1 gallon water 2 1/2 tablespoons pure-castile liquid soap 1 tablespoon vegetable oil (optional)
Fill a gallon-size spray container with water, then add the soap and oil. Mix or shake the container thoroughly before using.
To scale the recipe for smaller applications, use 2 teaspoons pure-castile liquid soap for every 1 quart water.
Dry conditions and hot weather (above 90°F) can increase plant stress and increase your plants’ sensitivity to soap, so avoid spraying on a hot, sunny day and make sure your plants are well watered first.
If you’re trying to treat houseplants, be sure to protect the surroundings from overspray, or move the plants to an area where you can spray freely, like a patio or garage.