Dish Soap like Sunlight or Dawn is a regular addition to home pest control remedies for the garden. You use dish soap every day and eat from the dishes you clean with it – how can it be harmful to plants? It’s time to look through the bubbles and see the truth.
Dish Soap – What is It?
Dish soap is a generic term, but it usually refers to the liquid soap products used for washing dishes. Dawn, Joy, Palmolive and Sunlight are very common brand names. It also goes by the names Dish washing liquid, washing-up liquid, dish washing soap, and dishwasher detergent.
Dish washing soap is a detergent that can include phosphate, bleach, enzymes, dyes, fragrances and rinsing aids.
Scientists distinguish between soap and detergents which, chemically, are quite different. Soaps are cleaning agents made from natural oils and fats. Detergents are cleaning agents made from synthetic chemicals called surfactants. Soap and detergents both clean, but the chemicals in the products are different.
Dish Soap is actually misnamed. It should be called Dish Detergent. You will see why this is important in a few minutes.
Dish soap works by dissolving greasy chemicals like oils, fats and waxes and it is excellent at this job. It is also a powerful degreaser.
Insecticidal Soaps – What Are They?
Insecticidal soaps are pesticides that are used in the garden. I’ll talk more about how and why to use them below.
Insecticidal soap is a true soap, not a detergent.
A soap is made by mixing together sodium hydroxide, or potassium hydroxide with fats. The final product is something called either sodium salt of fatty acid, or potassium salt of fatty acid. This is the same ingredient found in most bars of soap, and in liquid hand soap. Chemically these are very different from detergents, although both clean things.
Insecticidal soap is a special kind of soap. It is made using only potassium which produces a milder, softer soap than sodium. It also uses long chain fatty acids – a special type of fat. This soap is specially made to be mild on plants.
Soaps will also dissolve greasy chemicals like oil, fat and wax, but they are not as good at this job as detergents. From a cleaning perspective insecticidal soap is a great soap.
Dish Soap On Plants
What happens when you spray diluted dish soap on plants? Remember dish soap is a detergent that is excellent at removing oil, grease, and wax. When you spray it on your plants, it removes the natural oils and waxes that all plants have on their leaves. These oils and waxes serve to protect the leaves.
When the protective coating is removed from the leaves, it makes it easier for pathogens to get a foothold and infect the plants.
Spraying your plants with dish soap removes their natural defenses against pests and diseases. You are setting the stage for your plants to get sick, and maybe die.
DIY Insecticidal Soap
There are many DIY home recipes for making insecticidal soap. The problem is that NONE of them are insecticidal soap. If they use dish soap – they are detergents, not soaps. If they use liquid hand soap, the fatty acid salts are made from short chain fatty acids which are phytotoxic to plants – they damage plants. You can’t make insecticidal soap using things you find around the house.
One recipe on the internet says “Use a pure liquid soap… Don’t use detergents, dish soaps, or any products with degreasers, skin moisturizers, or synthetic chemicals. ” Soap is a synthetic chemical!
Will the homemade insecticidal soaps get rid of insects? Maybe, but they will also damage and weaken plants.
Is Dr. Bronner’s Castile Soaps Safe?
Castile soaps, of which Dr. Bronner’s is a popular brand, are made from vegetable oils (particularly olive, palm, and coconut) using potassium hydroxide. So they are potassium based soaps and therefore many people claim that they are the same as insecticidal soap. Most castile soaps are mixed with fragrances and essential oils for a wide range of uses but not as insecticides. This soap maybe safer than other sodium-based soap, but nobody really knows what the additives will do to plants. Since it is not labeled as a pesticide it should not be used.
Use Insecticidal Soaps Correctly
My post, Insecticidal Soap – Use it Correctly, provides more detailed information on how to use these products. In summary, they are only effective if you spray the insects – not the plants. Insecticidal soaps are much less harmful to plants, but even they should not be used to cover the whole plant. Although, fairly safe for plants, they will harm certain plants – look at the instructions an keep away from sensitive plants.
Wish I would have seen this earlier. Thank you! You think a jalapeno pepper spray would work? Like using a plant to help a plant.
I love that I found this! I am one of the people that thought Dawn was fine for the environment since they use it to clean animals that have been caught in oil spills. I do have a question though, are natural soaps safe for the soil? I am doing a final project in my Natural Resources class on switching cleaning products to all eco-friendly (I still have a few I haven’t switched over yet) and also moving my grey water drain to feed into my vegetable garden to help save on water. I am trying to change all cleaning products that go down the kitchen sink to be safe enough that I won’t need to get an expensive filter for this.
