Do your plants need a bath? Are you sure? We have had a major invasion of spider mites and squash bugs. I don't like to use anything that could poison us or harm fish and such. Very few insecticides are used here at all. The exception is soap. Soap will smother insects. In order for insecticidal soaps to work, you must get them on the bug. To avoid killing your good bugs, you must keep the soap off those bugs. I make my own soap mixture. It is pink and smells like roses.
Zote soap (laundry isle of grocery story)
Mix 2 to 3 tablespoons of chopped or shredded soap in 3 cups of water and nuke for one minute. Stir the mixture with a whisk and let cool. Poor through a fine strainer into a spray bottle.
Spray the mixture onto infested plants getting it on the bug. Do this in the evening in order to avoid burning your plants. After about five minutes rinse off the plants, again, to avoid burning the leaves. Squash bugs will die in less than a minute. It is fun to watch them fall over dead. As I cannot actually see a spider mite, killing them is not quite as much fun. A couple of days after treating a tomato plant for spider mites, it looks much better, so spider mites are obviously controlled.
Zote soap is really cheap at less than a dollar a bar. It last forever and really helps get stains out of clothes. Trust me, the monkeys can make some stains.