Dealing with Fungus Gnats Without Losing Your Mind

You’re sitting on the couch, relaxing after a long day, and a tiny black fly buzzes past your face. Then another. And another.

You look over at your plants and there’s a small cloud of them hovering around the pots.

Fungus gnats. The fruit flies of the plant world. They don’t bite, they don’t damage plants much, but they’re incredibly annoying and they multiply fast.

The good news is that fungus gnats are easy to get rid of once you understand what they want. The bad news is that if you don’t change your habits, they’ll keep coming back.

What Are Fungus Gnats?

Fungus gnats are tiny flies (about 1/8 inch long) that look like miniature mosquitoes. The adults fly around your plants looking for damp soil to lay eggs in. The larvae live in the soil and feed on organic matter, fungi, and sometimes plant roots.

Life cycle:

Adult gnats lay eggs in moist soil
Eggs hatch in 4-6 days
Larvae feed in the soil for 2 weeks
Larvae pupate and emerge as adults
Adults live for about a week, laying more eggs

One generation takes about 3-4 weeks. If you don’t break the cycle, you’ll have gnats forever.

Why You Have Fungus Gnats

Fungus gnats thrive in one condition: consistently wet soil.

Common causes:

Overwatering your plants
Soil that doesn’t drain well
Pots without drainage holes
Organic matter decomposing in the soil (like compost or peat moss)
High humidity combined with wet soil

If your soil stays damp for days after watering, you’ve created a fungus gnat resort.

Step 1: Let the Soil Dry Out

This is the most important step. Fungus gnat larvae can’t survive in dry soil.

How to do it:

Let the top 2-3 inches of soil dry out completely before watering again
For plants that prefer moist soil, let at least the top inch dry
Check the soil with your finger before watering
Water less frequently in winter when plants aren’t actively growing

Why it works: The larvae live in the top few inches of soil. If that layer dries out, they die. Adults can’t lay eggs in dry soil either.

Warning: Don’t let the soil get so dry that your plants wilt and die. You’re aiming for the top layer to dry, not the entire root ball.

Step 2: Use Yellow Sticky Traps

Yellow sticky traps catch adult gnats. They don’t solve the root problem (wet soil), but they reduce the adult population so fewer eggs get laid.

How to use them:

Stick the traps in the soil near the base of your plants
Replace them when they’re covered in gnats (usually every 1-2 weeks)
You can also hang them near windows where gnats congregate

Where to buy: Hardware stores, garden centers, or online. They’re cheap and effective.

Pro tip: Fungus gnats are attracted to the color yellow. If you have a lot of gnats, put traps in every pot.

Step 3: Apply a Soil Drench

If drying out the soil and using sticky traps aren’t enough, you can kill the larvae directly with a soil drench.

Option 1: Hydrogen peroxide solution

Mix 1 part 3% hydrogen peroxide with 4 parts water
Water your plants with the solution until it runs out the drainage holes
The peroxide kills larvae on contact and breaks down into water and oxygen
Repeat every 5-7 days for 2-3 weeks to catch multiple generations

Option 2: Mosquito Bits (BTI)

BTI (Bacillus thuringiensis israelensis) is a bacteria that kills fungus gnat larvae but is harmless to plants, pets, and people
Sprinkle Mosquito Bits on top of the soil or soak them in water and use the water to water your plants
Reapply every 2-3 weeks until gnats are gone

Option 3: Neem oil soil drench

Mix neem oil with water according to package instructions
Water the soil thoroughly
Neem disrupts the gnats’ life cycle
Repeat every week for 3 weeks

Which method is best? I prefer hydrogen peroxide because it’s fast, cheap, and safe. BTI is a close second if you have a really bad infestation.

Step 4: Add a Top Dressing

Covering the soil surface makes it harder for adult gnats to lay eggs and harder for larvae to emerge.

Options:

Sand: A 1/2-inch layer of sand on top of the soil dries quickly and creates a barrier
Pebbles or gravel: Decorative and functional - gnats can’t penetrate it
Diatomaceous earth: Sharp particles that kill larvae and adults on contact (use food-grade DE)

Pro tip: Sand is my favorite. It’s cheap, looks clean, and dries out fast. Just make sure to use coarse sand, not fine sand that clumps.

Step 5: Improve Drainage

If your soil is staying wet for more than a few days, it’s time to repot with better-draining soil.

How to make soil drain better:

Add perlite, pumice, or coarse sand to your potting mix (20-30% by volume)
Use pots with drainage holes (non-negotiable)
Avoid soil mixes with a lot of peat moss or coco coir (they hold too much water)
Make sure your pot isn’t sitting in a saucer full of water

When to repot: Spring is ideal, but if you have a bad gnat problem, repot anytime.

Step 6: Break the Cycle

Even if you kill all the gnats you can see, there are probably eggs and larvae in the soil. You need to keep up your efforts for at least 4-6 weeks to break the entire life cycle.

The plan:

Week 1-2: Let soil dry out, apply sticky traps, do a hydrogen peroxide drench
Week 3-4: Continue drying out soil, replace sticky traps, do another drench if needed
Week 5-6: Monitor for new gnats. If you see any, repeat the process

How you know you’ve won: No new gnats for 2 weeks straight. Keep checking because sometimes a few stragglers hang on.

What Doesn’t Work

Spraying the adults with insecticide. You might kill a few, but the larvae in the soil will just keep hatching. You’re treating the symptom, not the cause.

Watering with cinnamon. Some people swear by this, but it’s not reliably effective. Cinnamon has antifungal properties, but it doesn’t kill larvae.

Ignoring the problem. Fungus gnats don’t go away on their own. They multiply exponentially if you don’t do something.

Only using sticky traps. Traps catch adults, but they don’t stop the larvae in the soil from hatching into more adults.

Preventing Fungus Gnats

Once you’ve gotten rid of them, here’s how to keep them from coming back:

Water correctly: Let the top layer of soil dry out between waterings. This is the single most important thing you can do.

Use well-draining soil: Add perlite or sand to your potting mix.

Empty saucers: Don’t let pots sit in standing water.

Quarantine new plants: Keep new plants away from your collection for a few weeks to make sure they’re not bringing pests with them.

Use bottom watering occasionally: If you bottom water (set the pot in a tray of water and let it soak up moisture from the bottom), the top layer of soil stays dry. Gnats hate that.

Why I Don’t Panic About Fungus Gnats Anymore

The first time I got fungus gnats, I thought my entire plant collection was doomed. I tried everything at once - sprays, traps, repotting, prayers. It was chaos.

Now I know better. Fungus gnats are a symptom of overwatering. Fix the watering, let the soil dry out, use sticky traps, and they’re gone within a few weeks.

My kids think the yellow sticky traps are hilarious. They check them every day to see how many gnats we’ve caught. It’s turned pest control into a game.

And I’ve learned to let my soil dry out more than I think I should. Most plants can handle a little drought. Very few plants can handle constantly wet soil.

Fungus gnats taught me that.

The Bottom Line

If you have fungus gnats:

Let the soil dry out between waterings
Use yellow sticky traps to catch adults
Do a hydrogen peroxide or BTI soil drench to kill larvae
Add a layer of sand or pebbles on top of the soil
Repeat for 4-6 weeks to break the life cycle

Fungus gnats are annoying, but they’re not the end of the world. Fix your watering habits and they’ll disappear.

And next time you see a tiny fly hovering near your plants, you’ll know exactly what to do.