How to Use Chop, grind, or liquefy one garlic bulb and one small onion. Add 1 teaspoon of powdered cayenne pepper and mix with 1 quart of water. Steep 1 hour, strain through cheesecloth, then add 1 tablespoon of liquid dish soap to the strained liquid; mix well. Spray your plants thoroughly, including leaf undersides. Store in refrigerator up to a week. Avoid eye or mouth contact.