3 Organic Aphid Control Methods — Tested

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When you discover aphids in your garden, you naturally want to get rid of them — fast! With a host of organic aphid control solutions available online, how do you know which one to choose?

If you’re like me, you want something easy. And more important, you don’t want your actions to harm your garden or your plants.

In this episode of the Beginner’s Garden Podcast and in the blog post below, I share with you how I tested 3 organic aphid control methods — homemade insecticidal soap, Neem oil, and worm castings — side by side.

I also share a fourth organic aphid control method that is always my go-to way to keep aphids from harming my vegetable garden.

Click below to listen to the podcast episode or continue reading.

My Aphid Control Experiment: Method

aphids on pepper plants

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In the early spring I discovered aphids on my pepper plants that I had started indoors. Because I had always heard about organic aphid controls but had never tried them in the garden, I decided I would test them for fun in my indoor planting.

I put to the test 3 common organic methods for aphid control: homemade insecticidal soap spray, Neem oil, and worm castings. During the experiment, I kept these plants indoors (including a control group) during the testing period. I wanted to ensure no natural aphid predators would skew the results (or suffer harm in the process).

Homemade Insecticidal Soap for Organic Aphid Control

Insecticidal soaps — both homemade soap spray and commercial blends — is a broad category and there are many options for the home gardener. I didn’t have any handy, so I found a recipe to make my own. I mixed 1 tablespoon of Dr. Bronner’s Peppermint Castile Soap in a quart of water, and I sprayed one section of pepper plants with this mixture.

Insecticidal soap works by landing on a soft bodied insect and dissolving the outer coating so that the insect dehydrates. If you make your own homemade soap spray, be careful to use a pure soap without other additives like anti-bacterial ingredients that could burn the plant. Always test a small section before dousing your entire plant, especially when using a homemade spray.

Neem Oil for Organic Aphid Control

The second organic aphid control test I performed was using Neem oil. Neem oil is a highly touted organic pest control remedy, but when you go to purchase it, you’ll find several options.

You can buy either 100% cold pressed Neem Oil, or clarified hydrophobic Neem Oil. What’s the difference?

Neem oil comes from the seeds of a neem tree. When it is cold pressed, the main ingredient is azadirachtin which works by disrupting the insect’s feeding, molting, and egg laying. The insect is poisoned by eating the azadirachtin on the plant.

Neem Oil blends containing clarified hydrophobic extract work in a different way. This extract is the solution remaining after the azadiractin is removed from the neem oil. Also effective for aphids, more like the insecticidal soap it works as it makes contact with the insect instead of by ingestion.

I used 100% cold pressed Neem Oil for my experiment. (Here is a similar brand to what I used.) I mixed 1/4 ounce of 100% cold pressed Neem Oil per quart of water. I also added a few drops of unscented castile soap to help the oil emulsify in the water. A pure dish soap would work just as well.

organic aphid control methods

Worm Castings for Organic Aphid Control

Worm castings for aphid control? I had never heard of this either until Joey and Holly Baird of the Wisconsin Vegetable Gardener Radio Show gave me this recommendation.

I applied 1 Tbsp of organic Earthworm Castings (similar to this brand) to each pot of peppers and I watered them into the soil.

It seems to be a little bit of a mystery, but one theory is that worm castings contain chitinase and as the chitinase is taken up by the plant, aphids eat it and it breaks down their exterior.

Aphid Control Experiment Results

(In the video above, you can see the results of each test, or keep reading.)

Day 1– The insecticidal soap removed all aphids in just one day. By comparison, approximately 80% of the aphids had been killed on the plants with Neem oil, and the plants with the worm castings had significantly reduced aphid population but not as much as the other methods.

Day 2– The plants with the insecticidal soap started to show minor leaf curling. With the Neem oil, there was a slight amount of leaf curl but not as much. This could be because I added some Castile soap to my mixture or because I didn’t realize I shouldn’t have applied it and immediately placed the peppers under my grow lights. By comparison, the plants with worm castings did not show any signs of damage and all of the aphids had died.

Day 3 – All detectable aphids on all plants in each of the three groups had died.

If all three organic aphid control methods killed the aphids on my peppers, how did the control group — with no intervention — compare?

The control group started with the fewest number of aphids. However, a week later the aphids had taken over those plants. After the conclusion of the experiment, I used worm castings on these plants so I wouldn’t lose my them. Within a few days, those plants with the worm casting application showed no signs of aphids either.

Another interesting fact: about a week after the conclusion of the experiment, I planted my peppers in the garden. Even though I have seen aphids on other plants, I have not noticed them on the peppers.

