Can essential oils control slugs? Ask Extension

Gardening season is underway, and you may have questions. To ask one, simply go to the OSU Extension website, type it in and include the county where you live. A photo is very helpful.

Q: I’ve heard essentials oils may be useful in keeping slugs away from my plants and vegetables. Is this true?

A: In our research at Oregon State University, we have studied the role of essential oils in managing slugs for commercial ryegrass and fescue production. We’re developing recommendations for the public, translating this science for a home gardener setting.

It’s exciting for gardeners to have a new, natural and effective method in our toolbox for dealing with slugs and we hope to have these recommendations later this year. In the meantime, here is what the research has found, that you might find interesting too.

The interest in essential oils is widespread and has seen them proven effective against various pests including insects, mites, fungi and nematodes. The results of the study suggest that thyme and spearmint oil could be effective botanical pesticides for controlling common grey garden slug (Deroceras reticulatum) in ryegrass and tall fescue. Thyme and spearmint oil were not phytotoxic to ryegrass and tall fescue (meaning they did not harm the plants).

For the home gardener, essential oils could be used as a barrier. For example, I have done some quick trials by mixing pure essential oil with petroleum jelly and then smearing that in a band around pots in which vulnerable plants are growing. Orchids, for example. Slugs and snails will not cross the barrier. Spraying essential oils in any concentration more than 1% is of concern as it could damage plants.

There are other methods for slug control too that you can see in the information below as well as a recording where I helped answer some similar questions from gardeners during our 2024 Slug Chat with OSU Extension.

— Rory Mc Donnell, Assistant Professor