What Effect Does Vegetable Oil Have On Plants?

With the increase of interest in organic gardening in recent decades, homemade pest control has become more popular, including recipes with vegetable oil as a main ingredient. The lack of toxins and chemicals make such homemade sprays attractive. Although vegetable oil does not leave harmful chemicals behind that can affect plant growth and health, it can affect plants negatively if it is not applied at the proper time.

Olive oil and tomatoes.
credit: Inácio Pires/Hemera/Getty Images
Vegetable oil can help with pest control.

Increase in Oil Usage

Homemade pest control mixtures increasingly contain vegetable oil, or have vegetable oil listed as an alternative ingredient to mineral oils, which are derived from petroleum.

Function

Vegetable oil, when sprayed on plants, helps to kill insects. The oil coats the bodies of the insects as they come into contact with the oil, breaking down their outer shells. The vegetable oil will then wash away in rain or wear away in the sun, leaving no harmful chemicals on the plants.

Types

Vegetable oils can be made from numerous kinds of vegetables. Cottonseed oil and soybean oil are the two most effective varieties when used as insecticides.

Effects

Most garden plants are not extremely sensitive to oil, but many can still become burned if the oil is not applied correctly. Applying vegetable oil to plants in extremely hot or sunny weather will result in burned leaves.

Considerations

When using vegetable oil recipes as a pesticide, avoid spraying the oil on the plants when it is highly humid or directly before watering the plants, which can reduce its effectiveness.