You’ve probably come across more than a few homemade recipes for gardening. One of the more popular types of recipes for getting rid of pests is easily made with regular dishwashing liquid and water! Keep in mind:
Insecticidal soap is a fairly harmless solution to pests but dish soap can kill the plant’s leaves and contaminate the soil. Dish soap should be used as a last resort if you have no insecticidal soap. If you use dish soap, spray it directly on the pests and spray the plant off with water afterward.
How often should you be spraying soap on your plants?
As a whole, the biweekly application of soapy water to plants is enough to get rid of pests. It’s crucial to spray directly on the insects, coating them entirely. However, this homemade dish soap mixture may kill beneficial bugs and damage plants due to its additives and varying concentrations.
If you want to know about alternatives for dealing with pests that don’t contaminate your soil and possibly cause your plants to lose a bunch of leaves like dish soap… check out this article: How to Rescue Plants from Common Houseplant Pests & Diseases
Petunias and dish soap treatments seem to be all the rage, if that’s you, take a look at our article on treating petunias with dish soap and other alternatives.
Below, I elaborate on how homemade insecticidal soap affects plants, along with instructions and tips for using them:
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Table of contents
What Happens When You Apply Soapy Water to Plants?
Plants have a waxy cuticle covering their leaves to protect them from invading pathogens and loss of water and nutrients. This protective layer can be stripped entirely or weakened when soap is introduced, causing dehydration and increased susceptibility to diseases. Common damaging marks you’ll find on soap-treated plants are dried & scorched leaves, yellowing, and dead brown spots on the foliage.
This is more prominent when using homemade soapy mixtures. But that doesn’t mean insecticidal soaps won’t do such damage. Applying either will always include the risk of phytotoxicity, i.e., plant damage. However, the risk is significantly higher with DIY insecticidal soap solutions.
Standard insecticidal soaps have active ingredients that are regulated and, most importantly, consistent. These are specifically made to target soft-bodied pests such as aphids and are meant to be of less risk to beneficial bugs. However, it can still potentially cause plant damage but only if the mix has too high a concentration of soap. Remember, high soap concentration = damage. It’s also worth noting that hard-skinned insects such as beetles can be dealt with using these soaps, but not homemade ones.
On the other hand, dishwashing soaps and detergents are ever-changing with varying additives such as degreasers and fragrances. Your plant is already stressed from pest problems, so dealing with additional damages from harsh chemicals may lessen its chances of recovery. A better option if you’re really in a pinch is to choose a dishwashing liquid with little to no additives.
If your plants aren’t being bothered by insect pests, are outside, and you are seeing signs of pathogens eating your plant’s leaves, take a look at your watering habits. You may need to change the time of day you are watering in order to avoid fostering more pathogens in the future. Check out our article: When Is the Worst Time to Water Your Plants? if you want to know when you should be watering.
Is it alright to spray plants with soapy water?
As a whole, be careful when spraying plants with soapy water. There is a risk of causing foliage damage due to the harsh chemicals in soap. Where possible, follow the soapy application with bursts of water to remove any residue after use.
How Do I Make a Soapy Solution To Get Rid of Pests on My Plants?
- Prepare a gallon of water. It’s safer to use filtered water or distilled water, as it has a tiny amount or no chemicals. Tap water is fine, but only if you don’t have hard water in your area. The high mineral content of calcium and/or magnesium in the water will cause the soap to be less effective against pests. You can quickly check if this is the case by mixing some soap in the water and leaving it to stand for an hour.
- If scum appears at the top of the water, then you have hard water.
- If the mixture remains cloudy or chalky, your water can be used for your homemade insecticidal solution.
- Choose a liquid dishwashing soap with little to no additives. As mentioned, the fewer chemicals in its ingredients, the less chemical stress you’ll place on your plants during application. But always remember that this doesn’t mean your plant will be off scot-free of phytotoxicity risks.
