By Erin Huffstetler | 06/05/2020 | 5 Comments
This post may contain affiliate links. View our disclosure.
Battling aphids, thrips or another garden pest? This homemade insecticidal soap will help you get the problem under control cheaply, and without the use of harmful chemicals.
I used this recipe to eliminate a massive thrip infestation in my garden last month.
I’d been so wrapped up in the busy-ness of life that I hadn’t even realized I had an issue, until one of my kids mentioned that there were little black bugs all over the chives. Uh oh!
I went out to investigate, and this is what I found ….
I didn’t want to lose our chives, or have the infestation spread to another part of our garden, so I went back in the house, mixed up a batch of my homemade insecticidal soap, and doused those suckers down.
Then, I repeated the process a few days later to kill any thrips I’d missed the first time.
And it took care of the problem. Now the thrips are gone, and my chives are starting to grow back.
I try to keep thrips and other garden pests in check by planting flowers to attract beneficial insects that prey upon the bad bugs, rotating crops, practicing companion planting and following other organic gardening methods.
But I hadn’t ever had an issue with onion thrips before, so I didn’t have any of these measures in place. Looking back, I probably could have avoided the whole problem, if I’d simply planted some marigolds near my chives.
(Marigolds attract pirate bugs, which are a natural thrip predator).
You can bet I’ll be sprinkling some marigold seeds over there now.
I’m just mentioning this because treating plants with insecticidal soap is my solution of last resort. While my recipe is non-toxic to animals and birds, I still prefer to let nature take care of things, and I only intervene when things get seriously out of balance.
And when it does become necessary for me to address a garden pest – be it insect or animal – I try to figure out how the problem could be avoided in the future. Relying on insecticides – even non-toxic ones – is never my goal.
How Insecticidal Soap Works
So, I told you the insecticidal soap that I mixed up eliminated my thrip problem, but how did it do that? It’s simple really. Insecticidal soap – whether store-bought or homemade – is just a mixture of liquid soap and water. Sometimes it contains other things, like vegetable oil, cayenne pepper or garlic, but you really only need soap (the active ingredient) and water (to dilute it).
The fatty acids in the soap suffocates some pests, and dehydrates others (by removing their waxy protective coating).
The water is just as important. It dilutes the soap to a level that won’t harm most plants.
It’s a ridiculously simple formula, but highly effective.
My recipe for insecticidal soap also contains vegetable oil. It’s optional, but it keeps the insecticidal soap wet longer. And that’s important because as soon as the soap dries it stops working.
Insecticidal soap works best on soft-bodied insects, like aphids, thrips, white flies, spider mites, mealybugs, earwigs and caterpillars (including those annoying tent caterpillars). And it’s effective against adults, larvae and nymphs.
It also helps with powdery mildew. Just spray it on the affected areas.
Earlier I mentioned that I use insecticidal soap to eliminate pests that have gotten out of hand, but I should mention that I also use it to treat any plant that I bring indoors for the winter. I don’t want to inadvertently spread pests to my other houseplants, so I always give plants a good dousing before bringing them back inside.
My insecticidal soap can be used on vegetables, fruits, flowers, trees and houseplants.
Plants You Shouldn’t Use Insecticidal Soap On
According to Clemson University, you shouldn’t use insecticidal soap on bleeding heart, cherries, crown of thorns, Easter lilies, gardenias, hawthorn, horse chestnut, Japanese maple, lantana, maidenhair fern, mountain ash, nasturtiums, portulaca, plum or sweet pea.
They further warn against using insecticidal soap on conifers during a drought, but really it’s best not to treat any plant during a drought.
Azaleas, begonias, fuchsias, geraniums and impatiens are also listed as being somewhat sensitive to insecticidal soaps. Inspect treated plants a few hours after application, and if you see signs of wilting, or browning, rinse the plants thoroughly, to remove any remaining soap.
Some plants have a waxy leaf coating that gives them a bluish color. If you have any plants like this in your collection, think twice about treating them with insecticidal soap. The soap could dissolve the wax coating, and take away the blue tint that makes the plant special.
If you’re worried about how a plant will react to insecticidal soap, do a spot test. Then, wait 24 to 48 hours, before proceeding with a broad application.
Homemade Insecticidal Soap
Now that you know a little about how insecticidal soap works, and when you should use it, let’s get on to my super-simple recipe.
To make it easy for you to make as much or as little as you need, I have both a one-gallon and a one-quart version of the recipe. I mix the one-gallon version up in a one-gallon sprayer, for quick and easy application. I have a dedicated sprayer that I only use for this purpose. This avoids any chance of accidental contamination.
An empty spray bottle works great for the one-quart recipe.
Tip: Write the recipe on the side of your sprayer or spray bottle, so you won’t have to look it up the next time you need it.
To avoid damaging plants, it’s important to use liquid soap – not detergent – in your insecticidal soap. Detergents (including dish soap) contain additives that could harm your plants. For the best results, stick to a mild soap, like liquid castile soap.
This recipe makes a 1% insecticidal soap solution. Most commercial insecticidal soaps contain 1-2%.
1-Gallon Insecticidal Soap Recipe
- 1 gallon water
- 2 1/2 Tablespoons liquid soap
- 1 Tablespoon vegetable oil (optional)
1-Quart Insecticidal Soap Recipe
- 1 quart water
- 2 tsp liquid soap
- 3/4 tsp vegetable oil (optional)
If you have hard water, use distilled water (or bottled water) in this recipe. Hard water will make the soap less effective.
How to Treat Plants With Insecticidal Soap
Spray on the front and backside of leaves, and in the soil around the plant. Insecticidal soap is a contact killer, so you’ll only kill the insects that you spray.
Don’t apply insecticidal soap during the heat of the day. This could burn the plants. Instead, apply it early in the morning, or in the evening. This will cause less stress for the plants, and the soap won’t evaporate as quickly. Bees and beneficial insects are also less likely to be active during these times, so there’s less chance of harming them.
Repeat the treatment three days later, to kill any pests that you missed the first time.
This insecticidal soap won’t leave harmful chemicals on the plants or in the soil, and it won’t harm birds, animals or most beneficial insects. It’s food-safe, too. You can spray it on edible plants, and eat them the same day.