Natural does not mean safe. To understand how safe any product is you have to look at each chemical component in it.
So yesterday I did this spray on my cherry tree tomatoes plant … noticed the “curling, paper-lined, bronzed-spotted” leaves today. Is it too late to wash off?? Is the damage done? Is there a chance my tomatoes will still continue to grow? I currently have green tomatoes on them now
Depends on many variables.
I would just use regular dawn diluted, wait an hour or two, rinse off the plant thoroughly (which also rinses a bunch of aphids/ caterpillars/ beetles) then treat again while wet. At night or during overcast/ rain, you can kill all the bugs, very minor injury to the plants, and saponify the soil underneath (make more viscous/ hold water) but you gotta keep running that water for a while, rinse it super good (no answer for soil fungi and microbes, my plants usually like it better without things eating them, than not enough things helping them.) that is all.
Why use a product that you know is harmful to plants?
He or she is right. I used dawn dishsoap and water on the leaves of my plants like many people and websites suggested and the next day I went to look at my plants and all of my leaves are dead and crunchy. My heart dropped when I saw it.. 🥺
Is there an essential oil or something I can use to get rid of the soap? I wish I saw your article before I sprayed my plants! My bell pepper plants are dying 🙁
It will wash off with water.
Dealing with an aphid problem. Almost every site I go to suggests using dish soap, like Dawn to make some DIY pesticide.
After reading your guide, I’m afraid it’ll damage my tomatoes, but I don’t want to use anything too harmful to get rid of the aphids. Soap seems to be the best choice but the tomatoes are still new to the yard as I just transplanted them and don’t want to harm them with soap.
For reference to what I’m reading:
https://www.bugwiz.com/get-rid-of-aphids/
You can see that using dish soap seems to be safe and they say that as long as you use the soap carefully you should be OK, but your guide contradicts that. Now I’m unsure. Any thoughts?
Depends on the contents in the soap, and the concentration used. Damage to plants may not be easily seen by the eye. If you remove some protective coating on the leaf, the plant may replace it before insects attack.
For aphids – just spray with water.
It is against the law to call anything “SOAP” that isn’t made by saponification of fatty acids and Potassium hydroxide or Sodium hydroxide. If it says “Soap” it’s soap. While it may or may not have other ingredients that may or may not be harmful to you and/or your plants; soap is soap.
Things like “Body Wash”, “Dishwashing Liquid” and “Shampoo” are detergents.
You can make pure castille soap by soaking burnt wood / ash until an egg will float in the water and adding olive oil and mixing to saponify… this will make pure liquid castille soap. Is that a synthetic chemical?
Commercial Insecticidal soaps instruct you to wash it off with plain water after an hour or so to avoid damaging leaves. If you do this you can avoid killing your precious plants. You can kill your plants with commercial or homemade insecticidal soap, your choice but to avoid it, wash it off.
Re:”law to call anything “SOAP””. There is always a big problem with such a statement. Every country has their own laws, and even in the US different states and different organizations might have their own regulations. The FDA does not say how soap is made in order to be called soap. https://www.fda.gov/Cosmetics/ProductsIngredients/Products/ucm115449.htm
What is a synthetic chemical? There is no clear definition of this. Many processed chemicals are quite acceptable to organic certified farmers but they would never use so-called synthetic chemicals.
I was surprised by your comment “Commercial Insecticidal soaps instruct you to wash it off with plain water after an hour”. I have never heard this before. A quick Google for a manual and this is what I found. Clearly this is not part of the instructions for all products. http://florawww.eeb.uconn.edu/msds/insecticidal_soap_label.pdf
Nor does the Safer product recommend washing with water: http://woodstream.scene7.com/is/content/woodstream/safer/us/Resources/Instructions/sb%5Fus%5Finstructions%5F5118.pdf
Mild dish soap solution Killed my beautiful plant!!!!! I had bought this plant and it was already dying and after 5 years (a labor of love) it grew from a 3 inch twig to a 19 inch beauty and now all the leaves are falling off. It has been 4days from treatment for mites and death to my plant. When I asked for help no one answered. Thanks for the mite solution but you should tell people it might be at the expense of their Plants!!!
Hello, Sir
I did add some fairy liquid dish soap to water and then sprayed it on my lawn, but unfortunately my lawn suffered a bleaching , 3-4 days following spraying the solution. The bleaching was not serious, but obvious.
It was a light frost 3 days after the application, the bleaching was patchy across my lawn. fortunately the new grass is coming through on my lawn. Could you please, tell me what was the reason? Thanks for your time and I look forward to your reply?
Regards
Kima
As I said in the post, dish soap is toxic to plants.