I use Dr Bronners peppermint soap(vegatarian based soap). Be very carefull if you try this stuff. Very powerful.

What you need to make an insecticidal soap spray is a 1 percent soap in water solution, not much soap. A mix of 1 teaspoon of soap in 1 quart of water is sufficient since more will cause plant stress.

According to the Dr. Bronner website,"liquid soaps use potassium hydroxide to saponify the vegetable oils, versus sodium hydroxide used to make the hard bar soaps." I've also read that peppermint scent repels slugs. So buying a big jug of Dr. B's sounds worthwhile, since I don't have time to track down potassium hydroxide.

Here is a link that might be useful: dr. bronner faq

Any simple soap, such as a mild dish washing soap, can be used to kill insects. Dr. Bronners is a simple soap. Antibacterial soap should not be used. Beware that in spraying soap solution, one is also killing beneficial insects such as preying mantis, ladybugs and green lacewings. Some types of wasps are beneficial because they eat insects. I don't spray, I use a bucket of soapy water to target the plant which is infested.

Lorna

Just be sure you have a soap and not a detergent. Whether the insecticidal soap spray will kill beneficials or not depends on whether or not you spray them. Insecticidal soaps are contact poisons and once dry have no residual affect, however many people that have used detergents as the base of their insecticidal spray have found the detergents will cause leaves to die.

This reminds me that wherever possible we don't spray with soap, but carry around a small bucket of soapy water and drop the pests into that. For instance, snapping off the tops of broad beans infested by aphids, knocking bean weevils off the plants, shaking the earwigs collected overnight in overturned strawberry boxes - all into the bucket. Then dump the soapy water on the ground outside the garden.

The good thing about Dr. Bronner's is that it is soap, and the ingredients are listed on the bottle. It can be really time-consuming to find out the ingredients in commercial dishwashing liquids.