As I understand it, Insecticidal Soap is an organic method of garden pest control that involves spraying a blend of soap, fats and water directly onto insects that quickly kills them without harming your plants. You have to hit the buggers directly, but I’ve found the commercial stuff very useful for those insects who sit on your plants munching and giving you the finger even as you walk right up to them.
The bottle I bought was not pricey, but far more expensive than the homemade version would be, plus I could put it in my big sprayer and go to town rather than slowly spritzing and wearing out my fingers. However, internet searches seem to be equal parts of “it’s easy to make, here’s granny’s recipe” and “it’s deceptively easy to get it wrong and then you’ll scorch your plants, always buy it premade.”
I have canola oil. I have Dr. Bronner’s tea tree oil scented glycerine liquid soap, and I have dishwashing detergent. Also, I have stores available nearby. Can I make my own mix safely and cheaply? Can I make a concentrate to mix with water when needed or does it need to be from scratch each time?
Experiment away, but pick weeds/non-essential plants to test your concoctions on.
Also, check the insecticidal soap labels for species that seem especially susceptible to leaf damage from the spray, and do your spraying at cooler times of the day and not in bright sunlight.
Homemade plant sprays can work out well, but I also remember the time I decided to make my own spray from hot peppers and ground them up in a kitchen food processor. The resulting toxic gas practically drove Mrs. J. and I out of the house.
I have even heard of people using dish washing liquid. By the way DE works well with controlling insects. However diatomaceous earth won’t work if it gets wet, so it’s use outside is limited
I had some aphids on some new growth. I mixed up a batch of soap (about 3 tbs of Dawn dishwashing liquid in a spray bottle full of water) and gave them a good spritz. The buggers were gone the next day.