There are a lot of DIY remedies for eliminating insect pests on plants, and one of the most common is spraying with a solution of dish washing liquid. Does dish “soap” work as well as insecticidal soap? It is as safe for your plants? The answer may surprise you!
There are a lot of do-it-yourself recipes for eliminating bugs on plants using dish soap. And Dawn dish washing liquid is often featured as the “must have” ingredient.
But this is not the safe or natural solution we’ve been led to believe. In fact, there are compelling reasons you should not spray your plants with Dawn or other dish washing liquid, and why insecticidal soaps are more effective and safer for your plants and the environment.
Let’s start with a chart that succinctly sums up the differences between two popular products — Safer Insecticidal Soap and Dawn Platinum Dish Detergent. Then you can read on to learn about the details and significance of the differences.
Insecticidal Soap vs Dish Detergent:
Summary Chart
| Safer Insecticidal Soap | Dawn Platinum Dish Detergent | |
| Soap/Detergent | soap | detergent |
| # ingredients | 1 ingredient | 28 ingredients |
| Source | derived from plant oils | synthetic |
| Organic materials seal | yes | no |
| Biodegradable | yes | partially |
| How it works | removes insect coating, does not damage plants | removes insect coating & protective coating on plants |
| Testing | tested to be safe & effective on plants | not tested on plants |
| Insects controlled | known | unknown |
| Proper dilution ratio | known | unknown |
| How & when to apply | known | unknown |
| Contraindications | known | unknown |
Dish Washing Liquid is a Detergent, Not a Soap (and why that matters)
Humans have been making and using soap for thousands of years. Soap, by definition, is made by combining fat with an alkaline substance. Originally, soap was made from animal fat mixed with ash. Later, vegetable oils (such as coconut or olive oil) replaced animal fat and potassium hydroxide replaced lard or tallow.
SOAP = animal or plant fat + alkaline substance
While Dawn and other dishwashing liquids are often referred to as soap, they are not soap! They are detergents, which are always made of synthetic chemicals.
DETERGENT = mixture of synthetic chemicals
It has become common to call household and personal cleaning products “soap”, but in fact, most are actually detergents. And there is an important difference between the way soap and detergents affect plants.
Detergents Kill Bugs But Harm Your Plants
Both insecticidal soaps and dish detergents work by stripping insects’ outermost protective coating so they dry out and die.
But detergents are harsh strippers which contain surfactants, molecules that decrease surface tension to remove wax and oil. This works great when cleaning greasy dishes, but causes problems when used on plants.
Detergents Destroy Plants’ Protective Layer
Plants have many ways to protect themselves and one of them is having an outer waxy coating called the cuticle.
The cuticle in plants has 3 main functions.
- It creates a barrier to prevent water loss by transpiration.
- It forms the first line of defense against pests and pathogens.
- It screens out excessive UV light.
As you can imagine, these are extremely critical functions — especially for plants in the desert!
Detergents not only remove the waxy coating on insects, they also strip the protective coating off your plants.
Compromising a plant’s cuticle layer leaves it more vulnerable to disease, water stress, and ironically, further insect damage.
Safer Soap vs Dawn: Ingredients Compared
Many gardeners reach for home remedies expecting they are more natural, but in this is definitely not the case when it comes to dish liquid versus insecticidal soap.
According to Iowa State University, most dish washing liquids contain “power scrubbers,” antibacterial agents, fragrances, lotions, and surfactants to reduce the surface tension of water and make it “wetter.” These additives may be phytotoxic (i.e., kill plants).
I’m going to compare two popular products — Safer Insecticidal Soap and Dawn Platinum Dish Soap. (Proctor & Gamble currently has more than 30 versions of Dawn, so I picked one that seemed representative.)
Safer Insecticidal Soap contains one ingredient — potassium salts of fatty acids. It’s produced by adding potassium hydroxide to fatty acids found in coconut, olive, and other plant oils. (This is a modern version of combining fat and ash to create soap.)
Dawn Platinum Dish Soap contains the following ingredients, according to this product’s “SmartLabel.”
- Sodium Lauryl sulphate
- C10-16 Alkyldimethylmine oxide
- C9-11 Pareth-8
- Deceth-8
- Alcohol Denat.
