for Gardeners
• Montana State University: Herbicidal Soaps, a Less Toxic Option
• Washington State University Extension: Chemical Weed Control for Home Grounds