- Pour 1-2 tablespoons of soap into the gallon of water and mix well. This measurement will vary depending on the type of soap you choose. The more concentrated it is, the less dose you’ll likely use. It’s best to start with the smallest measurement first and test things out with that first. Only increase the liquid soap dosage one increment at a time if it’s ineffective in killing off the pests.
Tips & Precautions on Spraying Soapy Water on Plants
You can’t prevent phytotoxicity risks, but you can minimize them to give your plant a fighting chance. Here are a few ways to do just that:
- Look up your specific plant to see if it is sensitive to insecticidal sprays. Some plants are naturally more delicate than others and will likely start to die immediately if you spray them all over at once.
- Always test-spray your soapy solution on a leaf to gauge the plant’s sensitivity. This is a vital precaution you need to take with any solution you’re spraying onto your plants. After spot-spraying on a leaf, leave for 2 days before checking on that spot again.
- If there are no visible damages, feel free to spray the rest of the plant.
- If there is some damage, readjust your solution and dilute it further.
- Do not spray the soapy solution on your plant when it is too hot and humid. During this time, your plant is stressed and wilting from the intense heat. You risk them getting damaged easily. Not only that, the solution will evaporate almost instantly once applied due to the heat and not stick to the pests as it should.
- Only spray the soapy solution during the early morning or late evening. This allows the mixture to stay wet longer to work its magic on the pests and kill them off. It also helps you avoid accidentally killing off any beneficial insects because they are rarely around during this time, especially in the morning.
- Give your plants a burst of water to spray off the soapy solution the next day. This eliminates any dead pests, but it also washes off any leftover soap residue on the plant.
- Where possible, use alcohol swabs and bursts of water to get rid of the pests first before looking into using insecticidal soaps, homemade or commercial. Unless your plant is heavily infested, try not to grab the soap immediately to get rid of them. You want to minimize any further stress to the plant, so it’s advisable to first use all the other methods. If you really have no other choice and the pests are uncontrollable, by all means, go for the killing spray. You can read more about handling pests in your plants in this article.
Final Words
As with any homemade gardening solution, it is also always better to take unwarranted social media advice with a grain of salt until you do enough research to see if evidence exists to back the advice up. There is almost always some level of truth to grand claims but, most times, like this time, they omit the potential risks.
Keep in mind that pretty much any insecticidal solutions sold in stores or made at home can be over-applied or could cause adverse reactions for some plants. For instance, a mixture of 5% peppermint oil and 95% water is a decent mealybug control spray, but, over-applying it (or not spraying the plant off with water quickly enough after treating it) will cause more leaf damage as a result. I also wouldn’t use over 5% peppermint oil on plants or neglect to spray off the plant. I found out the hard way, with a 10% solution you can easily make a jade plant lose all its leaves. And just to prove the point (although I don’t advocate a 10% solution) a passionfruit vine will put up with 10% and only lose some leaves but its leaves will get many brown spots. Every plant reacts to things differently. Always apply lightly then wait for adverse reactions. Don’t go overboard to purge your plant of pests all at once, you might end up heartbroken after realizing what you’ve done.
So be careful when trying those handy tips fellow plant owners! Happy planting!
References:
https://hgic.clemson.edu/factsheet/insecticidal-soaps-for-garden-pest-control/
http://www.ladybug.uconn.edu/factsheets/insecticidal-soaps.php
https://ento.psu.edu/files/insecticidal-soap
https://ipm.missouri.edu/MEG/2016/7/Insecticidal_Soaps_An_Eco-friendly_Method_of_Pest_Control/
https://blogs.k-state.edu/kansasbugs/2020/06/12/fundamentals-of-using-soaps-as-insecticides/
https://edis.ifas.ufl.edu/publication/IN1248
https://aggie-horticulture.tamu.edu/plantanswers/misc/insectsoap.html
https://extension.umd.edu/resource/insecticides-fruit-pests
https://www.extension.iastate.edu/news/2007/nov/071601.htm
https://extension.umn.edu/yard-and-garden-news/coming-clean-soap-garden
https://extension.colostate.edu/topic-areas/insects/insect-control-soaps-and-detergents-5-547/
https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=18009
