Whether it is purchased commercially or made at home from simple ingredients, white oil is used as an insecticide for home gardening. It is said to be effective for killing a variety of insect pests, including aphids, citrus leaf miners, caterpillars, mites, scale, and mealy bugs. As a mechanically based pesticide, white oil works by coating and suffocating insects rather than through any kind of chemical action, so insects cannot become resistant to it. Gardeners commonly use the oil on fruit and citrus trees, ornamental plants, and roses, among other types of garden plants.
While commercial preparations of this concoction typically contain petrolatum products, recipes for homemade white oil recommend the use of vegetable oil as the main ingredient. In general, recipes call for a combination of liquid detergent and cooking oil. This mixture is shaken together, then diluted with water and applied to plants with a spray bottle or mister. Gardeners recommend spraying the finished mixture on both sides of infested leaves.
According to some sources, gardeners should avoid using white oil on the soft or hairy leaves of certain plant varieties, which can be harmed by the soap ingredient in the mixture. It is believed that this pesticide is most effective when applied to plants in the late evening or early morning, as temperatures are coolest during these times. Using the mixture during very warm periods could damage some plants by producing a burned effect on the foliage.
A general recipe includes about 2 cups (480 mL) of vegetable oil combined with about a half cup (120 mL) of liquid soap. Cover and shake the mixture, then dilute it with water for immediate use in a mister or spray bottle. This homemade mixture could last up to three months if stored in a dry, cool location in an airtight container. Liquid castile soap and olive oil are said to be ideal ingredients to create white oil for use on plants. For those who do not have liquid soap available, it is possible to use shavings of bar soap as an alternative ingredient.