At some point, all gardeners have to deal with an insect invasion. Whether you garden indoors or out, whether you have a balcony garden or a back forty, bugs will sneak in and set up shop. Fortunately, there’s an easy trick for destroying destructive insects: homemade insecticidal soap!
It’s devastating to watch aphids chowing down on your prized fennel plants. Just as bad are squishy, white mealybugs that overrun your houseplants, leaving sticky residue behind.
For the eco- and health-conscious gardener, options for controlling these destructive pests often feel limited. We don’t want to poison the plant or our bodies, just the insects destroying our gardens. Fortunately, this soap is a fabulous way to get rid of them.
What is Insecticidal Soap?
An insecticidal soap spray is simply a mixture of fat-based soaps and water. That’s it! Then, you spray the mixture on the plants’ leaves, and on the tiny pests that devour them. The soap dissolves the membranes of the insect’s body, killing them through excessive water loss.
Sounds pretty gross, right? But it’s very effective.
There are dozens of commercial soaps on the market promising to safely and efficiently kill insect invaders. They’re a great option if you’re not interested in making your own spray.
Insecticidal soap is a 1-2% solution of soapy water. That said, most commercial blends err on the safe side with a 1% solution. This amount is safer for wilted, unhealthy plants, but less effective. In your homemade solution, try for a 2% solution.
The higher percentage of soap makes the spray impressively effective. Additionally, it won’t damage your healthy plants. If you have sick or damaged plants, however, give them time to recover before spraying.
So, What Kind of Soap do I Need?
Choosing the right soap is essential, since detergents like dish or laundry soap won’t work. Castile soap like Dr. Bronner’s or Fels Naptha are ideal. Shop around for the brand that works best for you.
Lard-based or goat’s milk soaps would works as well. The important thing is to make sure that the soap you use is fat-heavy. The fats in the soap are what kill your pests.
Make sure the soap you choose is pure soap. Don’t pick a product with added skin softeners, chemicals, or grease cutting power. These additions make the soap less effective as an insecticide. Furthermore, they may also poison your plants.
Stick to simple, pure products. Measuring and mixing up your spray will be easier with a liquid soap. You can grate a bar soap into easily dissolvable shavings, but liquid soaps will save you that extra step.
All the Ingredients
Putting together your insecticidal spray is easy. With only two ingredients, you’ll be all set to start spraying the invaders on your plants.
Remember, pure, fatty soaps are perfect. You only need a little for a gallon-sized spray, so if you end up investing in a big bottle of Dr. Bronner’s, save the rest for other uses.
Many castile soaps are difficult to find without added essential oils. If you can, chose an unscented option; but if not, try peppermint- or lavender-scented soaps. These essential oils repel insects, so they may help deter the insects that aren’t on the plants when they’re sprayed.
About 98% of your insecticidal spray is just plain water. Since you’re be spraying this water directly onto the plants’ leaves, use clean, fresh water.
Ideally, skip chlorinated tap water and very hard water. I prefer rainwater, water from a spring, or well water. Some gardeners like to use distilled water for spraying, to be certain all impurities have been removed.
Almost any spray bottle will do. Quart-sized sprayers are large enough to handle a few plants at a time, without the stress of carrying a gallon of water around your garden.
Attach a spray cap to a mason jar for a easy, effective, and attractive spray bottle that can fit easy in your garden basket.
Small amounts of neem oil are a great addition to your insecticidal soap recipe. Neem oil disrupts aphids’ life cycle, as well as those of many other destructive insects. It also has a strong scent that insects hate.
Adding in about .5-1% neem oil will make your recipe double effective. While the soap coats the insects’ bodies on your infested plants, neem oil repels them with its scent.
Insects that ingest plants with neem oil fall into a lethargy. They forget to eat, give up on mating, and eventually die. But don’t worry—research shows that neem doesn’t have this devastating effect on bees, butterflies, or birds.
Buy pure, cold-pressed neem oil for best results.
Hot, spicy additions to your soap solution will help drive pests away by making the plant unappealing. Garlic and cayenne powder are two of the most popular additions to insecticidal soap. These easy, accessible additions to the brew will continue to drive insects away from your plants even after the soap has dried.
A dose of vinegar is ideal for plants that are struggling to fight off both an aphid invasion and a mildew problem. Apple cider vinegar is the perfect freshness boost for wet summers and winter house-plants.
To extend your soap spray’s functional life, add a bit of cooking oil to the mix. Cooking oil will cause the solution to dry more slowly.
Remember that these optional additions should be used one at a time. Don’t try to overload your soap spray with bonus products or your plants will suffer. Treat issues individually.
If you add neem oil to your solution, save vinegar for a different application. Likewise, if you’re adding a mildew treatment to your spray, skip the garlic. Oil and vinegar should never be mixed, as they’ll cause emulsifying issues within your solution.
Mixing the Potion
Ok, you’ve got your soap, water, and sprayer. Maybe you even have a little bottle of neem oil ready to go. What now?
First, decide how much you need. If you’re adding in neem oil, mix up small batches. After 8 hours mingling with soap and water, the properties of the oil start to break down.
If you have a large garden or a huge infestation of mealybugs, mix up a gallon. If you’re spritzing a balcony garden, try a quart first.
For a gallon of spray solution mix:
1 gallon water
5 tablespoons soap
1 teaspoon optional efficiency booster (neem, garlic, cayenne, or vinegar)
For a quart of spray solutions mix:
1 quart water
¾-1 tablespoon soap
¼ teaspoon optional efficiency booster
Shake the solution very well. If the resulting solution seems too strong, add a cup (for each gallon), or ¼ cup (for each quart) water to reduce the concentration.
That’s it. Now pour it into your sprayer, and let’s go save some plants.
Using Homemade Insecticidal Soap
Like hair dye, it’s always best to do a patch test on a less visible area of your plant before spraying the whole thing.
Spritz a few underside leaf sections and keep an eye out for signs that your solution is too strong. Wilting and yellowing are common signs that your solution needs to be diluted.
Remember, however, that a weaker solution will be easier on the aphids as well as the leaves.
Shake the spray bottle well before applying. You’ll get the best results from a very well combined solution, so don’t hold back. You can’t over shake this mixture.
Coat healthy, established leaves well and leave the little, tender leaves and flowers alone.
Turn over leaves and spray the underside of plants were greedy aphids love to hide. Douse those insects. The spray works best when applied directly to the body of a bug, so take the time to hunt down all the sneaky pest and spray them down.
Reapply often. Insecticidal soap works while it’s wet. Once the solution dries, it’s not going to catch anymore bugs. Try spraying two or three times in the first month if the infestation is a bad one. Fewer bugs will require less follow up.
Rain will wash away all your efforts, so don’t apply Insecticidal soap right before a storm or while it’s raining.
In contrast, the hot afternoon sun is also a potential problem. Remember that this spray is only effective while wet. If you spray your plants under the noonday sun, the solution will dry quickly and many of your garden pests will escape unharmed.
The best times to spray are early morning and early evening, when the spray will have the longest time to act. Humid, cloudy days are also fantastic for treating your garden.
What About the Bees?
Homemade insecticidal soap is bee, butterfly, and beneficial insect safe. Friendly bugs like bees, ladybugs, and butterflies have a thicker, stronger outer skin that fatty soaps can’t dissolve. So they stay safe.
Insecticidal soap works well against the soft-bodied invaders. Mealybugs, aphids, spider-mites, and thrips beware!
Choosing the right soap will also allow you to tailor the overall impact of your solution. All natural, organic, and biodegradable soaps are key to keeping this treatment environmentally friendly.