Soap is one effective and inexpensive means of controlling common pests on plants, indoors and outdoors. Unlike many chemical pesticides, these you can use without worrying you are exposing yourself, or the environment, to toxic chemicals. Dish soap sprays are safe for most plants; however oldfashionedliving.com does warn it is unsafe for cauliflower, squash and red cabbage.
Pour 1 cup of sunflower oil or safflower oil in a spray bottle, as suggested by oldfashionedliving.com. The oil helps the soap spray stick to the plant's foliage. Add 1 cup of water and 2 tbsp. of a mild liquid dish soap.
Put the cap on the spray bottle and shake it well to mix the oil and soap. In the early morning or evening ( to prevent sun scald) spray garden plants with the formula. You can also use soap spray on houseplants--in that case you won't need to worry about the time of day. As long as the plant is away from direct sunlight, spraying is fine.
Spray the tops of the leaves, as well as the undersides where some insects like to hide. Also spray the stems, if necessary (look for insects themselves, or signs of insects such as webbing).
Oisat.org warns you should test the solution on one plant, first, before spraying several. This way you can make sure you won't harm the plants with the mixture.
Repeat the application every two weeks, or more frequently--depending on the insect infestation.