To make your own insecticidal soap, grate 1 bar of soap into a saucepan, and add 1 quart of lukewarm water. Slowly bring the water to a simmer while constantly stirring until all the soap dissolves. Pour the resulting concentrate into a gallon jug, and then fill it with water. Mix 4 tablespoons of the soap concentrate with 1 gallon of water, and allow the insecticidal soap to cool.
Alternatively, to make 1 to 2 percent insecticidal soap, add 5 tablespoons of pure soap in a gallon of lukewarm water, and stir. Add 2 tablespoons of olive oil to thicken the mixture, and stir it until soapsuds form.
Test whether the insecticidal soap is effective by spraying it on a few leaves. Wait a few days, and then observe the leaves for any damage, such as wilting. Dilute the solution further if you observe any damage.
Only use bar soap or pure liquid soap to make insecticidal soap. Other ingredients that are safe to use include corn and safflower oil. According to SFGate, olive, corn and safflower oil thicken the insecticidal soap, helping it to stick to leafage.
Avoid using detergents, as they contain additives that harm plants. Also avoid using hard water as the solvent. This water contains minerals that cause soap scum deposits on leaves. For the best results, spray all stems and the tops and bottoms of leaves with the solution.