Insecticidal Soap for Garden Pest Control

Insecticidal soap spray can be a safe, effective weapon against certain garden pests.

| Aug. 11, 2009

Soap spray

Soap spray is safe to use in organic gardens because it has no residual effect and only kills insects that are sprayed directly.


So you’ve planted your garden, watered carefully and weeded diligently. Everything’s going well, until one day you notice clouds of tiny whiteflies swirling around when you brush your tomato plants. Don’t panic — natural enemies will usually move in against the little buggers, especially if you’re growing lots of flowers around the garden to provide nectar and pollen to support the beneficial bugs. But if you want to give Mother Nature a helping hand, you can use an insecticidal soap spray.

Soap spray has no residual effect and only kills insects that are sprayed directly. That’s what makes this mild insecticide OK in organic gardens. Insecticidal soap will kill many types of soft-bodied insects and mites, including aphids, young scales, whiteflies, psyllids, mealybugs, spider mites, boxelder bugs and Japanese beetles.

Soap sprays do have limitations, though. The soap may be mildly toxic to some plants. To minimize damage to plants, entomologist Whitney Cranshaw from the Colorado State University extension office recommends waiting four to seven days between applications, diluting the spray with water even more than the spray instructions recommend, and spraying the same plant as few times as possible.

Make sure to buy insecticidal soap in a concentrate rather than as a “ready-to-use” product, as this will save you a lot of money in the long run. For example, you can buy a 32-ounce bottle of spray for between $5 and $10. A concentrate will cost you about twice as much, but will ultimately yield about six times more spray. If your tap water is hard, use softer rainwater or distilled water to make your soap spray. “In hard water, minerals such as calcium, magnesium, and iron combine chemically with the fatty acids in insecticidal soap. Not only does this reduce the soap’s insecticidal activity, it can also cause increased leaf injury,” says Rodale’s Chemical-Free Yard and Garden.

Homemade soap sprays can be a low-cost alternative to store-bought sprays, but making your own spray can increase the risk of damage to plants. Commercial soap sprays are generally better because they are designed specifically to control insects and minimize plant damage.

If you decide to make your own soap spray, be careful which kind of product you use. While some soaps are effective insecticides, other soaps can act as herbicides, disrupting plant cells and damaging your garden. A good practice to ensure plant safety is to do a test spray on a small portion of the plant, and wait a few days to see if the spray does any damage before spraying the rest of the plant.

8/25/2009 6:33:39 AM

we have had great results using organic foaming soap in our spayer, we found it at a company called had it in foaming solution and we also tried hand bars of the unscented organic variety, we let it desolve in H2O and then sprayed. With the product being organic it worked well for us and we were less concerned on unhealthy side effects. S

connie kuramoto_1
8/15/2009 10:23:31 AM

Although I applaud the replacement of very poisonous pesticides with soap I am concerned that there is an aspect of plant biology that many scientists are neglecting. Leaves of healthy plants are covered with a protective layer of microbes whose function is to resist disease and aid in plant health. Spraying soap on leaves destroys these microbes. It is better to just wash the insects off with a spray of plain water. In the case of aphids the force of the water dislodges the aphids but because their sucking mouth-parts are so firmly set into the plant cells they are actually broken off. This prevents the insect from coming back to attack your plant. Remember that soap will kill both good and bad bacteria in the ecosystem, and the run off could also be killing good soil microbes. I have taught Horticulture for over 20 years now, and am constantly amazed at how we are still on a warfare rather then welfare strategy for our plant health management. Build up your soil, provide habitat for all creatures, encourage diversity, and you will have limited pest problems, no sprays needed at all!

8/14/2009 6:34:55 PM

I don't know if it would be considered insecticidal soap, but I have found something that really nails Squash Bugs. I use a 6 gallon sprayer attachment for my hose, with about a cup of dish soap, but I include a tea made from nestercians (sp) flowers and leaves. The bugs have only 30 seconds to a minute till they die. They must be hit with the juice but it is totally effective. We have tried a lot of things, but this stuff works wonders. I grab a couple of handfuls of the flowers and leaves and put them into an empty milk jug, and add boiling water. Next day I use it on the garden, doesn't seem to hurt the plants, I generally use it two days running to get all of the bugs and only in the evening, so I don't hurt the bees.

8/14/2009 5:04:16 PM

I've used baby soap when I make my insecticidal soap. I only put in one teaspoon to a 16 oz spray bottle and I also put in a tablespoon of canola or olive oil-- depending upon what I have on hand. This combination will only stun the insects and it won't work for fungus gnats. It will work for spider mites and aphids. I then, wipe the insects away with a paper towel. Once I finish, I spray with regular water to make sure there is no soap residue left. I have only used this on common houseplants with much success. I did use it on a tomato plant once, but the combination of the pests and the soap damaged some of the leaves. The tomatoes, however, are doing wonderfully and there is much new growth that promises a big harvest for the fall. Hope this helps others out there.

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