Best Method for Organic Aphid Control and Prevention in the Garden

Even though all three of my tests proved effective against aphids, my first recommendation to any gardener battling aphids is to let nature do its work. In other words, don’t step in unless you absolutely have to.

But why?

Aphids, also known as the “salad bar of the insect world,” will draw beneficial insects to your garden. These insects will help to control both aphids and other pests.

What’s wrong with using organic aphid controls in the garden? Many people don’t realize even organic pest control sprays, such as insecticidal soap and Neem oil, can kill the very insects that you want in your garden. That’s why I recommend saving those controls for the most desperate of circumstances.

Beneficial Insects for Aphids

What eats aphids? If you want to let nature do her work and take care of the aphids in your garden, you need to be able to identify some of the major players in the aphid hunting game.

Ladybugs Eat Aphids

ladybug adult and ladybug larva

First up, we have ladybugs, the princesses of the organic garden. While most people understand adult ladybugs are good, they may not be able to properly identify the ladybug larvae — the primary aphid hunters.

It is said that ladybugs can eat up to 5,000 aphids in their lifetime. It starts, though, with the adult ladybug finding food for her future progeny. She will scout out plants with high populations of aphids and choose to lay her eggs there.

When I look at my garden and take note of the tomato plants with the highest population of aphids, I usually find a few adult ladybugs on the plant within a few days. In one observation, I noticed almost all of the aphid population on one tomato plant had been eliminated in just ten days.

Syrphid Fly Larvae Eat Aphids

Syrphid flies, also known as hoverflies, can go undetected to the untrained eye. Looking more like a bee, you’re probably likely to view it as more of a pest or a nuisance. But this two-winged fly seeks out aphids, like ladybugs, for her young. And like ladybugs, syrphid fly larvae look more like worms, and if you’re not careful, you could kill these larvae thinking they are the bad guys.

syrphid fly adult and syrphid fly larva

Lacewings for Aphids

Lacewings, also known as aphid lions, also hunt aphids in the garden. Like the ladybug, the lacewing adult seeks out plants with aphids present before she lays her eggs.

I’ve known lacewings to be hard to find in the garden because they flutter almost like a butterfly and rarely land on a leaf long enough to spot, but if you’re looking, you can identify the lacewing adult by her “lacy” green wings.

green lacewing

How to Attract Beneficial Insects to Your Garden

If ladybugs, syrphid flies, and lacewings are the special forces in your fight against aphids, how do you attract them to your garden? I’ve found that by using two simple methods, you’ll notice your beneficial insect population increasing year after year.

First, you can attract beneficial insects to your garden by not spraying your aphids. First, the spray can harm larvae of our beneficial insect friends. But second, the beneficial insects must have food — aphids!

I have watched my garden this year and as I saw more aphids on my tomato plants, I started to notice more lady bugs, syrphid flies, and lacewings showing up. Yes, you have to be willing to let your plants withstand some damage, but healthy plants can take more than you think.

Second, plant flowers that attract these beneficial insects. I find ladybugs just about everywhere, but syrphid flies tend to show up near calendula and blackberry flowers. Any flowers with small pollen centers are perfect for adult beneficial insects.

syrphid fly or hoverfly on calendula flower

Special Notes for the First-time Gardener

I have not always had these beneficial insects present in my garden in the numbers they are today. It has definitely been a process, seasons in the making.

I try to keep my organic insecticides to a minimum. I plant more flowers in my garden. And I’m always seeking to learn which insects are helpful and which ones will destroy my plants.

If you’re a first-time gardener and find aphids are damaging your plants without evidence of a beneficial insect to be seen, the three organic aphid controls I tested above would be a good place to start. I’d recommend worm castings, as it will not harm any potential beneficial insects. But if you must spray, use caution and make sure there aren’t any beneficial insects lurking around.

As you take steps to increase the beneficial insect presence in your garden, you’ll find yourself needing to rely on organic pest control methods and instead let nature do its work. It’s a beautiful process, but not always an immediate one. I hope that these strategies will help you in your quest for healthy plants and a healthy organic home garden.

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  1. Well, I certainly learned something today! Those pesky ‘sweat bees’ don’t look so pesky anymore! Now if I can just get them to pay more attention to my garden than me, LOL!

  2. Thank you very much for sharing your experiments with us, Jill!! I’m seeing a lot more aphids in my garden this year (probably due to the mild winter we had here = Brooklyn, NY), and I’ve been killing a lot of them by hand. But I will try the earthworm casting method now that I’ve read your article and watched your video! Thank you very much again, Jill!!

  3. Thanks – I might try the worm casting thing on my indoor plants. I seem to be allergic to just about everything you can spray about.

    Is it possible that it simply boosts the health and energy of the plant, giving it the resources for its natural defences to deal with the pests?

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