Instead of relying on different remedies or control methods, what if one plant could help protect another from pests, especially gnats that develop in the soil and become harmful to plants over time?
In nature, many plants can repel gnats on their own, but for others, gardeners use home remedies such as neem oil, baking soda, cinnamon, or vinegar.
Garlic also comes into focus, but does garlic really kill fungus gnats or simply keep them away? The short answer is yes, garlic can help kill fungus gnats, but it does not kill them entirely.
However, its effectiveness improves with yellow sticky traps that target flying adult gnats. It’s also important to clarify that garlic plants themselves don’t actively control fungus gnats.
Here, I am talking about the garlic cloves, which need to be prepared as a remedy and applied properly to target fungus gnats in the soil.
Does Garlic Really Kill Gnats in Plants? Larvae vs. Adults
Garlic is often used as a natural pest remedy because it contains allicin, a sulfur compound known to repel insects and affect some pests.
According to This Old House, allicin is released when garlic is crushed, and its strong smell helps drive away many common garden pests.
Gardening sources such as Plantura suggest that allicin may harm fungus gnat larvae in the soil, which is why many indoor gardeners use garlic cloves or sprays and notice fewer gnats over time.
However, garlic is not scientifically proven as a complete or guaranteed solution, and agricultural experts do not list it as a primary control method.
Overall, garlic may help, especially against larvae, but it works best as a supporting treatment rather than a stand-alone fix.
Larvae
Several gardening sources say garlic works better against these larvae than against adult gnats. Because garlic contains allicin, it can kill fungus gnat larvae in the soil.
The MOOWY gardening blog also states that when garlic cloves are chopped and mixed into moist soil, they can quickly kill the larvae.
These observations suggest that substances released from crushed garlic can move through damp soil and affect the larvae feeding near plant roots.
We can say “garlic is best viewed as a natural, homemade option rather than a tested, guaranteed solution.”
Adults
Adult fungus gnats are small, weak flying insects, and garlic does not usually kill them directly. Instead, garlic works mainly as a repellent.
When garlic is crushed, it releases a strong smell that can confuse or drive away flying gnats, causing them to avoid treated plants.
Some indoor gardening guides recommend placing crushed garlic on the soil because its odor helps keep fungus gnats away.
Trusted home-gardening sources also explain that garlic sprays, often mixed with mild soap, make plants less attractive to pests.
However, garlic should not be expected to kill adult gnats on contact during normal home use. Its real value is in discouraging them from landing or laying eggs.
Even scientifically proven treatments like BTI do not work on adult gnats, which is why adults are usually controlled with sticky traps or by reducing soil moisture rather than relying solely on sprays.
How to Use Garlic to Kill Gnats in Plants? Step-by-Step
According to Gardening Know How and This Old House, here are steps for using garlic to repel gnats around plants or in the yard.
Step 1: Using fresh garlic in the soil
- Take 3 to 6 fresh garlic cloves, peel them, and lightly crush them to release their natural compounds.
- Place the crushed cloves on the top layer of the potting soil or gently mix them into the soil surface.
- Replace the garlic once it dries out, usually after about a week. Lightly covering the cloves with soil can help reduce mold and keep them effective longer.
Step 2: Making a garlic water solution
- To prepare a garlic spray or soil drench, crush about 6 garlic cloves and add them to roughly 2 liters of water.
- Gently heat the mixture for around 15 minutes, then allow it to cool.
- Home-gardening experts recommend straining the liquid to remove garlic pieces before use.
- Dilute the strained liquid with water at about one part garlic solution to ten parts water to avoid harming plants.
Step 3: Applying the garlic solution
- Pour the diluted garlic water evenly over the soil and lightly spray the plant leaves, especially underneath, where gnat larvae may rest.
- Adding a small drop of mild liquid soap helps the mixture stick to the leaves.
- Apply this treatment once a week to maintain its effect and discourage gnats.
Step 4: Using garlic powder (optional)
- If fresh garlic is unavailable, lightly sprinkle a few teaspoons of garlic powder onto the soil surface and water as usual.
- Moisture helps release garlic compounds slowly into the soil.
- This method is less commonly documented but works on the same principle as fresh cloves.
Step 5: Use with care
- Avoid using strong or undiluted garlic liquids on plants, as they may cause leaf damage.
- Always observe how your plant reacts after the first application and adjust the strength if needed.
Limitations and Cautions
- Garlic is not guaranteed to kill all gnats. It usually reduces gnat numbers rather than eliminating them completely, so also combine other methods, especially sticky traps.
- Strong or undiluted garlic can harm plants, causing leaf burn or stunted growth. Always dilute garlic mixtures and test on one plant first, especially on seedlings or sensitive plants.
- It can repel or harm helpful insects, pollinators, and soil organisms. Use it only on affected plants and sparingly to avoid disturbing your garden’s balance.
- Heavy or repeated garlic use can alter soil chemistry, slightly acidifying the soil and affecting microbes. Occasional clove applications are safe, but avoid burying too many cloves too often.
- Garlic is less effective than specialized treatments such as BTI, neem oil, or sand barriers. Its effect is mostly anecdotal, so it works best as a supporting, natural solution rather than the main control method.
- It can be toxic to pets if ingested, and its strong smell can linger on hands and furniture. Keep pets away from treated areas and use in a well-ventilated space.
How Long Does Garlic Take to Kill Gnats?
Fungus gnats go through their life cycle in about 2 to 3 weeks indoors. Eggs hatch in a few days, larvae feed in the soil for around 10 days, and then they become pupae for a few more days.
Garlic mainly works by killing larvae or keeping adults away, so you need to keep using it for at least one full life cycle.
Gardeners say that garlic can start affecting larvae within a few days, but to really see results, most people apply it every week for 2 to 4 weeks.
This covers any newly hatched larvae. Many notice that the number of gnats starts to drop after 2 to 3 weeks of consistent use.
Remember, garlic isn’t a quick fix. If adult gnats are still around after a month, it’s a good idea to combine garlic with yellow sticky traps and other specialized soil drenching remedies, such as hydrogen peroxide, BTI, or nematodes.
Remember, do not use multiple soil-based remedies together, especially BTI with hydrogen peroxide or nematodes.
