What Does Dawn Dish Soap Do For Your Plants?

Anyone who's ever done a quick Google search after discovering dreaded aphids clustering on their plants may have seen Dawn dish soap pop up as a suggested home remedy. In fact, the internet is full of guides for homemade pest sprays that are made with diluted blue or green Dawn dish soap. But the question is not only about how effective this is, but what does it actually do to plants? 

Like many of these hacks, there's some science behind it. In short, using dish detergent can actually kill soft-bodied pests, such as aphids, thrips, and spider mites, and so it can be a tempting and easy solution to get rid of bugs on indoor plants as well as those growing outside. That said, it's a contact-based solution, which means the spray needs to directly hit the pests to kill them. Once it dries, the soapy spray stops working.

As for what Dawn dish soap does to the plant itself, it may not be the best thing for them. As a detergent, Dawn is built to break down oils and grease, which is great for our plates and surfaces, but on plants, it can damage the protective waxy coating on their leaves. And while this risk isn't necessarily the same for every plant — as the concentration of the detergent, the species of plant, the weather, and whether the plant is already stressed can all have an influence — it isn't exactly a spa day for your greenery.

So, while spraying a solution made with Dawn dishwashing liquid can be effective on some insects, such as aphids (if direct contact is made), that same mixture can result in harming your plants in a different way. Further, because the spray is contact-based, you'll find many experts conclude that the homemade solution's effectiveness is not only limited (since insects can escape it by arriving after it's been sprayed) but also highly variable.

Given this, there may be better ways to manage your plants and their pests. For example, simply checking your plants regularly for pests is not only considered good plant care, but it can help you catch an infestation while it's still manageable. For more established infestations, meanwhile, this may require a dedicated treatment. Most horticultural experts recommend using insecticidal soap that's been specifically formulated and labeled for use on plants rather than any household dish detergent, such as Dawn.

Sure, using a Dawn-based spray may knock out some pests on contact and rid your pest problem quickly. However, whether it is worth potentially damaging the plants you're trying to protect in the process is a judgment for you to make.