In a small jar, combine neem oil with castile or dish soap.
Add enough warm water to almost fill the jar, put on lid, then shake vigorously until thoroughly mixed.
Pour the mixture into a one-gallon garden sprayer and add enough water to equal one gallon.
OPTIONAL: Add 2 teaspoons of liquid kelp or fish emulsion to the sprayer to feed your plants while you treat them.
Thoroughly drench the your plants' leaves and stems weekly. (Don't forget the undersides of your leaves!)
Notes
Never apply horticultural oils to plants when temperatures outside are above 90°F (32°C), when they are stressed by drought, or if they have been treated with sulfur within the last two weeks.