Why People Put Soap Near Tomato Plants — And Whether You Should Too

We may receive a commission on purchases made from links.

Here at Tasting Table, we're all about a DIY remedy. But, admittedly, some are more sound than others. Today, we're shining the spotlight on one affordable, non-toxic product for keeping ants, rabbits, and deer away from your tomato plants (allegedly). To keep harmful chemicals away from food, and plant-damaging pests out of the garden, many gardeners place a few bars of soap around their tomato plants. Specifically, Irish Spring deodorant bar soap.

Per the theory, the secret ingredient is picaridin — a manmade compound found in Irish Spring bar soap that (happily) also repels insects. Meanwhile, the soap's strong citrus fragrance is thought to help keep rabbits and deer away, and many gardeners maintain that Irish Spring's lemon and eucalyptus oil repel mosquitos. Although, in actuality, the ingredients label listed on Irish Spring's packaging currently does not list either oil. Don't ditch your citronella candles just yet. 

To use the bar soap strategy, simply cut that soap into chunks and place them near your tomato plants. For taller plants, place the soap chunks in mesh bags and hang the bags on stakes a foot or two off the ground. Alternatively, the soap can also be shredded with a cheese grater, then sprinkled around the garden for more thorough distribution. Irish Spring bar soap won't harm vegetation, grass, or soil, but water and exposure will break down the soap's active ingredients over time. Replace the bars (or throw out a fresh sprinkle of soap shreds) once a month, or after a rainstorm.

This natural pest control method may be gentle and non-harmful to soil health, but it's worth noting that the efficacy of these claims are often overblown. The bar soap does contain strong fragrances, which can impart a slight benefit when it comes to deterring insects, but there's no strong scientific evidence that it's effective for animals. According to Colorado State University, the only sure way to prevent deer damage in your garden is to build a tall fence or other physical barrier. The University also notes that "[d]eer have been reported to eat the soap bars." There doesn't seem to be any connection between Irish Spring and repelling tomato worms, either. 

Nonetheless, many gardeners turn to Irish Spring to keep their tomato plants safe, and a DIY method this widely-known can't be entirely wrong. The University of Missouri maintains that the bar soap method can, in fact, help reduce deer damage even just by the visual cue of a foreign bar of soap hung near a tomato plant. "Each bar appears to protect a radius of about 1 yard," says the University, although, "When food is scarce, deer may ignore both taste and odor repellents." If ants, rabbits, or deer pose a recurring problem for your tomato plants, this method might be worth a shot — and, if not, it won't set you back much. A two-pack of Irish Spring bar soap currently runs for just $8.49 on Amazon.