As I’ve mentioned before, when you make home made soap for a living, you’re bound to have a whole lot of it lying around. With a three-person household it’s unlikely that we’re going to be using all the scraps bathing (unless we were all to take a few more showers a day), so I’m always on the lookout for other neat ways to use my handmade soap.
This use is very neat, and it’s very useful for spring, too. You can use soap in combination with other common ingredients to create insecticidal soap – a human and environmentally friendly concoction that kills many bugs that harm your plants. The soap mixture will kill soft bodied insects like spider mites and aphids, but is relatively benign to harder bodied insects like bees, as well as mammals. It can potentially kill predatory mites, which feed on spider mites, but if you’ve got an infestation of spider mites, you have to wonder if there are predatory mites in sufficient quantity to do the job unaided.
Insecticidal soap doesn’t leave a long-lasting protective barrier on the plant, but it will quickly kill susceptible insects it comes into contact with. You can certainly buy a premixed variety, but making it yourself is a project that’s fun, easy and rewarding. I say rewarding because I find being resourceful to be very rewarding. It’s also nice to know exactly what’s going into the pesticides you use around your home. Even if you’re not a die-hard environmentalist, you can appreciate using an effective pesticide that’s biodegradable, especially if you have young children.
There are a lot of variations on this recipe out there. I’ll probably experiment with some of the more exotic ingredients in a later posting, but I was looking for a basic, easy recipe to use as a starting point.
Here’s what you need:
Insecticidal Soap Recipe
1 Tbsp grated soap
1 tsp vegetable oil
1 quart of warm water
It’s best that the soap actually be soap - a detergent like you might find in “soap-like” products like body bars, beauty bars, or deodorant bars may or may not work. Most sources I found state that they will not. I suggest a no-frills soap, like my non-colored, non-scented Plain Jane soap. It’s easy to measure if you shave or grate some off the bar. It’s even easier if you pulverize it in a food processor after grating it. Add the soap to the water and let is dissolve. Add the vegetable oil, put the mixture in a plant or garden sprayer, shake well, and spray where needed. The vegetable oil supposedly allows the soap to stay on the plant a bit longer for some added protection.
It’s best to test the soap mixture on a small, inconspicuous part of the plant before treating the whole thing. Treat the plant and wait for a couple days, and be on the lookout for yellow or brown spots or leaf edges. If my math is correct, the recipe above should give you a solution that is a bit weaker than the 2% common in pre-prepared varieties. You might be able to go a bit stronger, but if you detect problems with any concentration, you can try cutting down the soap concentration to make a weaker solution. Avoid using the mixture on new growth or plants that are under stress. Some plants, like ferns or some tomatoes will not tolerate the soap well.
Spray the plants (especially the underside of leaves, where insects like to hang out) in temperatures lower than 90 degrees, and when they are not in full sun. Early in the morning when it is cool is often a good time to treat, as this will allow the mixture to work longer before it dries. This will also ensure that the mixture will dry; a night-time or dusk application could encourage mold growth. Leave the soap on for a couple hours, and then wash it off to reduce the likelihood of damage. You may need to do a second treatment in a week, and perhaps a third the week after.
As with any mixture designed to kill or clean anything, be careful. Eye protection and gloves are always a good idea when using a pesticide. The soap is unlikely to hurt you, but it can potentially irritate your eyes, and possibly your skin.