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.
Thank you, Robert. We try at GardenAtoZ.com to help gardeners understand the products, plants and processes they use and have no reason to write our own article about soap and detergent because you have covered it so well. We’ve referred our readers to your site. Especially glad to “meet you” because our daughter lives in Guelph, we are there often (but not this terrible year!) and did not know of your garden. Hope to meet you when the world returns to normal. – Janet Macunovich and Steven Nikkila —
Thank you very much. Hope to see you in my garden.
What can I do if I have wight powder fungus on my pot plants thatt I have on my balcony they have been doing great big all of a sudden I have this light gray or dust looking shit on the leafs they are just starting to bud and I’m not sure what to do there on my balcony I need some advice please
I sprayed my pepper with mixture of dawn soap and water. I washed it off after twenty minutes. Will my pepper plant survive?
Thank you for this article. It is a few days too late for my vegetables I’m afraid. I used a combination of 1c vegetable oil and 2Tblsp Dawn and 1c (hard) water. Now the leaves of my beans are browning and some of the blossoms are withering. Is it too late to try to wash it off? Will be all oil even wash off?
I’m sorry if this does not completely pertain to your article, but I cannot find the information anywhere online and I hope you might be able to help. I use Chlorogalum pomeridianum AKA wavy leaf soap plant to condition my soil. This year I have been adding mykos brand mycorrhizal inoculum and I’m not sure if the soapanins that naturally occur in this plant might hinder the beneficial fungi. Any insight you have would be greatly appreciated.
Please don’t follow any advise in internet .some didn’t wait to see the result so big hey can write for us, I have wash my beautiful plants with dawn detergent dish soap and majority of my leaves went dark ,dry and curled up. I felt so bad .this marijuana plant I am talking it’s been with me for 4 month(slow grown)and it’s hurting me that I hurt him.
I spry the leave all with fresh water for few time and as Robert said .time is healer :it didn’t dry right away and won’t heal right away.
Thank you me Pavlis for all.
Very helpful
my kids used our dish soap to make bubbles in our backyard. Little did i know that they spilled lots of soap on the pavement. When i went to wash all the soap it made never ending bubbles. this soapy water got into our garden area where i grow tomatoes and purselane. All the plants look gorgeous and very green, Will it be ok to eat our vegetables? The dish soap we use is from costco Ultra Shine biodegradable safer choice. I could not find any information in the web about this product.
yes.
Your website is phenomenal. I wish I had found your website before applying a mixture of water, vegetable oil and Dawn to spray my mint plant which had white spots all over it. When I woke up this morning, the leaves started to turn brown. I pruned the entire plant. Any chance I can revive my mint plant?
Hello Rob,
I have some experiment plants in our home for our children. We were growing some tomato seeds, bell pepper seeds, and a kidney bean, all in soil. Lately I’m starting to see more what I’m assuming are fungus gnats appearing near the plants.
I am glad that I researched a bit more and stumbled on your site before just going with the dish “soap” and water mixture to spray the soil. Is there a product that you recommend that will help these pesky gnats to stop multiplying and to just die off altogether, and that may help prevent a new infestation?
Thank you in advance!
Robert – Sorry if this is a repeated question, but what would you classify a bar of Irish Spring soap, used in the shower to be? Not dish or hand soap, but damaging to plants? I use a bar diluted in canister of water on my roses, phlox and butterfly bush after they’ve sustained deer damage. While they’ve bounced back, I’m not comfortable with the soapy streaks left on the plants leaves along with a couple dead bugs I’ve found likely subject to my spraying. Thanks for any insight!
You would have to look at the ingredients to see what kind of soap it is.