Using Dormant Oils in the Garden

Photo: Gustavo Fring (Pexels)

When it comes to controlling pests in the garden, early prevention is key and one of the first things you can do at the beginning of the year is apply dormant oil.

What is dormant oil? It is a refined horticultural oil usually derived from minerals and plants. Generally, horticultural oils are used during the dormant season but some brands can be used year-round. Check the label for proper usage.

Horticultural oils are non-toxic and basically work by smothering overwintering insects and mites, including eggs and immature scale. Dormant oil does not sterilize plants; it reduces pest populations by coating breathing structures and disrupting egg development. Keep in mind that it is not a selective product, so it will smother any insects, including beneficial ones. It is therefore important to only apply where necessary.

Horticultural oils are widely used for fruit trees, but they can also be used on any plant that is prone to insect damage. Roses can greatly benefit from this application.

For best success, apply dormant oils when the plants are dormant, before budbreak. In western Washington state, January – March is good, depending on the mildness of the winter. This year, we are experiencing a mild winter, so it is recommended to apply now.

When applying to smaller plants, such as roses, coat the stems and the area on the ground surrounding the plant. For evergreen plants, apply the spray both on the outside and undersides of the leaves.

For best results, Yard N’ Garden Land recommends a combination of Monterery Horticultural Oil with Monterey Liqui-Cop as follows:

Mix 1 oz. of Liqui-Cop and 2 oz. Horticultural Oil with 1 gallon of water. Apply three times on or around the following days – New Year’s Day, Valentine’s Day, and early/mid March.