Does Spraying Plants With Dawn Dish Soap Harm Them?

Even though Dawn dish soap touts itself as a gentle product, should you be using it in your garden or on houseplants as an insecticide? Generally, no; you shouldn't spray Dawn dish soap on your plants, as doing so will almost certainly damage them. Even diluting the product with water, as homemade recipes call for, doesn't make it safe to use on living plants. While spraying it on plants can work on ridding them of certain soft-bodied insects, the soap solution could also lead to phytotoxicity, or chemical damage to the plant. 

Dawn dish soap contains preservatives, solvents, surfactants, and antibacterial agents. Together, these ingredients enable Dawn to cut grease and remove oils stuck on dishes (or ducklings). When you spray it on a plant's leaves, however, those same ingredients can strip oils from the leaves and remove a leaf's protective waxy coating, also known as its cuticle. Consequences may include drying out the leaves or creating leaf burn, which generally starts as brown, brittle areas on the edges of a leaf. This dryness eventually engulfs the entire leaf. 

Spraying Dawn dish soap might also cause premature yellowing, stunt the growth of the plant, or create brown or white spots on the foliage. Because of these issues (and even though Dawn products often rank as the best dish detergent, according to customer reviews), you should not spray it on your plants.

While you can find sources online that support using Dawn dish soap as an insecticide, you'll find many more that advise against the remedy. For example, the University of California Integrated Pest Management (IPM) tells its master gardeners not to recommend homemade pesticides for several reasons, including the fact that "Most dish soaps are not naturally occurring substances nor are they biodegradable. They can contain detergents and degreasers that are harmful to groundwater and aquatic and soil organisms."

You can also learn from the experience of fellow home gardeners. One Reddit user, for example, shared in r/vegetablegardening a few years back what happened to their plants: "... I just made the very unfortunate mistake of spraying my balcony vegetable garden ... with a mixture of Dawn dish soap and water to get rid of aphids ... My beautiful healthy bell pepper plant lost 90% of its leaves in less than 24 hours."

Instead of Dawn dish soap (which, technically, is a detergent), you can use insecticidal soap that's specifically formulated for plants. These contact-based soaps often contain potassium hydroxide and fatty acids. Still, be aware, even though insecticidal soap is safe for plants, it could harm sensitive, dehydrated, stressed, and young plants, so be sure to carefully consider your plants' conditions before using it on them. Plants that are sensitive to insecticidal soap include sweet pea, plum, and gardenias.