- Sodium Chloride
- Tetrasodium Glutamate Diacetate
- PEI-14 PEG-24/PPG-16 copolymer
- Sodium Citrate
- Fragrance*
- PPG-26
- Phenoxyethanol
- Methylisothiazolinone
- Acid Blue 9
- Acid Red 33
*The number of ingredients is larger than this, since their fragrance alone contains 14 ingredients.
You don’t have to be a chemist to see that there’s nothing “natural” about this product. Even the “everyday” ingredients listed here such as fragrance, colorings, and sodium chloride (i.e., salt, a known plant-killer) are not things I want in my garden or on my plants.
Procter & Gamble is vague as to whether Dawn is biodegradable. On their FAQ page they state, “Our dish soaps contain biodegradable surfactants” and cagily avoid discussing the many other ingredients.
If you’re interested in learning more about the safety of specific ingredients, you’ll find a discussion of their environmental and health effects at the Environmental Working Group. (They give Dawn Platinum Dish Soap an overall score of “D”.)
Insecticidal Soaps: Proven Safe & Effective
Insecticidal soaps are tested to be safe and effective on plants. When you buy a product like Safer, you’ll find instructions on proper dilution, what insects it’s designed to control, and how and when to apply. You’ll also find their OMRI Listed® seal (Organic Materials Review Institute).
Properly registered and EPA-approved insecticidal soaps are usually 1 to 2% soap by volume. This dilution ratio is the sweet spot that minimizes damage to plants while still effectively controlling pests.
But when you’re using Dawn or any other dish detergent, you’re either on your own to figure it all out or you can follow dubious online advice and hope for the best.
If you have your heart set on using a DIY formula, a Castille soap like Dr. Bonner’s should be safer for your plants than Dawn since it’s made with vegetable oils and potassium hydroxide. It’s a true soap, not a detergent. But determining a safe and effective dilution will still be hit or miss.
Before using any bug spray, ID your bug to
make sure it’s not a beneficial insect.
Then start with a jet spray of water.
Insect sprays including soaps are not selective —
they kill both good and bad insects.
Insecticidal Soap Exceptions
There are several common plants that are known to be sensitive to sprays that affect insects’ waxy coatings. So you should not spray these with either insecticidal soap or dish detergent. Those that are sometimes grown in the desert include:
- conifers
- crown of thorns (Euphorbia milii)
- gardenias (Gardenia spp.)
- geranium (Geranium spp.)
- jade plant (Crassula argentea)
- lantana (Lantana camara, L. montevidensis)
- moss rose (Portulaca grandiflora)
- nasturtium (Nasturium spp.)
- palm trees (Arecaceae family)
- poinsettia (Euphorbia pulcherrima)
- redbuds (Cercus spp.)
- “some” succulents**
- sweet peas (Lathyrus odoratus)
Cautions!
But before spraying any plant with any product,
test it on one leaf and wait 24 hours.
If you see any signs of stress, do not use.
**Use with particular caution on succulents
which depend on their waxy coating for survival.
Never spray plants with anything other than water
when the temperature is over 90℉.
Why All the Hype About Dawn?
Before we go, let’s revisit why Dawn is so often included in DIY solutions of all kinds, and is often promoted as being natural and safe for the environment and wildlife.
There is nothing special about Dawn that makes is superior in the garden. (It might excel at washing dishes, but that’s outside my purview.)
Proctor & Gamble, the maker of Dawn, has done an outstanding job of greenwashing, a marketing technique that makes products and companies seem more environmentally friendly than they are. They’ve done such a great job, that they now have an entire fleet of social media influencers promoting their products.
Many purport that Dawn products are natural, which is clearly not true. (Just the color should be a give-away. Nothing in nature is that color blue!)
CBC, Canada’s national public news service, did an investigation of false environmental claims in their article 10 Worst Household Products for Greenwashing and at the top of the list was one of the Dawn dishwashing products. Here’s what the article has to say.
“The labels on Dawn’s antibacterial dish soap feature baby seals and ducklings with the promise that Dawn helps save wildlife. Dawn donates soap to clean up animals after oil spills and gives money to rescue groups, but the product itself contains an ingredient harmful to animals.“
Proctor & Gamble refused their interview request.
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Author Bio
Deane Alban is the creator of Southwest Gardener. She is a science writer with a bachelor’s degree in botany from the University of South Florida. Gardening is her lifelong passion. She’s been gardening in Tucson for 15 years.
