As of late September 2026, the nights here in Riverside are starting to cool, and for years this was the week I restocked. Cotton balls soaked in peppermint oil under the kitchen sink, a dryer sheet folded into the garage cabinet, another behind the water heater. I refreshed them whenever the smell faded. I hadn’t seen a mouse in my kitchen here in California, which felt like proof it was working.
Riverside County’s vector control guide for residents has a better test than my nose. As a rule of thumb, it says, if you can see light around the door, rodents can enter. The same guide says gaps around pipes and electrical conduit should be sealed and cracks around windows weatherproofed. It’s all about the openings. By that test, a garage door with daylight along the bottom is an open door.
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What the extension expert says
The question has been put to extension experts directly, on Ask Extension, and the expert response was flat: “Peppermint is not going to deter mice from entering your home.” The same answer lists what does: snap-trap, cut off whatever food source they’re using, and, the most important part, find their entrances and block them with unchewable material such as steel wool, hardware cloth or concrete patching.
Why the gap matters more than the smell
The University of California’s pest management program explains the timing and the size of the problem. Where outdoor populations of house mice exist, it says, they frequently enter homes in autumn when nighttime temperatures become colder. And house mice can squeeze under gaps ¼ inch tall and through openings 3/8 inch wide. A cotton ball in the cabinet doesn’t close a gap that size…