How to Use Garlic in Your Garden to Repel Pests Naturally

Walk into just about any kitchen, and you're likely to find garlic. This cooking staple adds depth and intense flavor to meals, making it a common ingredient in many recipes. But did you know that garlic is also useful in the garden? Its pungent aroma and sulfur compounds can deter common garden pests, such as sap-sucking aphids and fungus gnats. But proper application is essential when using garlic as a natural pesticide. Ahead, a pest control expert explains how to use garlic to deter pests, as well as its limitations and mistakes to avoid.

Why Garlic Works As a Pest-Deterrent

Garlic contains bioactive compounds that help deter pests from the garden, says Timothy Wong, technical director of MMPC. The primary one is allicin, a bioactive sulfur compound that gives garlic its strong odor.

"At high concentrations, allicin is lethal to many insects and acts as a contact poison with similar toxicity as synthetic pesticides," says Wong. "However, most DIY formulations don’t reach that level. But at lower concentrations, the strong sulfur smell still acts as a deterrent."

That said, allicin is only present when garlic is crushed or chopped, as this releases an enzyme that converts the amino acid alliin to allicin. Therefore, this method won't work when planting garlic or placing whole cloves in the garden.

The Pests Garlic Helps Control—and Those It Won’t

Garlic won't work for every pest concern. "Soft-bodied insects like aphids and mites are most affected because the oils easily penetrate their thin skin," says Wong. "It is also effective against winged pests like flies, mosquitoes, and fungus gnats because it encourages them to fly elsewhere to lay their eggs."

However, garlic is less effective against hard-bodied pests. "Insects like stink bugs and beetles are less affected due to their hard exoskeletons," says Wong. "They don’t love the smell, but it won’t kill them or force them to abandon a plant." He notes that wasps are also less affected because they lack specific taste receptors for garlic.

How to Use Garlic to Deter Pests

The best way to use garlic to deter pests is to purchase a natural commercial spray containing garlic, as these deliver a much more concentrated dose. "Commercial products have stabilizers and oils mixed in to make the active ingredients last longer," says Wong. Alternatively, can make a DIY spray to help repel pests, as long as it is reapplied regularly.

To make a DIY garlic spray, start by determining how much to mix depending on the size of the garden. "Generally speaking, 1 gallon is a good amount to cover 250 to 500 square feet of garden space," says Wong. Next, blend or crush one head of garlic, then add it to 4 cups of water and 2 tablespoons of vegetable oil. Let it steep for 12 to 24 hours, then strain and add the mixture to a 1-gallon container. Fill the container the rest of the way with water. "Add 1 teaspoon of dish soap to help the solution stick to plants," Wong says.

Spray the mixture onto the stems and undersides of plant leaves affected by soft-bodied insects. Reapply the garlic spray every two to three days. "Rain and waterings will cause it to lose effectiveness much faster," Wong adds.

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Drawbacks of Using Garlic to Deter Pests

Like most pesticides, garlic sprays don't discriminate between pests and beneficial insects. For this reason, Wong says it's important to take a targeted approach during application. "To avoid pollinators, don’t spray flowers directly," says Wong. "Instead, target the main stems and the undersides of the leaves where pests hide. If you’re trying to ward off mosquitoes, spray at dusk to avoid harming daytime pollinators."

Another downside of using garlic sprays, especially homemade ones, is that they are very volatile and will only maintain their efficacy for a couple of days. Frequent reapplication is essential for it to make a notable difference.

Mistakes to Avoid

Using garlic as a pest deterrent is relatively straightforward, but there are a few mistakes to avoid to ensure the method is effective.

• Improper preparation: When making a homemade spray, Wong says the biggest mistake is boiling the garlic or using garlic powder. In both cases, the resulting solution will lack the main bioactive compound, allicin.
• Applying at the wrong time: Never apply these sprays in hot, direct daylight. "This can cause leaf burn (phytotoxicity), and the rapid evaporation also lowers its effectiveness," says Wong. "It is also more likely to cause accidental harm to daytime pollinators like bees."